Defects in Amino Acid Catabolism and the Urea Cycle

Home , Costeff syndrome, Glutaric aciduria type 1, Hyperhomocysteinemia

Chapter 181 Defects in amino acid catabolism and the urea cycle

GEORG F. HOFFMANN* AND STEFAN KO¨ LKER Department of General Pediatrics, University Children’s Hospital Heidelberg, Heidelberg, Germany

INTRODUCTION organizations can offer support. Since treatment is time- and cost-intensive, often lifelong, and mostly Defects in amino acid catabolism and the urea cycle performed at home, regular training and support of result in an accumulation of metabolites upstream of patients and their families is essential. Unfortunately, as the defective enzyme (amino acids (AAs), organic acids for all chronic diseases, average compliance with recom- and/or ammonia) causing intoxication. Phenylketonuria mendations has been found as low as 50%, e.g., in PKU. (PKU) is the most frequent AA disorder (AAD) in Individual defects in AA catabolism and the urea Caucasians. Breakdown of AAs results in the release cycle usually have a low prevalence except for some of ammonia that is detoxified by the urea cycle. Hyper- communities with high consanguinity rates. However, ammonemia is the biochemical hallmark of urea cycle the cumulative prevalence of these disorders is consider- defects (UCDs). able (i.e., at least> 1:2000 newborns; Schulze et al., After an uneventful pregnancy and an initially asymp- 2003). Detailed information on diagnosis, genetic test- tomatic period, the onset of symptoms in these disorders ing, treatment and follow-up is available at the following varies from neonatal metabolic decompensation to late online databases: onset in adulthood. In childhood, metabolic decompensa- OMIM (http://www.ncbi.nlm.nih.gov/omim) tions are triggered by excess intake of protein and, impor- This is the online version of “Mendelian Inheritance in tantly, secondary to breakdown of body protein during Man,” the oldest and most widely used database of catabolic episodes. Treatment includes: (1) reduction of genetic disorders, founded by Victor A. McKusick. toxic metabolites by dietary restriction of precursor The number allocated to entries in the OMIM catalogue AAs, prevention of catabolism, stimulation of residual is used in scientific publications worldwide for the exact enzyme activity and detoxification strategies, and (2) sub- identification of individual genetic disorders. stitution with depleted substrates, vitamins and cofactors, GeneClinics (http://www.geneclinics.org) such as biotin or cobalamin. However, treatment efficacy This expert-written, peer-reviewed medical database is often low if patients are diagnosed after the onset of contains information on diagnosis, treatment and genetic symptoms. As a consequence, in many countries newborn testing of genetic disorders. screening programs have been established for some of Orphanet (http://www.orphanet.infobiogen.fr) these disorders. Neurological disease is common, particu- This database contains peer-reviewed information on a larly in untreated patients, and the manifestations are var- large number of genetic and non-genetic conditions. ied. The most frequent are: (1) mental defect, (2) epilepsy, The information is available in English and French. and (3) movement disorders. Successful treatment of affected individuals is often CLINICAL SPECTRUM AND DIAGNOSTIC challenging and requires careful supervision by metabolic WORK-UP centers involving an experienced interdisciplinary team. Evaluation and treatment of neurological symptoms A careful (family) history may reveal important clues to should be performed by a neuropediatrician and/or later diagnosis. Most disorders are inherited as autosomal on by a neurologist. In addition, parent and patient recessive traits which may be suspected if the parents

*Correspondence to: Professor Dr. Georg F. Hoffmann, University Children’s Hospital Heidelberg, Department of General Pedi- atrics, Im Neuenheimer Feld 430, D-69120 Heidelberg, Germany. Tel: þ49-6221-564002, Fax: þ49-6221-564388, E-mail: Georg. [email protected] 1756 G.F. HOFFMANN AND S. KO¨ LKER are consanguineous or the family has a confined ethnic abnormalities, cortical or cerebellar atrophy, and injury or geographic background. They may be more frequent of the basal ganglia, can be derived from cranial mag- in certain communities (e.g., Amish), ethnic groups (e.g., netic resonance imaging (MRI). Ashkenazi Jews, Arabic tribes) or countries that have seen little immigration over many centuries (e.g., INDIVIDUAL DISORDERS Finland). Urea cycle defects Many disorders already manifest in the first days of life with progressive irritability or drowsiness. Most typ- Hyperammonemia (plasma ammonia: >80 mmol/L in ically, a young infant may vomit or refuse to feed and newborns; >50 mmol/L after the newborn period) is then rapidly deteriorates. The initial erroneous diagnoses caused by decreased detoxification of ammonia (NH3) are usually neonatal sepsis or intracranial hemorrhage. and/or increased production (e.g., by intestinal urease- A presumptive diagnosis of an inborn error of metabo- producing bacteria). Decreased detoxification results lism (IEM) of AA catabolism or urea cycle within 24–48 from inherited or acquired deficiency of key enzymes hours of the onset of symptoms is indispensable for a and transporters of the urea cycle (Fig. 181.1), or bypasses satisfactory outcome. Timely and correct intervention of the liver (e.g., open ductus hepaticus). Secondary during the initial presentation of metabolic imbalance impairment of NH3 detoxification results from condi- and during later episodes is an important prognostic tions where glutamate or acetyl-CoA are decreased, factor. Evaluation of metabolic parameters including such as in OADs, b-oxidation defects, carnitine deple- analyses of blood gases, serum glucose and lactate, tion, or valproate therapy, or where toxic acyl-CoAs plasma ammonia and AAs, acylcarnitine profiling in are increased, such as in propionic, methylmalonic, or dried blood spots, and organic acid analysis in urine isovaleric aciduria. should be performed on an emergency basis in every Hyperammonemia is neurotoxic resulting in brain patient presenting with symptoms of unexplained meta- edema, convulsions, and coma. A particular injury to bolic crisis, intoxication, or encephalopathy (Blau et al., the bilateral lentiform nuclei and the deep sulci of the 2003, 2005). Routine clinical chemistry alone is often insular and perirolandic regions occurring in the new- unrevealing. born has been reported (Takanashi et al., 2003) A substantial number of patients present differently (Fig. 181.2). Neuropathological evaluation reveals an with acute encephalopathy or chronic and fluctuating alteration of astrocyte morphology including cell swell- progressive neurological disease. The so-called cerebral ing (acute hyperammonemia) and Alzheimer type II organic acid disorders (OADs) (e.g., glutaric aciduria astrocytosis (chronic hyperammonemia) with ulegyria type I) present with (progressive) neurological symp- in the most severe cases, which can build up within a toms, such as ataxia, myoclonus, extrapyramidal symp- few weeks (Kornfeld et al., 1985). Mild cerebral and cer- toms, and “metabolic stroke” (Hoffmann et al., 1994). ebellar atrophy and infarct at bilateral posterior putamen Important diagnostic clues, such as white matter and insular cortex localization on conventional MRI

NAGS N-acetylglutamate Glutamate + Ammonia Orotic acid CPS1 Carbamyl- Orotidine − phosphate HCO3 Uracil Citrulline OTC Aspartate Mitochondrion T ASS Cytosol Urea Ornithine Cycle Argininosuccinate

Urea ASL Arginase Arginine T = Ornithine transporter Fumarate Fig. 181.1. The urea cycle. CPS1, carbamylphosphate synthase; NAGS, N-acetylglutamate synthase; OTC, ornithine transcarbamylase; ASS, argininosuccinate synthase; ASL, argininosuccinate lyase; T, ornithine transporter. (Adapted with permission from Zschocke and Hoffmann 2011.) DEFECTS IN AMINO ACID CATABOLISM AND THE UREA CYCLE 1757

Fig. 181.2. A 13-day-old child with citrullinemia revealed by coma and hyperammonemia. MRI (T1) shows bilateral insular and perirolandic cortical hypersignal. (Courtesy of Professor Boddaert.) images and elevated choline/creatine ratios and abnor- cellular transport including transporter proteins for the mal peak at 3.8 ppm, most likely representing arginine dibasic amino acids ornithine (HHH syndrome) and deposition (Gung€ or€ et al., 2008). Centropontine myelino- aspartate (citrullinemia II) primarily result in neurolog- lysis has also been reported (Mattson et al., 1995). Brain ical disease. relies on energy-dependent glutamine synthesis by astro- Onset of symptoms may occur at any age; however, it cytic glutamine synthase for the removal of excess NH3. is particularly frequent during the neonatal period, in As a consequence, increased brain NH3 is considered to late infancy, and in puberty, and is precipitated by excess amplify glutamatergic signaling, redistribution of cere- protein or episodes that induce catabolism such as infec- bral blood flow and metabolism, impairment of brain tious diseases, trauma, or steroid therapy. Neonatal pre- energy metabolism affecting the glutamate/glutamine sentation starts after a short asymptomatic interval with cycle, and increased serotonin secretion. Hyperammone- poor feeding, vomiting, lethargy, tachypnea and/or irri- mia exerts reversible (mostly serotonergic) as well as tability which cannot be distinguished clinically from irreversible effects. All inherited UCD follow an autoso- neonatal sepsis. Untreated, acute encephalopathy rap- mal recessive trait except for ornithine transcarbamylase idly progresses to death. In infancy, the symptoms are deficiency which is X-linked. less acute and more variable than in the neonatal period including anorexia, vomiting, developmental delay, and behavioral problems. In X-linked ornithine transcarba- CLINICAL PRESENTATION mylase deficiency, female carriers may also be affected UCDs are among the most common IEM (cumulative due to variable inactivation of X-chromosome (Lyon incidence approx. 1:30000 newborns). Six inherited hypothesis). Clinical presentation ranges from acute UCDs are well described, i.e., deficiencies of hepatic failure, progressive cognitive deficits, and N-acetylglutamate synthase, carbamoyl phosphate behavioral problems to psychiatric disease. In arginase synthetase 1, ornithine transcarbamylase, argininosuc- deficiency, patients usually present with progressive cinate synthetase, and lyase, and arginase 1. Five UCDs spasticity which is often mistaken as cerebral palsy, sei- share a common but variable clinical presentation due to zures, and mental defect. Dystonia and ataxia may hyperammonemia. Arginase deficiency and defects of develop. Acute decompensations are rarely found in this 1758 G.F. HOFFMANN AND S. KO¨ LKER

