18 Disorders of

Anupam Chakrapani, Elisabeth Holme

18.1 Hereditary Tyrosinaemia Type I (Hepatorenal Tyrosinaemia) – 235 18.1.1 Clinical Presentation – 235 18.1.2 Metabolic Derangement – 235 18.1.3 Genetics – 236 18.1.4 Diagnostic Tests – 236 18.1.5 Treatment and Prognosis – 237

18.2 H ereditary Tyrosinaemia Type II (Oculocutaneous Tyrosinaemia, Richner-Hanhart Syndrome) – 238 18.2.1 Clinical Presentation – 238 18.2.2 Metabolic Derangement – 239 18.2.3 Genetics – 239 18.2.4 Diagnostic Tests – 239 18.2.5 Treatment and Prognosis – 239

18.3 Hereditary Tyrosinaemia Type III – 239 18.3.1 Clinical Presentation – 239 18.3.2 Metabolic Derangement – 239 18.3.3 Genetics – 240 18.3.4 Diagnostic Tests – 240 18.3.5 Treatment and Prognosis – 240

18.4 Transient Tyrosinaemia – 240

18.5 – 240 18.5.1 Clinical Presentation – 240 18.5.2 Metabolic Derangement – 241 18.5.3 Genetics – 241 18.5.4 Diagnostic Tests – 241 18.5.5 Treatment and Prognosis – 241

18.6 – 241 18.6.1 Clinical Presentation – 241 18.6.2 Metabolic Derangement – 241 18.6.3 Genetics – 241 18.6.4 Diagnostic Tests – 241 18.6.5 Treatment and Prognosis – 242

References – 242 234 Chapter 18 · Disorders of Tyrosine Metabolism

Tyrosine Metabolism Tyrosine is one of the least soluble amino acids, and other tissues by mitochondrial aspartate aminotrans- forms characteristic crystals upon precipitation. It de- ferase, but this plays only a minor role under rives from two sources, and hydroxylation of phe- normal conditions. The penultimate intermediates of nylalanine (. Fig. 18.1). Tyrosine is both glucogenic and tyrosine catabolism, maleylacetoacetate and fumaryl- ketogenic, since its catabolism, which proceeds pre- acetoacetate, can be reduced to succinylacetoacetate, dominantly in the cytosol, results in the formation followed by decarboxylation to succinylacetone. The of fumarate and acetoacetate. The first step of tyrosine latter is the most potent known inhibitor of the IV catabolism is conversion into 4-hydroxyphenylpyruvate biosynthetic enzyme, 5- dehydra- by cytosolic tyrosine aminotransferase. Transamination tase ( synthase, . Fig. 36.1). of tyrosine can also be accomplished in the liver and in

. Fig. 18.1. The tyrosine catabolic pathway. 1, Tyrosine amino- (deficient in tyrosinaemia type I); 5, aspartate aminotransferase; transferase (deficient in tyrosinaemia type II); 2, 4-hydroxy- 6, 5-aminolevulinic acid (5-ALA) dehydratase (porphobilinogen phenylpyruvate (deficient in tyrosinaemia type III, synthase). Enzyme defects are depicted by solid bars across the hawkinsinuria, site of inhibition by NTBC); 3, homogentisate arrows dioxygenase (deficient in alkaptonuria); 4, fumarylacetoacetase 235 18 18.1 · Hereditary Tyrosinaemia Type I (Hepatorenal Tyrosinaemia)