Fig. 181.3. A 23-month-old child with ornithintranscarbamylase deficiency revealed by neonatal coma. MRI (FLAIR) shows white matter hypersignal on pyramidal tract and external capsule, and atrophy at the depth of the sylvian fissure and bilateral caudate hypersignal. (Courtesy of Professor Boddaert.) disease. However, stroke-like events have been reported significant health problem and are accompanied with a in early childhood (Mamourian and du Plessis, 1991) high morbidity and mortality, genetic counseling should (Fig. 181.3), and centropontine myelinolysis that was be provided to high risk families. revealed in a 5-year-old boy by intractable seizures and coma several days following correction of hyperammo- THERAPY AND OUTCOME nemia (Mattson et al., 1995). The aim of treatment is to ensure normal growth and development, to prevent cerebral injury, and to DIAGNOSIS correct the biochemical disorder (glutamine in plasma Emergency analysis of ammonia must be part of the <800–1000 mmol/L, ammonia<80 mmol/L, arginine basic investigations in all patients at all ages with unclear 80–150 mmol/L) (Blau et al., 2005). The major metabolic encephalopathy, nonspecific “encephalitis,” or acute strategies are: (1) reduction of natural protein to hepatic failure. Blood gas analyses and anion gap char- decrease ammonia production, (2) supplementation with acteristically show alkalosis and normal anion gap in essential AAs to prevent malnutrition and to reutilize UCDs and acidosis and increased anion gap in OADs. nitrogen for the synthesis of nonessential AAs, (3) Characteristic biochemical changes (glutamine, alanine, replacement of arginine or citrulline, and (4) utilization citrulline, ornithine, arginine, argininosuccinic acid, oro- of alternative pathways for nitrogen excretion. The latter tic acid) can be identified by analysis of plasma AAs, uri- include application of sodium benzoate (250–500 mg/ nary organic acids, or orotic acid, uracil, and orotidine. kg/day) and sodium phenylbutyrate or phenylacetate The diagnosis must be confirmed by enzyme analysis in (250–600 mg/kg/day) to achieve urinary excretion of liver tissue (all UCDs except for N-acetylglutamate waste nitrogen in alternative compounds (hippurate, synthase deficiency), fibroblasts (argininosuccinate syn- phenylacetylglutamine). In N-acetylglutamate synthase thetase and lyase), or molecular genetic studies. Prenatal deficiency, N-carbamylglutamate can be used as alterna- diagnosis is feasible. Since UCDs in general cause a tive allosteric activator of carbamoylphosphate DEFECTS IN AMINO ACID CATABOLISM AND THE UREA CYCLE 1759 synthase. A partial response to N-carbamylglutamate (Zinnanti et al., 2009). In neonatal screening programs has also been described in some patients with carbamoyl- a prevalence of approximately 1:200000 newborns is phosphate 1 synthetase deficiency. Liver transplant may encountered (Schulze et al., 2003) but in the Mennonites be considered as the best treatment option especially for in Pennsylvania the prevalence is as high as 1:200. neonatal-onset patients. Patients with UCDs are always at risk of peracute Clinical presentation metabolic decompensations precipitated by metabolic Four different clinical presentations of the disease have stress such as protein load, infection, anesthesia, or sur- been delineated with overlap for individual patients: gery (Prietsch et al., 2002). The main factors that deter- (1) classic MSUD presenting in the newborn period, mine outcome are not fully clear but duration and (2) intermittent MSUD with recurrent episodes of neuro- severity of hyperammonemia are considered most logical presentations precipitated by intercurrent ill- important. Rapid diagnosis and immediate start of treat- nesses, (3) intermediate MSUD with progressive ment after the onset of first symptoms are crucial. Coma failure to thrive, developmental delay, autistic features, lasting more than 2–3 days and very high ammonia seizures, and dystonia, and (4) thiamin-responsive levels> 1000 mmol/L are associated with irreversible MSUD. Most patients with MSUD suffer from the clas- neurological defects; however, recovery from hyper- sic form. If untreated, these neonates quickly deteriorate ammonemic crises shows a significant variation within with lethargy and hypotonia alternating with muscular affected individuals. Outcome clearly depends not only rigidity, opisthotonic posturing and seizures. Neuroim- on ammonia but also on cerebral glutamine levels and is aging shows localized or diffuse generalized cerebral therefore difficult to predict in the acute presentation. edema, delayed myelin maturation, and symmetrical sig- Furthermore, the prognosis in UCDs is negatively corre- nal abnormality within the globi pallidi, midbrain, dorsal lated to the onset of first symptoms, i.e., patients with pons, and medulla (Ben-Omran et al., 2006; Bindu et al., neonatal onset have the highest rate of mortality and 2007)(Fig. 181.5). Convulsions appear regularly, and severe disability. EEG reveals abnormalities with comb-like rhythms Epilepsy in children with UCDs should not be treated (5–9 Hz) of spindle-like sharp waves over the central with valproate since this treatment may increase the risk regions and multiple shifting spikes and sharp waves for hyperammonemia and hepatic failure (Oechsner with suppression bursts. Prominent neuropathological et al., 1998). If valproate is used, carnitine supple- signs of untreated MSUD are cerebral edema (Sutter mentation should also be instituted. Valproate-induced et al., 2009) followed by atrophy and white matter abnor- hyperammonemia is considered to be associated with malities. Hypodensities may be present in globus palli- hypocarnitinemia induced by sodium benzoate treat- dus and thalamus. ment. Recently, it has been demonstrated that Patients with intermittent MSUD present with fluctu- valproyl-CoA directly inhibits N-acetylglutamate ating neurological disease such as lethargy, ataxia, and synthase resulting in at least transiently impaired pro- seizures that may quickly progress to coma and death duction of N-acetylglutamate, the cofactor of carbamyl- during episodes of catabolic stress such as intercurrent phosphate synthetase 1 (Aires et al., 2010). infections or surgery/anesthesia. Disturbances of consciousness revealing decompensation may be combined Defects of branched-chain amino acid with hallucinations (Holmgren et al., 1980). The interme- metabolism diate MSUD variant is characterized by failure to thrive MAPLE SYRUP URINE DISEASE and progressive mental defect. In a few patients, mostly with intermittent or intermediate variants, the metabolic In MSUD, the branched-chain AAs leucine, isoleucine, defect can be corrected by thiamin (thiamin- and valine, their corresponding a-keto acids and hydroxy responsive variant). Effective thiamin doses vary con- acid derivatives as well as L-alloisoleucine accumulate siderably, i.e., from 10 mg up to 300 mg per day. due to inherited deficiency of the thiamin-dependent branched-chain a-keto acid dehydrogenase complex. Diagnosis L-alloisoleucine results from racemization of the 3-carbon of L-isoleucine during transamination. Its elevation is Presumptive diagnosis can be made when the odor of pathognomomic for MSUD (Fig. 181.4). In an animal maple syrup is present (most intensively in the ear). Diag- model, there were two mechnisms for brain dysfunction: nosis is confirmed by detection of increased plasma con- neurotransmitter deficiencies and growth restriction centrations of leucine, isoleucine, and valine and/or by associated with branched-chain amino acid accumulation, increased urinary excretion of a-keto and hydroxy acids. and energy deprivation through Krebs cycle disruption The detection of L-alloisoleucine is pathognomonic. associated with branched-chain keto acid accumulation Reduced enzyme activity can be demonstrated in 1760 G.F. HOFFMANN AND S. KO¨ LKER Valine Isoleucine Leucine

Aminotransferase Aminotransferase Aminotransferase

Alloisoleucine 2-Oxo- 2-OH- 2-Oxo- 2-Oxo- 2-Oxoisocaproate isovalerate isovalerate 3-methylvalerate isocaproate 2-OH-isocaproate

BCKDH BCKDH BCKDH

Isobutyryl-CoA 2-Methylbutyryl-CoA Isovaleryl-CoA 3-OH-isovalerate Isovalerylglycine IBD MBD IVD

Tiglyl- Methylacrylyl-CoA Tiglyl-CoA 3-Methyl- 3-OH-isovalerate glycine crotonyl-CoA 3-Methylcrotonyl- Hydratase Hydratase glycine MCC

3-OH-isobutyryl-CoA 2-Methyl- 3-OH-butyryl-CoA 3-Methyl- 3-Methylglutarate Deacylase glutaconyl-CoA MHBD Hydratase 3-OH-isobutyrate 2-Methyl- DH acetoacetyl-CoA 3-OH-3-methylglutaryl-CoA 3-Oxothiolase Methylmalonate HMG-CoA lyase semialdehyde DH

Propionyl-CoA Acetyl-CoA Acetoacetate

Carboxylase 3-OH-propionate Methylcitrate Methylmalonyl-CoA Mutase Krebs cycle Succinyl-CoA Fig. 181.4. Metabolism of branched-chain amino acids. BCKDH, branched chain a-keto acid dehydrogenase (deficient in MSUD); IVD, isovaleryl-CoA dehydrogenase (deficient in isovaleric academia); MCC, 3-methylcrotonyl-CoA carboxylase (deficient in methylcrotonylglycinuria); hydratase, 3-methylglutaconyl-CoA hydratase (deficient in 3-methylglutaconic aciduria type I); MHBD, 2-methyl-3-hydroxybutyryl-CoA dehydrogenase (deficient in 2-methyl-3-hydroxybutyryl-CoA dehydrogenase deficiency); DH, dehydrogenase; PCC, propionyl-CoA carboxylase (deficient in propionic aciduria); MCM, methylmalonyl CoA mutase (deficient in methylmalonic aciduria). Accumulating pathological metabolites are shown in italics. (Adapted with permission from Zschocke and Hoffmann 2011.) leukocytes, lymphoblasts, cultured fibroblasts, or amnio- parallel, branched-chain AA-free supplements should cytes. Except for the common Mennonite mutation, the be administered by nasogastric drip feeding. Extra- molecular base of MSUD is complex. corporeal detoxification (hemodialysis, hemofiltration) may be required if leucine levels exceed 20 mg/dL (1500 mmol/L). Treatment and outcome Long-term treatment of MSUD is based on dietary In MSUD, the major aim of emergency treatment is the restriction of branched-chain AAs and supplementation rapid reduction of branched-chain AAs, particularly leu- of thiamin, if proven beneficial. Management in MSUD cine (Blau et al., 2005). To induce anabolism, high calorie requires very close and lifelong regulation of diet intake is required. Glucose stimulates endogenous insu- (Morton et al., 2002; Hoffmann et al., 2006). Liver trans- lin secretion activating protein synthesis. If required, plant may be considered as a reasonable treatment insulin administration should be started early. In option for patients with classical MSUD. DEFECTS IN AMINO ACID CATABOLISM AND THE UREA CYCLE 1761

Fig. 181.5. A 29-day-old child with maple syrup disease revealed by coma. MRI (T2) shows sub- and supratentorial white matter hypersignal, namely affecting posterior capsules, thalami, brainstem, and dentate nuclei. (Courtesy of Professor Boddaert.)