and in particular, is markedly abnormal com- Five inherited disorders of tyrosine metabolism are pared with other tests of liver function. is common known, depicted in Fig. 18.1. Hereditary tyrosinaemia and early hypophosphataemic bone disease may be present type I is characterised by progressive and secondary to renal tubular dysfunction. Acute renal tubular dysfunction with . Hereditary tyro- may be the initial presenting feature or may occur sub- sinaemia type II (Richner-Hanhart syndrome) presents sequently, precipitated by intercurrent illnesses as »hepatic with keratitis and blisterous lesions of the palms and crises« which are associated with and co- soles. Tyrosinaemia type III may be asymptomatic or agulopathy. Mortality is high in untreated patients [1]. associated with mental retardation. Hawkinsinuria Chronic liver disease leading to eventually may be asymptomatic or presents with occurs in most individuals with tyrosinaemia 1 – both as a and metabolic acidosis in infancy. In alkaptonuria symp- late complication in survivors of early-onset disease and as toms of usually appear in adulthood. a presenting feature of the later-onset forms. The cirrhosis Other inborn errors of tyrosine metabolism include is usually a mixed micromacronodular type with a variable oculocutaneous caused by a deficiency of degree of [2]. There is a high risk of carcinomatous -specific , converting tyrosine transformation within these nodules [1, 3]. Unfortunately, into DOPA-quinone; the deficiency of tyrosine hydroxy- the differences in size and fat content of the nodules make lase, the first enzyme in the synthesis of from it difficult to detect malignant changes (7 Sect. 18.1.5). tyrosine; and the deficiency of aromatic L- decarboxylase, which also affects metabo- Renal Disease lism. The latter two disorders are covered in 7 Chap. 29. A variable degree of renal dysfunction is detectable in most patients at presentation, ranging from mild tubular dys- function to renal failure. Proximal tubular disease is very common and can become acutely exacerbated during he- 18.1 Hereditary Tyrosinaemia Type I patic crises. Hypophosphataemic rickets is the most com- (Hepatorenal Tyrosinaemia) mon manifestation of proximal tubulopathy but generalised , renal tubular acidosis and glycosuria may 18.1.1 Clinical Presentation also be present [4]. Other less common renal manifestations include distal renal tubular disease, nephrocalcinosis and The clinical manifestations of tyrosinaemia type 1 are very reduced glomerular filtration rates. variable and an affected individual can present at any time from the neonatal period to adulthood. There is consider- Neurological Manifestations able variability of presentation even between members of Acute neurological crises can occur at any age. Typically, the the same family. crises follow a minor infection associated with anorexia and Clinically, tyrosinaemia type 1 may be classified based , and occur in two phases: an active period lasting on the age at onset of symptoms, which broadly correlates 1–7 days characterised by painful parasthesias and auto- with disease severity: an »acute« form that manifests before nomic signs that may progress to paralysis, followed by a 6 months of age with acute liver failure; a »subacute« form recovery phase over several days [5]. Complications include presenting between 6 months and 1 year of age with liver , extreme hyperextension, self-mutilation, respira- disease, failure to thrive, coagulopathy, , tory paralysis and . rickets and hypotonia; and a more »chronic« form that presents after the first year with chronic liver disease, renal Other Manifestations disease, rickets, and/or a -like Cardiomyopathy is a frequent incidental finding, but may syndrome. Treatment of tyrosinaemia type 1 with NTBC in be clinically significant [6]. Asymptomatic pancreatic cell the last decade (7 Sect. 18.1.5) has dramatically altered its hypertrophy may be detected at presentation, but hyper- natural history. insulinism and hypoglycaemia are rare [7].

Hepatic Disease The liver is the major organ affected in tyrosinaemia 1, and 18.1.2 Metabolic Derangement is a major cause of morbidity and mortality. Liver disease can manifest as acute hepatic failure, cirrhosis or hepato- Tyrosinaemia type 1 is caused by a deficiency of the enzyme cellular ; all three conditions may occur in the fumarylacetoacetate hydrolase (FAH), which is mainly same patient. The more severe forms of tyrosinaemia type 1 expressed in the liver and . The compounds imme- present in infancy with vomiting, diarrhoea, dia- diately upstream from the FAH reaction, maleylacetoacetate thesis, hepatomegaly, , hypoglycaemia, edema and (MAA) and fumarylacetoacetate (FAA), and their deriva- . Typically, liver synthetic function is most affected tives, succinylacetone (SA) and succinylacetoacetate (SAA) 236 Chapter 18 · Disorders of Tyrosine Metabolism