Children with the classic form of MSUD have only a may lead to coma and death, the other half with chronic satisfactory prognosis, if they are diagnosed and treated intermittent disease consisting of episodes of metabolic before neonatal onset of symptoms and thus MSUD has acidosis and developmental delay. Both phenotypes can been implemented into MS/MS-based newborn screen- occur within the same family suggesting a modifying ing in some countries (Schulze et al., 2003). role of environmental and epigenetic factors. A mild, potentially asymptomatic phenotype exists due to a com- ISOVALERIC ACIDURIA mon mutation (c.932C>T; p.Ala282Val). This mutation was detected in one half of mutant alleles in patients Isovaleric aciduria is caused by deficiency of isovaleryl- identified by newborn screening and also in older, CoA dehydrogenase, an enzyme located proximally in healthy siblings. the catabolic pathway of the essential branched-chain During metabolic crisis, patients present with the typ- AA leucine. Described by Tanaka and colleagues in ical features of classical OADs, i.e., acidosis, ketosis, 1966, isovaleric aciduria was the first OAD identified. vomiting, progressive alteration of consciousness, and, Due to the metabolic block, isovaleryl-CoA accumulates, finally, overwhelming illness, deep coma, and death and the pathognomonic metabolite isovalerylglycine is without appropriate therapy. Clinical abnormalities formed. It is suggested that accumulating acyl-CoA often develop within the first days of life. A foul odor esters impair mitochondrial energy metabolism and reminiscent of “sweaty feet” caused by isovaleric acid ammonia detoxification causing lactic acidosis and has been described and is rather pathognomonic. Abnor- hyperammonemia. Furthermore, isovaleric acid inhibits malities of the hematopoietic system such as thrombocy- granulopoietic progenitor cell proliferation which may topenia, neutropenia, or pancytopenia develop during explain neutropenia during metabolic decompensations. metabolic decompensation. Hyperammonemia is usually mild, compared with other OADs. Clinical presentation In the chronic intermittent form, children slide into Half of the patients with isovaleric aciduria present in recurrent metabolic crises because of high intake of the neonatal period with severe metabolic crisis that protein or catabolic state. Hematological abnormalities 1762 G.F. HOFFMANN AND S. KO¨ LKER develop as described above, and hyperglycemia may MCC is a genetic condition with low clinical expressivity develop, most likely due to stress-induced counter- and penetrance, presenting largely (approximately 90%) regulatory hormonal effects. Pancreatitis may be a com- as a nondisease. Fewer than 10% of affected individuals plication of acute and chronic isovaleric aciduria. may develop mostly mild neurological symptoms which are often not clearly attributed to MCC deficiency. Diagnosis However, a few patients may develop acute metabolic decompensation (ketoacidosis, hypoglycemia, hyperam- During metabolic decompensation, the urinary organic monemia, Reye-like syndrome) precipitated by febrile ill- acid profile reveals high excretion of isovalerylglycine ness during infancy which may even be fatal if untreated. which remains elevated in stable metabolic conditions. 3-Hydroxyisovaleric acid only increases during meta- Diagnosis bolic decompensation. Isovalerylcarnitine is the characteristic acylcarnitine of this disease; its urinary excretion As a consequence of MCC deficiency, increases following supplementation with L-carnitine. 3-hydroxyisovaleric acid, 3-hydroxyisovalerylcarnitine, The diagnosis can be confirmed by enzyme or mutation 3-methylcrotonylcarnitine and -glycine accumulate. Nor- analysis. malization of 3-hydroxyisovalerylcarnitine concentrations in follow-up investigations of any neonate should Treatment and outcome prompt the investigation of MCC deficiency in the mother. If additional metabolic abnormalities (e.g., lac- Total natural protein intake is restricted according to the tic acidosis, 2-methylcitrate, 3-hydroxypropionate, pro- patient’s leucine tolerance and is adjusted to age-specific pionylcarnitine and -glycine) are found, multiple requirements. To provide a complementary source of the carboxylase deficiency and biotinidase deficiency other AAs, a leucine-free formula is available. Urinary should be considered. excretion of isovaleryl-CoA is activated by supplementation with carnitine (50–100 mg/kg per day) and glycine Treatment and outcome (150–600 mg/kg per day). Prompt initiation of emergency treatment during Most affected individuals do not require specific treat- acute decompensation is most important (Prietsch ment with the exception of carnitine supplementation if et al., 2002). Aspirin is contraindicated because salicylic severe secondary carnitine depletion is found. MCC acid is a competing substrate for glycine-N-acylase, deficiency is usually unresponsive to biotin. Most interfering with isovalerylglycine synthesis. affected individuals remain asymptomatic without spe- Efficient treatment before the occurrence of any cific treatment and thus MCC deficiency has been omit- severe metabolic decompensation will significantly ted from the newborn screening disease panel in many improve the patient’s prognosis. In some countries isova- countries. leric aciduria has become included in extended newborn screening programs with good outcomes (Schulze et al., 3-METHYLGLUTACONIC ACIDURIAS 2003). Older patients may have normal psychomotor Increased urinary excretion of 3-methylglutaconic acid development or mild to severe mental defect, depending is the biochemical hallmark of a heterogeneous group on the frequency of metabolic decompensations and age of IEM termed 3-methylglutaconic acidurias. Increased at diagnosis. urinary concentrations of 3-methylglutaconic acid is frequently seen in ATPase related mitochondrial disorders 3-METHYLCROTONYLGLYCINURIA but not in patients with single respiratory chain complex 3-Methylcrotonylglycinuria is an inborn error of leucine deficiencies (Wortmann et al., 2013). catabolism due to deficiency of 3-a-methylcrotonyl-CoA carboxylase (MCC). It appears to be the most frequent 3-Methylglutaconic aciduria type I OAD with an overall prevalence of approximately 1 in 3-Methylglutaconic aciduria type I is caused by inher- 50000 newborns (Schulze et al., 2003). The MCC ited deficiency of 3-methylglutaconyl-CoA hydratase enzyme requires biotin as a cofactor, and the isolated required for the conversion of 3-methylglutaconyl- enzymatic defect must be differentiated from primary CoA to 3-hydroxy-3-methylglutaryl-CoA in leucine deficiencies in the biotin pathway. catabolism. The hydratase is identical to a RNA- binding protein (designated AUH) possessing enoyl- Clinical presentation CoA hydratase activity. The defect leads to an Based on follow-up of individuals identified by newborn accumulation of 3-methylglutaconic, 3-methylglutaric, screening, it has become evident that deficiency of and 3-hydroxyisovaleric acids. DEFECTS IN AMINO ACID CATABOLISM AND THE UREA CYCLE 1763 Clinical presentation. The clinical phenotype of Biochemically, increased 3-methylglutaconic acid is affected individuals is variable and includes asymp- usually found in urine but is not a constant feature. tomatic disease course. Patients may present with 2-Ethylhydracrylic acid may be also elevated. Muscle neurological symptoms including delayed speech and disease and lactic acidemia may initiate a work-up for motor development. Metabolic decompensation during mitochondrial disorders. Muscle biopsy may reveal catabolic state with hypoglycemia and metabolic involvement of deficient respiratory chain complex I acidosis is rare. and IV. The diagnosis is confirmed by cardiolipin anal- Diagnosis. Urinary excretion of large amounts ysis in thrombocytes or mutation analysis. Mutation of 3-methylglutaconic, 3-methylglutaric, and 3- analysis makes prenatal diagnosis now available. hydroxyisovaleric acids but normal excretion of Treatment and outcome. Children affected by Barth 3-hydroxy-3-methylglutaric acid pinpoint to hydratase syndrome need to be carefully managed by expert cardi- deficiency. Increased 3-hydroxyisovalerylcarnitine, ologists with the involvement of immunologists and detectable in extended newborn screening, is a hint for neurologists. Dysrhythmias are a dubious sign and either type of 3-methylglutaconic aciduria. The defini- may require implantation of an internal cardiac defibril- tive diagnosis is made by enzyme analysis in fibroblasts lator. Successful heart transplantation has been per- or by mutation analysis. formed in one child. Due to increased susceptibility to Treatment and outcome. The need for treatment has severe bacterial infections, infectious diseases need to not been established, especially not for dietary treat- be treated promptly and aggressively. Protein restriction ment. The outcome appears favorable, as a significant and carnitine supplementation has been employed with number of patients have never developed symptoms unclear benefit. About 25% of patients with Barth syn- without treatment. drome succumb during infancy and early childhood due to cardiac complications or overwhelming bacterial infections. 3-Methylglutaconic aciduria type II – Barth syndrome 3-Methylglutaconic aciduria type III – Costeff The molecular base of Barth syndrome is deficiency of syndrome tafazzin localized in the inner mitochondrial membrane Costeff syndrome is caused by mutations in the OPA3 affecting phospholipid metabolism, in particular cardio- gene resulting in a defect of a putative mitochondrial lipin. The origin of elevated levels of 3-methylglutaconic protein with yet unknown function. The origin of ele- and 3-methylglutaric acids is unknown. The identifica- vated levels of 3-methylglutaconic and 3-methylglutaric tion of the causative gene allowed the retrospective clas- acids is also unknown. So far the disorder has only been sification of different families labeled in the past as reported in Iraqi Jews. X-linked endocardial fibrosis, severe X-linked cardio- Clinical presentation. The determining clinical pre- myopathy, or Barth syndrome. sentation is infantile optic atrophy which may be accom- Clinical presentation.In1983, Barth and colleagues panied by nystagmus. About half of the patients develop described an X-linked neuromuscular disease character- spastic paraparesis during the second decade of life. ized by dilated cardiomyopathy with characteristic isolated Ataxia and cognitive deficits are common, usually of left ventricular noncompaction, skeletal myopathy, mild degree. retarded growth and neutropenia. Patients may present Diagnosis. Costeff syndrome should be suspected at birth or during the first weeks of life, usually with in patients presenting with infantile optic atrophy, congestive cardiac failure. With longstanding cardiac if additional neurological symptoms develop. disease endocardial fibroelastosis may develop. 3-Methylglutaconic aciduria is a biochemical indicator Delayed gross motor milestones, myopathic facies, a of Costeff syndrome which may now be proven by waddling gait, and a positive Gower’s sign are common. molecular analysis. Occasionally patients may show moderate lactic Treatment and outcome. Treatment is symptomatic acidosis. Postnatal growth retardation may be severe, and focuses on the prevention of disabilities due to pro- and beyond 2 years of age patients usually grow 3–5 gressive spasticity. The disease appears stationary but standard deviations below normal, but with a normal head the long-term outcome is unknown. circumference. Diagnosis. Barth syndrome should be considered in 3-Methylglutaconic aciduria type IV – unclassified any male presenting with dilated cardiomyopathy. If isolated left ventricular noncompaction, neutropenia, idio- 3-Methylglutaconic aciduria type IV is surely hetero- pathic myopathy, or growth retardation are also present, geneous. As unexplained 3-methylglutaconic aciduria, the diagnosis of Barth syndrome is almost certain. i.e., type IV, was also found incidentally in asymptomatic 1764 G.F. HOFFMANN AND S. KO¨ LKER adults, it appears doubtful that this biochemical feature by Neuroimaging documents progressive generalized atro- itself is of pathophysiological relevance. phy, basal ganglia injury, periventricular white matter Clinical presentation. Neurological symptoms are abnormalities, and occipital infarctions in individual predominant but variable including motor and mental cases. Heterozygous female patients may be asymptom- defect, spasticity, hypotonia, optic atrophy, deafness, atic or may have variable stationary psychomotor retar- and seizures. MRI studies revealed brain atrophy, basal dation with impaired hearing. ganglia injury, and/or cerebellar atrophy. Recently, 3-methylglutaconic aciduria with neonatal encephalo- Diagnosis myopathy due to ATP synthase deficiency (TMEM70) The disease should be considered in children presenting and 3-methylglutaconic aciduria with sensorineural with early-onset progressive encephalopathy, especially, deafness, encephalopathy, and Leigh-like syndrome if X-linked inheritance is suggested. The biochemical (MEGDEL association) was delineated suggesting two hallmark of this disease is increased urinary excretion additional specific clinical entities (Wortmann et al., of 2-methyl-3-hydroxybutyric acid and tiglyglycine. 2006, 2009). In contrast, 3-methylglutaconic aciduria Elevations of 2-ethylhydracrylic acid and was also identified in asymptomatic individuals. 3-hydroxyisobutyric acid in urine may also be found. Diagnosis. Patients are identified by elevated The diagnosis is confirmed by hemizygous mutations urinary concentrations of 3-methylglutaconic and 3- in the HSD17B10 gene. methylglutaric acids. Classification of type IV methylglutaconic aciduria is made by exclusion of known Treatment and outcome causes of 3-methylglutaconic aciduria (types I–III; see above), primary mitochondrial disorders (e.g., Pearson Care of patients with this disease should repeatedly syndrome), and Smith–Lemli–Opitz syndrome. entail: (1) assessment of muscle and cardiac function; Treatment and outcome. Treatment is symptomatic (2) neurological examination including EEG and MRI; and focuses on the prevention and management of and (3) assessment of visual and hearing system. The neurological disease. prognosis is mostly poor if first symptoms occur during the newborn period or early infancy, with death occur- 2-METHYL-3-HYDROXYBUTYRYL-COA ring in early childhood. DEHYDROGENASE DEFICIENCY PROPIONIC ACIDURIA 2-Methyl-3-hydroxybutyryl-CoA dehydrogenase (syno- nym, 17-b-hydroxysteroid dehydrogenase 10) deficiency Propionyl-CoA is formed from the catabolism of isoleu- is a very rare cerebral OAD. This mitochondrial enzyme cine, threonine, methionine, valine, odd-numbered fatty is involved in the catabolism of isoleucine and branched- acids, the side chain of cholesterol, and from gut bacte- chain fatty acids, and is identical to an amyloid b- ria. Deficient propionyl-CoA carboxylase (PCC) gives peptide-binding protein which is involved in Alzheimer rise to accumulation of metabolites deriving from alter- disease. Retrospectively, patients were misdiagnosed native oxidation of propionyl-CoA as well as its conjuga- as suffering from 3-oxothiolase deficiency until tion with glycine and carnitine. Elevated propionyl-CoA Zschocke and colleagues (2000) recognized the separate and its pathological derivatives interfere with a variety distinct clinical and biochemical presentation. Inheri- of metabolic pathways including inhibition of mitochon- tance is X-chromosomal semidominant (females may drial energy metabolism and ammonia detoxification be symptomatic). The disease is caused by mutations resulting in lactic acidemia and hyperammonemia. in the HSD17B10 gene which is located on Xp11.2. Clinical presentation Clinical presentation Propionic aciduria frequently presents with severe neo- Male patients with a fatal disease course may present natal metabolic decompensation characterized clinically with hypoglycemia, metabolic acidosis, and lactic acide- by multiorgan failure and biochemically by hyperammo- mia within the first hours of life. The remaining patients nemia, metabolic acidosis, hyperketosis, lactic acidemia, present over a range of 9 months to 6 years of age hyperglycinemia, and hyperalaninemia. Neonatal onset (Zschocke et al., 2000; Perez-Cerda et al., 2005). The of propionic aciduria may be misinterpreted as sepsis most common clinical symptom is speech delay. Visual or ventricular hemorrhage and thus some patients may and hearing alterations, muscular hypotonia with spas- die undiagnosed. Acute metabolic decompensation ticity of the limbs, dyskinesia and athetosis, and epilepsy and long-term complications usually involve organs with are other common symptoms. Motor and mental skills a high energy demand, including the brain, heart, and are progressively lost, as are sensory modalities. skeletal muscle, liver, and bone marrow. Signs and DEFECTS IN AMINO ACID CATABOLISM AND THE UREA CYCLE 1765 symptoms of chronic disease are failure to thrive, micro- reach adulthood but are often neurologically handi- cephaly, mild to severe motor and mental defect, truncal capped. Individual patients can develop intellectually hypotonia, extrapyramidal symptoms (dystonia, normal into adult life. chorea), seizures, cardiomyopathy, myopathy, hepato- 0 megaly, acute or chronic pancreatitis, leukopenia, METHYLMALONIC ACIDURIA (MUT , MUT ) thrombocytopenia, anemia, or pancytopenia, whereas renal complications are uncommon. Metabolic decom- Methylmalonic aciduria is the biochemical hallmark of a pensations in infancy or childhood are similar to those heterogeneous group of IEM with a cumulative preva- in the neonatal period. The first symptom is often vomit- lence of at least 1:100000 newborns in Europe. This ing. Basal ganglia injury, mostly affecting the putamen chapter focuses on isolated methylmalonic aciduria with major dystonia or choreic movements, is frequently caused by mutations in the MUT gene encoding found after severe metabolic decompensations. In addi- methylmalonyl-CoA mutase (MCM). MCM can alterna- tively be impaired by defects in the biosynthesis of tion, neuroimaging often demonstrates generalized 0 cerebral atrophy and white matter abnormalities. 5 -deoxyadenosylcobalamin, by deficient cobalamin transport, or by acquired cobalamin deficiency such as Diagnosis pernicious anemia. In infancy, severe progressive disease may develop in breastfed infants of mothers suffer- Diagnosis is best accomplished by analysis of organic ing from (undiagnosed) pernicious anemia or mothers acids (urine) or of acylcarnitines (dried blood spots, adhering to a strict vegan diet. Methylmalonic acid is a plasma, urine). Characteristic metabolites are more reliable index of body stores of cobalamin than 2-methylcitric acid, 3-hydroxypropionic acid, propionyl- cobalamin levels in blood. In analogy to propionic acid- glycine, and propionylcarnitine. The absence of uria, MCM deficiency results in an accumulation of methylmalonic acid excludes methylmalonic acidurias, metabolites deriving from propionyl-CoA. Furthermore, and the absence of b-hydroxyisovaleric acid and name-giving methylmalonic acid accumulates. b-methylcrotonylglycine rules out multiple carboxylase Propionyl-CoA, methylmalonic acid, and 2-methylcitric deficiency. Increased concentrations of glycine and acid induce impairment of mitochondrial energy metab- ketone bodies may be present. Confirmation of diagno- olism and ammonia detoxification. sis is made by enzyme or mutation analysis. Prenatal diagnosis is possible. Clinical presentation 0 Treatment and outcome Patients with severe MCM deficiency (mut ) usually present with neonatal metabolic crises which are clinically Prevention of metabolic decompensation is the most and biochemically (except for methylmalonic acid) indis- important determinant of outcome. In analogy to iso- tinguishable from propionic aciduria (see above). In valeric aciduria and other OADs, prompt initiation of patients with residual MCM activity (mut), the onset emergency treatment during acute decompensation is of symptoms is more variable. Neonatal onset of symp- most important (Prietsch et al., 2002). Long-term treat- toms is found, as is chronic intermittent presentation, ment is based on lifelong dietary restriction of precursor i.e., precipitation of recurrent metabolic crises in infancy AAs, i.e., isoleucine, valine, methionine, and threonine, and children following high intake of protein or catabolic as well as by supplementation with L-carnitine (Blau state. Long-term complications are frequent, in particu- et al., 2005). As significant propionate production lar in mut0 patients. These include failure to thrive, occurs in the gut, intermittent decontamination (10–14 chronic neurological symptoms such as extrapyramidal days/month) with metronidazole or colistin, as well as movement disorder, motor and mental defect, and epi- measures preventing constipation, are useful. Some lepsy, including infantile spasms, cardiomyopathy, patients exhibit recurrent or almost chronic hyperammo- myopathy, pancreatitis, and chronic renal failure. Neu- nemia, especially during infancy. This may necessitate roradiological studies demonstrate lesions of globus pal- additional supplementation with arginine or citrulline lidus, generalized cerebral atrophy, and white matter and/or administration of sodium benzoate or phenylbu- disease (Fig. 181.6). tyrate. Biotin responsiveness in propionic aciduria is very rare – if present at all. Close to 20 children with Diagnosis propionic aciduria have undergone orthotopic liver transplantation. The outcome, however, has been As with other OADs, the best way to accomplish the disappointing. diagnosis is analysis of urinary organic acids or of acyl- Patients with neonatal onset of symptoms still have a carnitines (plasma, dried blood spots). Differential diag- poor outcome. Patients with late-onset of symptoms nosis of methylmalonic aciduria is acquired cobalamin 1766 G.F. HOFFMANN AND S. KO¨ LKER Cerebral organic acid disorders

GLUTARIC ACIDURIA TYPE I

Glutaric aciduria type I (GA-I), first described by Goodman and colleagues in 1975, occurs with an overall frequency of 1:100000 newborns. It is caused by deficiency of glutaryl-CoA dehydrogenase (GCDH), a mitochondrial key enzyme in the catabolic pathways of lysine, tryptophan, and hydroxylysine. GCDH deficiency results in accumulation of glutaric, 3-hydroxyglutaric and (inconsistently) glutaconic acids as well as of glutarylcarnitine. Due to the limited permeability of the blood– brain barrier to dicarboxylic acids (such as glutaric acid), these strongly accumulate in the brain (“trapping hypothesis”). Noteworthy, some of these metabolites are considered as neurotoxins.

Clinical presentation Newborns are often asymptomatic but may present with transient and subtle neurological symptoms such as trun- Fig. 181.6. A 6-year-old child with methylmalonic aciduria. MRI (T2) shows bilateral pallidal lesions. (Courtesy of Pro- cal hypotonia or asymmetric posturing. (Progressive) fessor Boddaert.) macrocephaly is found in 75% of patients. Neuroimag- ing in infancy often reveals hypoplasia of the temporal pole, subependymal pseudocysts, and delayed myelina- depletion or inherited cobalamin deficiencies, transient tion (Fig. 181.7). In addition, subdural fluid collections mild methylmalonic acidurias of unknown origin in may be found which may be mistaken as nonaccidental infants, and methylmalonic encephalopathy due to defi- trauma. ciency of succinyl-CoA synthase. Concomitant megalo- The prognostically relevant event of glutaric aciduria blastic anemia and an increase of plasma homocysteine type I is the onset of acute encephalopathic crises and, hint at a primary disturbance of cobalamin metabolism. subsequently, striatal injury precipitated by catabolic The determination of MCM activity, mutation analy- state during infancy and early childhood. Striatal injury sis, or the investigation of labeled propionate incorpora- results in dystonia or chorea. In a subgroup of patients, tion following transfection by a vector containing cloned neurological symptoms occur without apparent crises. mutase cDNA in intact patients’ fibroblasts is required to These patients follow a chronic disease course and differentiate primary defects of MCM (mut0,mut) may develop the same neurological symptoms as the from primary defects of cobalamin metabolism and acutely injured children (insidious onset) or present with transport. Prenatal diagnosis is available. severe headaches, reduced fine motor skills, hand tremor, and ataxia in adolescence/adulthood (late onset). Neuroradiological abnormalities are frequently found Treatment and outcome including widening of the sylvian fissure, ventriculome- Metabolic maintenance and emergency treatment fol- galy, striatal lesions, and white matter abnormalities lows treatment principles for OADs in general and pro- (Harting et al., 2009). pionic aciduria in particular (Blau et al., 2005; Horster€ et al., 2007). In addition, substitution with cobalamin Diagnosis may be beneficial (except for mut0 patients). Movement disorders are difficult to treat. Baclofen GA-I should be suspected in patients with macrocephaly and diazepam as monotherapy or in combination should and an extrapyramidal movement disorder starting in be used as first-line drug treatment for focal and gener- infancy or childhood. Diagnosis is ascertained by detec- alized dystonia. West syndrome may occur in case of tion of glutaric and 3-hydroxyglutaric acids in organic basal ganglia damage, which raises therapeutic issues: acid analysis or of elevated glutarylcarnitine. Confirma- steroid treatment can be used as a last treatment option tion by enzymatic analysis or mutation analysis is advis- provided the metabolic condition is carefully monitored able. A subgroup of patients presents with a mild (Campeau et al., 2009). biochemical phenotype (low excretors) and thus may DEFECTS IN AMINO ACID CATABOLISM AND THE UREA CYCLE 1767 D-2-HYDROXYGLUTARIC ACIDURIA

D-2-Hydroxyglutaric aciduria is a rare autosomal reces- sively inherited cerebral OAD. Recently, the molecular base of this etiologically heterogeneous disease has been identified: D-2-hydroxyglutaric aciduria type I is caused by autosomal recessive deficiency of D-2-hydroxyglutarate dehydrogenase, a mitochondrial enzyme converting D-2-hydroxyglutarate to 2- oxoglutarate. The human D2HGDH gene is located on 2p25.3 (Struys et al., 2005). D-2-Hydroxyglutaric aciduria type II is caused by deficient mitochondrial iso- citrate dehydrogenase. Autosomal dominant germline mutations of the IDH2 gene located on 15q26.1 are the molecular origin of type II (Kranendijk et al., 2010).