accumulate and have important pathogenic effects. The ef- various populations is unknown but it has been found in fects of FAA and MAA occur only in the cells of the organs many different ethnic groups. in which they are produced; these compounds are not found in body fluids of patients. On the other hand, their deri- vatives, SA and SAA are readily detectable in plasma and 18.1.4 Diagnostic Tests and have widespread effects. FAA, MAA and SA disrupt sulfhydryl metabolism by In symptomatic patients, biochemical tests of liver function forming adducts, thereby rendering cells sus- are usually abnormal. In particular, liver synthetic function ceptible to free radical damage [8, 9]. Disruption of sulf- is severely affected – coagulopathy and/or hypoalbumin- IV hydryl metabolism is also believed to cause secondary defi- emia are often present even if other tests of liver function ciency of two other hepatic , 4-hydroxyphenyl- are normal. In most acutely ill patients, D-fetoprotein levels pyruvate dioxygenase and adenosyltransferase, are greatly elevated. A Fanconi-type tubulopathy is often resulting in hypertyrosinemia and . present with aminoaciduria, phosphaturia and glycosuria, Additionally, FAA and MAA are alkylating agents and can and radiological evidence of rickets may be present. disrupt the metabolism of thiols, amines, DNA and other Elevated levels of succinylacetone in dried spots, important intracellular molecules. As a result of these plasma or urine are pathognomonic of tyrosinaemia type 1. widespread effects on intracellular metabolism, hepatic and Other metabolite abnormalities that are suggestive of the renal cells exposed to high levels of these compounds diagnosis include elevated plasma levels of tyrosine, phenyl- undergo either apoptotic cell death or a significant altera- alanine and methionine, reduced erythrocyte 5-aminole- tion of expression [10–12]. In patients who have devel- vulinate dehydratase activity and increased urinary 5-ALA oped cirrhosis, self-induced correction of the genetic defect excretion. and the enzyme abnormality occurs within some nodules Confirmation of the diagnosis requires either enzyme [13]. The clinical expression of hepatic disease may cor- assay or analysis. FAH assays may be performed relate inversely with the extent of mutation reversion in on liver biopsy, fibroblasts, lymphocytes or dried blood regenerating nodules [14]. The mechanisms that underlie spots [21–23]. Falsely elevated enzyme results may be ob- the development of within no- tained on liver biopsy if a reverted nodule is inadvertently dules are poorly understood. assayed. Enzyme assay results should therefore be inter- SA is a potent inhibitor of the enzyme 5-ALA dehydra- preted in the context of the patients’ clinical and biochemi- tase. 5-ALA, a neurotoxic compound, accumulates and is cal findings. excreted at high levels in patients with type 1 and is believed to cause the acute neurological crises seen Newborn Screening during decompensation [5]. SA is also known to disrupt Screening using tyrosine levels alone has been used in the renal tubular function, heme synthesis and immune func- past and has resulted in very high false positive and false tion [15–17]. negative rates [24]. More recently, methods based on the inhibitory effects of SA on porphobilinogen synthase, either alone or in combination with tyrosine levels have success- 18.1.3 Genetics fully reduced false-positive rates [25]. Molecular screening is possible in populations in which one or few Hereditary tyrosinaemia type I is inherited as an autosomal account for the majority of cases. recessive trait. The FAH gene has been localised to 15q 23–25 and more than 40 mutations have been reported [18]. Prenatal Diagnosis The most common mutation, IVS12+5(g-a), is found in If the causative mutations in a pregnancy at risk are known, about 25 % of the worldwide and is the predominant antenatal diagnosis is best performed by mutation analysis mutation in the French-Canadian population in which it ac- on chorionic villus sampling (CVS) or amniocytes. Alter- counts for >90 % of alleles. Another mutation, IVS6-1(g-t) native methods include FAH assay on CVS [26] or amnio- is found in around 60 % of alleles in patients from the cytes [27] and determination of SA levels in amniotic fluid Mediterranean area. Other FAH mutations are common [28]. However, FAH is expressed at low levels in chorionic within certain ethnic groups: W262X in Finns, D233V in tissue and interpretation of results may be difficult. Assay Turks, and Q64H in Pakistanis. There is no clear genotype- for elevated SA levels in amniotic fluid is very reliable and phenotype correlation [19]; spontaneous correction of can be performed as early as 12 weeks; however, occasional the mutation within regenerative nodules may influence the affected pregnancies have reported normal SA amniotic clinical phenotype [14]. A pseudodeficiency mutation, fluid levels [29]. When mutation analysis is not available for R341W, has been reported in healthy individuals who have prenatal diagnosis, we currently use a strategy combining in vitro FAH activity indistinguishable from patients with initial screening for the common pseudodeficiency muta- type 1 tyrosinaemia [20]. The frequency of this mutation in tion and FAH assay on CVS at 10 weeks; pregnancies that 237 18 18.1 · Hereditary Tyrosinaemia Type I (Hepatorenal Tyrosinaemia)