Clinical presentation Patients with D-2-hydroxyglutaric aciduria type I and II exhibit variable phenotypes; there is no known genotype/ phenotype correlation. Children with the severe disease variant present with early-infantile-onset encephalopathy demonstrating a combination of epileptic encephalopathy, hypotonia, cerebral visual failure, and severe psychomotor retardation. Facial dysmorphism, macro- Fig. 181.7. Glutaric aciduria type 1 at the age of 10 months, fol- cephaly, and cardiomyopathy may also be present. Mod- lowing acute encephalopathic crisis. MRI shows increased T2 erately affected children follow a much milder clinical hyperintensity and atrophy of putamen and caudate. (Courtesy course with variable symptoms including mental defect, of Professor Boddaert.) hypotonia, and macrocephaly. Rarely, individuals remain almost asymptomatic, i.e., presenting only with mild pharmacosensitive epilepsy or even without neuro- be missed. Noteworthily, these patients have the same logical symptoms. risk for acute striatal injury if they remain undiagnosed Neuroimaging findings in the severely affected patient and untreated. Examination of carnitine status usually group show ventriculomegaly, enlarged subarachnoid reveals secondary carnitine depletion. Prenatal diagnosis spaces, subdural effusions, subependymal cysts, and is possible. white matter abnormalities. Recently, agenesis of the corpus callosum, bilateral involvement of the striatum, and cerebral artery infarctions were added to the spectrum. Treatment and outcome The major aim of treatment is the prevention of enceph- Diagnosis alopathic crises and neurological deterioration. Strict The biochemical hallmark of this disease is the accumu- adherence to the emergency protocol during intercurrent lation of D-2-hydroxyglutaric acid in all body fluids. illnesses is especially important (Blau et al., 2005; Demonstration of elevated levels of 2-hydroxyglutaric Heringer et al., 2010). For maintenance treatment, a acid must be followed up by differential quantitation combination of low lysine diet (until age 6 years) and car- of the two isomers L- and D-2-hydroxyglutaric acid. nitine supplementation is used. Riboflavin is of doubtful 2-Oxoglutaric acid and other TCA cycle intermediates benefit. The efficacy of antidystonic treatment is still are usually also elevated in urine. GABA and total pro- poor, as in other patients with secondary dystonia. Bac- tein concentrations may be elevated in CSF. Prenatal lofen, benzodiazepines, and trihexiphenidyl are widely diagnosis can be performed. used to treat dystonia. Botulinum toxin and intrathecal baclofen are valid additions. The efficacy of pallidotomy Treatment and outcome and deep brain stimulation is doubtful. If diagnosed pre- symptomatically, treatment prevents striatal injury in the No specific therapy exists to date. Severely affected chil- majority of patients (Kolker€ et al., 2006). Life expec- dren may die in infancy, while moderately affected tancy is strongly reduced following striatal injury. patients have a better prognosis up to an unimpaired life. 1768 G.F. HOFFMANN AND S. KO¨ LKER L-2-HYDROXYGLUTARIC ACIDURIA marking the first successful treatment of a genetic disorder and resulting in the concept of early diagnosis by The disease is caused by deficiency of the mitochondrial newborn screening and treatment. The worldwide over- enzyme L-2-hydroxyglutarate dehydrogenase converting all incidence of PKU is approximately 1:10000 with a L-2-hydroxyglutarate to 2-oxoglutarate. L-2-hydroxyglu- large national and ethnic variability. taric aciduria is an autosomal recessive disorder. Muta- PKU is an autosomal recessive disorder caused by a tions in the L2HGDH (C14orf160/duranin) gene located defect of phenylalanine hydroxylase which converts on 14q22.1 have been identified as causative. Phe into tyrosine. The cofactor is tetrahydrobiopterin (BH4), and thus hyperphenylalaninemia may be also Clinical presentation caused by genetic defects in the generation of BH4 (Fig. 181.8). Though the mechanisms are still not In the first 2 years of life, mental and psychomotor completely understood, the excess Phe is directly toxic development may be normal or slightly delayed. Febrile to the (immature) brain and indirectly reduces the syn- seizures, nonspecific developmental delay, and muscu- thesis of proteins and neurotransmitter due to its compe- lar hypotonia are first noticed before progressive ataxia, tition with large neutral amino acids at the blood–brain variable extrapyramidal and pyramidal signs, epilepsy, barrier. and progressive mental defect develop. By adolescence, patients are usually bedridden and severely mentally retarded (IQ 40–50). Patients have been reported who Clinical presentation developed malignant cerebral tumours. Neuroimaging is unique comprising a progressive loss of arcuate fibers, Untreated, PKU almost invariably causes severe mental progressive cerebellar atrophy, and signal changes in defect. At birth, however, newborns with PKU are globus pallidus and the dentate nuclei. asymptomatic since fetal Phe levels are normalized by the mother’s intact metabolism. After birth Phe levels quickly rise. Constitutional abnormalities (80–100% of Diagnosis patients), such as hypopigmentation of the skin and hair L-2-Hydroxyglutaric aciduria results in a rather homog- (fair) and iris (blue), develop rapidly due to impaired enous clinical picture and characteristic abnormalities on metabolism of melanin. Elevated phenylacetate neuroimaging. Clinical or neuroradiological suspicion should prompt analysis of urinary organic acids and dif- GTP ferentiation of L-2- and D-2-stereoisomers. Lysine is often increased both in plasma and CSF. Prenatal diag- GTPCH nosis is based on the analysis of L-2-hydroxyglutaric acid in amniotic fluid samples or molecular analysis. Neopterin PTPS

Treatment and outcome No specific therapy exists to date; however, partial neu- SR rological improvement has been described in individual patients receiving riboflavin. Epilepsy can generally be controlled by antiepileptic medications. Patients with BH4 L-2-hydroxyglutaric aciduria can be expected to reach PAH, adult life. DHPR TYH, TPH, PCD NOS Phenylketonuria BH2 Biopterin CLASSICAL PHENYLKETONURIA: PHENYLALANINE Fig. 181.8. Biopterin metabolism. BH4 is synthesized and HYDROXYLASE DEFICIENCY regenerated by five enzymes. BH4 is consumed as a cofactor in the hydroxylation of tyrosine and tryptophan as well as phe- Phenylketonuria (PKU) was first identified by Flling in nylalanine (see also PKU) and nitric oxide synthase (NOS). 1934 in several severely retarded individuals by deter- BH2, dihydrobiopterin. Relevant enzyme defects: GTPCH, mining urinary excretion of phenylpyruvic acid, which GTP cyclohydrolase; PTPS, 6-pyruvoyl-tetrahydropterin led to the previously used term phenylpyruvic oligophre- synthase; SR, sepiapterin reductase; DHPR, dihydropteridine nia. In 1953, Bickel and colleagues demonstrated that reductase; PCD, pterin carbinolamine dehydratase. (Adapted a phenylalanine (Phe)-restricted diet was beneficial, with permission from Zschocke and Hoffmann 2011.) DEFECTS IN AMINO ACID CATABOLISM AND THE UREA CYCLE 1769 excretion gives the urine an odor reminiscent of mice Treatment and outcome and can cause eczema. Delayed psychomotor development may become Because of active placental transport, the ratio of fetal to suspicious from the third month of life. It was estimated maternal Phe plasma levels is 1.5 to 1.7. Maternal Phe that one intelligence point is lost for each week of delay in values should be between 120 and 360 mmol/L, which diagnosis and treatment. Cognitive function is severely requires very careful monitoring twice weekly. Micro- compromised in untreated children (IQ< 40). Microceph- cephaly and congenital heart disease in the offspring aly and movement disorders are common, as are hyper- as of mothers returning to diet at the seventh or eighth week well as hypoexcitability and seizures, especially infantile led to the concept of preconception training and diet. spasms; some patients develop autistic behavior or Lowering maternal Phe levels during pregnancy to a level aggressiveness. MRI shows delayed myelination. Most between 120 and 360 mmol/L results in a favorable out- patients with untreated PKU cannot be managed by their come in virtually all cases (Koch et al., 2003). families and require institutional care. Defects of methionine and homocysteine Diagnosis metabolism In many countries, newborns are screened for increased The transsulfuration pathway transfers the sulfur of Phe levels in dried blood spots during the first days of methionine to serine to produce cysteine. Half of the life. The implementation of mass spectrometric tech- homocysteine formed goes through the transsulfura- niques has significantly improved the early identification tion pathway and the other half takes a methyl of affected individuals by newborn screening (Schulze group from betaine (betaine methyltransferase) or et al., 2003). 5-methyltetrahydrofolic acid (methionine synthase). The latter is a cobalamin-dependent enzyme which is Treatment and outcome functionally impaired in defects of cobalamin metabolism. The remethylation of homocysteine is also impaired The most important therapeutic intervention in PKU is if the activity of the reductase that generates Phe-restricted dietary treatment. Regular Phe determina- 5-methyltetrahydrofolate is inadequate (Fig. 181.9). tions are used for monitoring. Unfortunately, recom- Hyperhomocysteinemia of varying degree is the biochem- mendations for PKU treatment differ with regard to ical hallmark of all of these disorders. When accumulation cut-off levels to begin dietary treatment, age-dependent of homocysteine results from defects of homocysteine recommendations for Phe concentrations, frequency of remethylation plasma methionine concentrations are clinical examinations, and Phe monitoring. There is no low. They are high when homocysteine accumulates from rational explanation for this. impaired activity of cystathionine b synthase. When a very strict diet is begun early and well- maintained, affected children can expect normal devel- CLASSICAL HOMOCYSTINURIA: CYSTATHIONINE opment and life span. Regression of IQ when diets were b-SYNTHASE DEFICIENCY stopped in later childhood has led to continuation of dietary treatment into teenage years and adulthood. Most Clinical presentation recommendations and centers have adopted a philoso- phy of “diet for life.” Untreated classical homocystinuria is a slowly progressive devastating multiorgan disorder (Mudd et al., 1985). First symptoms in childhood are a rapidly progres- MATERNAL PHENYLKETONURIA sive myopia and lens dislocation. Lens dislocation usu- In 1980, Lenke and Levy highlighted severe adverse fetal ally occurs in preschool years, but later dislocation is effects of maternal hyperphenylalaninemia. The clinical well recognized in pyridoxine-responsive patients, and features are similar to the fetal alcohol syndrome, and a few have not developed it even in adult life. Monocular severity of the manifestations depends on the maternal and binocular blindness has been relatively frequent Phe level. In addition to mental defect and behavioral due to secondary glaucoma, staphyloma formation, disorders, they can include malformations such as car- buphthalmos, and retinal detachment. diac defects (usually conotruncal), vertebral malforma- In the older child skeletal abnormalities and mental tions, facial dysmorphic features (long underdeveloped defect become obvious. Genu valgum and pes cavus philtrum, broad nasal bridge, micrognathism, high pal- are usually the first signs of skeletal changes. They ate, divergent strabismus) as well as microcephaly, intra- include osteoporosis and spontaneous crush vertebral uterine growth retardation, neuronal migration fractures. The common abnormalities seen in Marfan disorders, and agenesis of the corpus callosum. syndrome – high arched palate, pectus excavatum or 1770 G.F. HOFFMANN AND S. KO¨ LKER Remethylation Methionine MAT THF

S-AdoMet DMG

MS B12 BMT GMT Folic acid MTHFR Betaine S-AdoHcy MeTHF S-AdoHcyH Homocysteine

CBS B6 Cystathionine

Transsulfuration γ Case Cysteine Fig. 181.9. Outline of methionine and homocysteine metabolism. BMT, betaine methyltransferase; g Case, gamma-cystathionase; CBS, cystathionine b-synthase; GMT, glycine methyltransferase; MAT, methionine adenosyltransferase; B12, methylcobalamin; MeTHF, 5-methyltetrahydrofolate; MTHFR, methylenetetrahydrofolate reductase; MS, methionine synthase; S-AdoHcy(H); S-adenosylhomocysteine (hydrolase); S-AdoMet, S-adenosylmethionine; THF, tetrahydrofolate. carinatum, genu valgum, pes cavus or planus, scoliosis – negative. Unfortunately, methionine elevation is unreli- are all well recognized in homocystinuria. Arachnodac- able in the early days of life, hampering newborn screen- tyly is less common and the fingers not infrequently (and ing. Confirmation of diagnosis can be performed by elbows occasionally) show mild flexion contractures. enzyme assay using cultured skin fibroblasts and/or muta- Skeletal disproportion with a crown pubis length less tion analysis. than the pubis heel length is usual. Mental defect affects two-thirds of patients. Patients responsive to pyridoxine Treatment and outcome (vitamin B6) (see below) generally have higher IQ values than nonresponsive patients. Seizures affect about one- Optimal outcome of treatment depends on the earliest fifth and a few patients show extrapyramidal features, possible introduction. Treatment is focused on normal- sometimes with severe involuntary movements. Psychi- izing homocysteine levels and needs to be followed vig- atric disturbances have also been described. orously for life. In about half of the patients oral Thromboembolism is a major cause of morbidity and pyridoxine rapidly reduces methionine and homocyste- the main cause of high premature mortality. Thromboses ine to near normal values. Folic acid should also be given. have been described in a wide variety of arteries and veins: Very large sustained doses (1000 mg/day or more) in cerebral, coronary, mesenteric, renal, and peripheral. adults can cause peripheral neuropathy which must be carefully followed. Those only partially or not respond- ing to pyridoxine require a strict low-protein diet supple- Diagnosis mented with a methionine-free amino acid supplement, Elevated plasma methionine values between 100 and minerals, and vitamins. Both folic acid (5–10 mg/day) 500 mmol/L (sometimes higher) are seen with plasma and betaine (up to 12 g/day) can further reduce plasma homocystine values of 50–200 mmol/L. A mixed disulfide homocysteine levels but may produce large elevations (half homocysteine, half cysteine) is always present at of plasma methionine. Treatment started early can pre- concentrations somewhat below homocystine. Diagnosis vent or reduce the clinical sequels and lowers the inci- requires the determination of fasting quantitative plasma dence of vascular events throughout life. AA, as well as plasma total homocysteine (tHcy). Total homocysteine measured by HPLC includes both homocys- METHYLENE TETRAHYDROFOLATE REDUCTASE teine moieties of homocystine, the homocysteine moiety DEFICIENCY of the mixed disulfide, and homocysteine bound to Clinical presentation plasma proteins. The urine gives a positive nitroprusside test (it is also positive in cystinuria and in the presence of Neurological features predominate with psychomotor sulfur-containing drugs). However, this test can be falsely retardation, seizures, abnormalities of gait, and psychiatric DEFECTS IN AMINO ACID CATABOLISM AND THE UREA CYCLE 1771 disturbance. The age of symptoms varies widely from OTHER DEFECTS OF SULFUR AMINO ACID METABOLISM infancy with a progressive encephalopathy with apnea, sei- Among several additional defects known, cystathioni- zures and microcephaly to adulthood with ataxia, motor nuria due to g-cystathionase deficiency is probably clin- abnormalities, psychiatric symptoms, subacute degenera- ically harmless. Cystathionine in excess of 1 g/day may tion of spinal cord, cerebrovascular events. Demyelination be excreted at clearance values close to the glomerular occurs and the changes may resemble the classic findings filtration rate. of subacute combined degeneration seen in cobalamin Methionine adenosyl transferase deficiency causes deficiency. The risk of vascular disease is high. raised plasma methionine levels (up to 1200 mmol/L; normal 15–30 mmol/L) and appears to be harmless in most patients. The enzyme defect is partial. Severe deficiency Diagnosis of MATI/III may be associated with demyelination and Plasma methionine concentrations are below normal neurological features. In such patients treatment with and plasma homocysteine concentrations in the range S-adenosyl-methionine (400 mg of the toluene sulfo- 20–200 mmol/L with an elevated excretion of 15– nate, twice daily) is an option. 600 mmol/day. As homocystine is easily missed on amino Glycine N-methyltransferase deficiency is very rare acid analysis, quantitative determination of tHcy by and was demonstrated in children with mild liver disease. HPLC is the most important clue to diagnosis. There is Biochemical findings included elevated plasma methio- no megaloblastic anemia. The enzyme can be assayed nine and S-adenosylmethionine levels. in liver, leukocytes, lymphocytes, or fibroblasts also Similarly rare appear to be patients affected with allowing prenatal diagnosis. S-adenosyl-homocysteine hydrolase and adenosine kinase deficiency. Pathology and clinical findings are significant in liver, muscle and the nervous system (Baric et al., 2004). Treatment and outcome Biochemical findings consist of elevated plasma methionine, S-adenosyl-homocysteine and S-adenosyl- Betaine in large doses (20–150 mg/kg/day) effectively methionine levels. tHcy and cystathionine may also be lowers plasma homocysteine and raises plasma methio- elevated. nine. Other treatments tried alone or in combination include folinic acid, hydroxocobalamin, pyridoxine, ABBREVIATIONS and methionine. Some have suggested a “cocktail” of Amino acid (AA) all these treatments. It is difficult to be sure of clinical Amino acid disorder (AAD) success. Glutaric aciduria type I (GA-I) Inborn error of metabolism (IEM) Maple syrup urine disease (MSUD) DEFICIENCIES OF METHIONINE SYNTHASE REDUCTASE Methylmalonyl-CoA mutase (MCM) (COBALAMIN E DEFECT) AND METHIONINE SYNTHASE Organic acid disorder (OAD) (COBALAMIN G DEFECT) Phenylalanine (Phe) Phenylketonuria (PKU) Clinical and biochemical findings of methionine Propionyl-CoA carboxylase (PCC) synthase reductase (cobalamin E defect) and methionine Tetrahydrobiopterin (BH4) synthase (cobalamin G defect) deficiencies are virtually Total homocysteine (tHcy) identical. Characteristic findings are developmental Urea cycle defect (UCD) delay and megaloblastic anemia, but the onset may be in later in childhood with dementia and spasticity. Reti- REFERENCES nal degeneration, cardiac defects, and hemolysis have been described. Aires CC, van Cruchten A, Ijlst L et al. (2010). New insights on Megaloblastic anemia occurs in almost all patients. the mechanisms of valproate-induced hyperammonemia: Biochemical findings include low plasma methionine inhibition of hepatic N-acetylglutamate synthase activity and raised tHcy. Methylmalonic acid should be mea- by valproyl-CoA. J Hepatol 55: 426–434. Baric I, Fumic K, Glenn B et al. (2004). sured in urine to exclude other cobalamin defects (see S-adenosylhomocysteine hydrolase deficiency in a human: methylmalonic acidurias). Molecular diagnosis is possi- a genetic disorder of methionine metabolism. Proc Natl ble for both conditions. Treatment involves large doses Acad Sci U S A 101: 4234–4239. of hydroxocobalamin with betaine and possibly folinic Barth PG, Scholte HR, Berden JA et al. (1983). An X-linked acid. Success of therapy and outcome is variable and mitochondrial disease affecting cardiac muscle, skeletal often unfavorable. muscle and neutrophil leucocytes. J Neurol Sci 62: 327–355. 1772 G.F. HOFFMANN AND S. KO¨ LKER Ben-Omran TI, Blaser S, Phillips H et al. (2006). Atypical phe- Mamourian AC, du Plessis A (1991). Urea cycle defect: a case notype in a boy with a maple syrup urine disease. J Inherit with MR and CT findings resembling infarct. Pediatr Metab Dis 29: 195–200. Radiol 21: 594–595. Bindu PS, Shehanaz KE, Christopher R et al. (2007). Mattson LR, Lindor NM, Goldman DH et al. (1995). Central Intermediate maple syrup urine disease: neuroimaging pontine myelinolysis as a complication of partial ornithine observations in 3 patients from South India. J Child carbamoyl transferase deficiency. Am J Med Genet 60: Neurol 22: 911–913. 210–213. Blau N, Duran M, Blaskovics ME et al. (Eds.), (2003). 2nd edn. Morton DH, Strauss KA, Robinson DL et al. (2002). Diagnosis In Physician0s Guide to the Laboratory Diagnosis of and treatment of maple syrup disease: a study of 36 Inherited Metabolic Disease. Springer, Heidelberg. patients. Pediatrics 109: 999–1008. Blau N, Hoffmann GF, Leonard J et al. (Eds.), (2005). Mudd SH, Skovby F, Levy HL et al. (1985). The natural his- Physician’s Guide to the Treatment and Follow-up of tory of homocystinuria due to cystathionine b-synthase Metabolic Diseases. Springer, Berlin. deficiency. Am J Hum Genet 37: 1–31. Campeau PM, Valayannopoulos V, Touati G et al. (2009). Oechsner M, Stehen C, Stu€renburg HJ et al. (1998). Management of West syndrome in a patient with methyl- Hyperammonaemic encephalopathy after initiation of malonic aciduria. J Child Neurol 27: 94–97. valproate therapy in unrecognised ornithine transcarbamy- Goodman SI, Markey SP, Moe PG et al. (1975). Glutaric acid- lase deficiency. J Neurol Neurosurg Psychiatry 64: uria: a “new” disorder of amino acid metabolism. Biochem 680–682. Med 12: 12–21. Perez-Cerda C, Garcı´a-Villoria J, Ofman R et al. (2005). 2- Gu€ngo€r S, Akinci A, Firat AK et al. (2008). Neuroimaging Methyl-3-hydroxybutyryl-CoA dehydrogenase (MHBD) findings in hyperargininemia. J Neuroimaging 18: deficiency: an X-linked inborn error of isoleucine metabo- 457–462. lism that may mimic a mitochondrial disease. Pediatr Res Harting I, Neumaier-Probst E, Seitz A et al. (2009). Dynamic 58: 488–491. changes of striatal and extrastriatal abnormalities in gluta- Prietsch V, Lindner M, Zschocke J et al. (2002). Emergency ric aciduria type I. Brain 132: 1764–1782. management of inherited metabolic disease. J Inherit Heringer J, Boy SPN, Ensenauer R et al. (2010). Use of guide- Metab Dis 25: 531–546. lines improves the neurological outcome in glutaric acid- Schulze A, Lindner M, Kohlmuller D et al. (2003). uria type I. Ann Neurol 68: 743–752. Expanded newborn screening for inborn errors of metabo- Hoffmann GF, Gibson KM, Trefz FK et al. (1994). lism by electrospray ionization-tandem mass spectrometry: Neurological manifestations of organic acid disorders. results, outcome, and implications. Pediatrics 111: Eur J Pediatr 153: S94–S100. 1399–1406. Hoffmann B, Helbling C, Schadewaldt P et al. (2006). Impact Struys EA, Salomons GS, Achouri Y et al. (2005). Mutations of longitudinal plasma leucine levels on the intellectual out- in the D-2-hydroxyglutarate dehydrogenase gene cause come in patients with classic MSUD. Pediatr Res 59: 17–20. D-2-hydroxyglutaric aciduria. Am J Hum Genet 76: Holmgren G, Brundin A, Gustavson KH et al. (1980). 358–360. Intermittent neurological symptoms in a girl with a maple Sutter R, Killer R, Bilz S et al. (2009). Cerebral edema and syrup urine disease (MSUD) variant. Neuropediatrics 11: intracranial hypertension in an adult with maple syrup urine 377–383. disease. Eur J Neurol 16: e45–e46. Ho€rster F, Baumgartner MR, Viardot C et al. (2007). Long- Takanashi JI, Barkovich AJ, Cheng SF et al. (2003). Brain MR term outcome in methylmalonic acidurias is influenced imaging in neonatal hyperammonemic encephalopathy by the underlying defect (muto, mut, cblA, cblB). resulting from proximal urea cycle disorders. AJNR Am Pediatr Res 62: 225–230. J Neuroradiol 24: 1184–1187. Koch R, Hanley W, Levy HL et al. (2003). The maternal phe- Tanaka K, Budd MA, Efron ML et al. (1966). Isovaleric acid- nylketonuria international study: 1984–2002. Pediatrics emia: a new genetic defect of leucine metabolism. Proc 112: 1523–1529. Natl Acad Sci U S A 56: 236–242. Ko€lker S, Garbade SF, Greenberg CR et al. (2006). Natural his- Wortmann S, Rodenburg RJ, Huizing M et al. (2006). tory, outcome, and treatment efficacy in children and adults Association of 3-methylglutaconic aciduria with with glutaryl-CoA dehydrogenase deficiency. Pediatr Res sensori-neural deafness, encephalpathy, and Leigh-like 59: 840–847. syndrome (MEGDEL association) in four patients with a Kornfeld M, Woodfin BM, Papile L et al. (1985). disorder of oxidative phosphorylation. Mol Genet Metab Neuropathology of ornithine carbamyl transferase defi- 88: 47–52. ciency. Acta Neuropathol (Berl) 65: 261–264. Wortmann SB, Rodenburg RJT, Jonckheere A et al. (2009). Kranendijk M, Struys EA, van Schaftingen E et al. (2010). Biochemical and genetic analysis of 3-methylglutaconic IDH2 mutations in patients with D-2-hydroxyglutaric acid- aciduria type IV: a diagnostic strategy. Brain 132: 136–146. uria. Science 330: 336. Wortmann SB, Kluijtmans LA, Rodenburg RJ et al. (2013). Lenke R, Levy HL (1980). Maternal phenylketonuria and 3-Methylglutaconic aciduria – lessons from 50 genes hyperphenylalaninemia: an international study of treated and 977 patients. J Inherit Metab Dis Jan 25 [epub ahead and untreated pregnancies. N Engl J Med 303: 1202–1208. of print]. DEFECTS IN AMINO ACID CATABOLISM AND THE UREA CYCLE 1773 Zinnanti WJ, Lazovic J, Griffin K et al. (2009). Dual mecha- Zschocke J, Ruiter JP, Brand J et al. (2000). Progressive infantile nism of brain injury and novel treatment strategy in maple neurodegeneration caused by 2-methyl-3-hydroxybutyryl- syrup urine disease. Brain 132: 903–918. CoA dehydrogenase deficiency: a novel inborn error of Zschocke J, Hoffmann GF (2011). Vademecum metabolicum. branched-chain fatty acid and isoleucine metabolism. Diagnosis and treatment of inborn errors of metabolism. Pediatr Res 48: 852–855. 3rd revised edn. Schattauer, Stuttgart.