have low FAH activity on CVS subsequently undergo levels between 200 and 400 µmol/l using a combination of amniocentesis for amniotic fluid SA levels at 11–12 weeks a protein-restricted diet and and tyrosine for confirmation. free amino acid mixtures. A small proportion of acutely presenting patients (<10%) do not respond to NTBC treatment; in these pa- 18.1.5 Treatment and Prognosis tients, coagulopathy and jaundice progress and mortality is very high without urgent liver transplantation. Historically, tyrosinaemia type I was treated with a tyrosine Adverse events of NTBC therapy have been few. Tran- and phenylalanine restricted diet, with or without liver sient thrombocytopenia and neutropenia and transient transplantation. In 1992 a new drug, 2-(2-nitro-4-trifluoro- eye symptoms (burning//corneal erosion/cor- methylbenzoyl)-1,3-cyclohexanedione (NTBC), a potent neal clouding) have been reported in a small proportion of inhibitor of 4-hydroxyphenylpyruvate dioxygenase was patients [31]. The short- to medium-term prognosis in re- introduced (. Fig. 18.1, enzyme 2); it has revolutionised the sponders appears to be excellent. Hepatic and neurological treatment of type 1 tyrosinaemia and is now the mainstay decompensations are not known to occur on NTBC treat- of therapy [30]. ment, and clear deterioration of chronic liver disease is rare. Renal tubular dysfunction responds well to NTBC NTBC therapy, but long-standing renal disease may be irreversible. The rationale for the use of NTBC is to block tyrosine Neurological crises are rarely seen in patients treated with degradation at an early step so as to prevent the production NTBC. of toxic down-stream metabolites such as FAA, MAA and The risk of hepatocellular carcinoma appears to be SA; the levels of tyrosine, 4-hydroxyphenyl-pyruvate and much reduced in patients started early on NTBC treatment. -lactate concomitantly increase (. Fig. 18.1). The Gothen- In particular, the risk is very low if treatment is commenced berg multicentre study provides the major experience of before 6 months of age. In patients started on NTBC after NTBC treatment in tyrosinaemia type 1 [31]. Over 300 pa- 6 months of age, the risk of developing hepatocellular car- tients have been treated; of these, over 100 have been treat- cinoma increases with the age at which treatment is intro- ed for over 5 years. NTBC acts within hours of administra- duced; if NTBC is introduced after 2 years of age, the risk tion and has a long half-life of about 54 hours [32]. In pa- may not be much different from that in historical controls tients presenting acutely with hepatic decompensation, (. Table 18.1). It remains to be determined whether early rapid clinical improvement occurs in over 90% with nor- NTBC treatment can prevent liver cancer in the long term. malisation of prothrombin time within days of starting Studies on the animal mouse models suggest that late hepa- treatment. Other biochemical parameters of liver function tocellular carcinoma may occur even if NTBC treatment is may take longer to normalise: D-fetoprotein concentrations started at birth [10, 33]; careful long-term vigilance is there- may not normalise for up to several months after starting fore necessary in all patients. treatment. NTBC is recommended in an initial dose of The long-term neuropsychological outcome of NTBC- 1 mg/kg body weight per day [31]. Individual dose adjust- treated patients with tyrosinaemia type 1 is also unclear. ment is subsequently based on the biochemical response Many patients appear to have significant learning diffi- and the plasma NTBC concentration. Dietary restriction of culties; cognitive deficits affecting performance abilities phenylalanine and tyrosine is necessary to prevent the more than verbal abilities have been found in many patients known adverse effects of hypertyrosinaemia (see tyrosin- on psychological testing [34]. The etiology of these cogni- aemia type II). We currently aim to maintain tyrosine tive deficits is uncertain; whether they are related to NTBC

. Table 18.1. Risk of hepatocellular carcinoma (HCC) in tyrosinemia type 1

Number of patients Age (in years) at assessment Patients developing HCC (%)

Pre-NTBC Weinberg et al [3] 43 >2 16 (37%) Van Spronsen et al [1] 55 2–12 10 (18%)

Gothenberg NTBC study (2004) Treatment started at: < 6 months 180 2–13 1 (0.6 %) 6–12 months 61 2–12 1 (1.6%) 1–2 years 44 2–12 3 (7%) 2–7 years 65 2–19 14 (21%) > 7 years 26 7–31 9 (35%) 238 Chapter 18 · Disorders of Tyrosine Metabolism

treatment or high tyrosine levels or are a feature of tyrosine- below plasma tyrosine levels of 800 Pmol/l; however, lower mia 1 per se is unknown. levels (200–400 Pmol/l) are usually recommended due to Monitoring of patients on NTBC treatment should possible effects of hypertyrosinaemia on cognitive outcome. include regular blood tests for liver function, blood counts, Whether dietary treatment is used alone or in conjunction clotting studies, alpha fetoprotein, SA, plasma PBG syn- with NTBC, the principle is the same: natural protein intake thase activity, 5-ALA, NTBC levels and amino acid profile; is restricted to provide just enough phenylalanine plus tests of renal tubular and glomerular function; urinary SA tyrosine to keep plasma tyrosine levels <400 Pmol/l; the and 5-ALA; and hepatic imaging by ultrasound and CT/ rest of the normal daily protein requirement is given in the MRI. Blood levels of phenylalanine and tyrosine should be form of a phenylalanine- and tyrosine-free amino acid mix- IV frequently monitored and the diet supervised closely. ture. Some patients develop very low phenylalanine levels with this regimen and may require phenylalanine supple- Liver Transplantation ments [39]. Liver transplantation has been used for over two decades in treating type 1 tyrosinaemia, and appears to cure the Supportive Treatment hepatic and neurological manifestations [35, 36]. However, In the acutely ill patient supportive treatment is essential. even in optimal circumstances, it is associated with approx- Clotting factors, albumin, electrolytes and acid/base balance imately 5–10% mortality and necessitates lifelong immuno- should be closely monitored and corrected as necessary. suppressive therapy. Therefore, at present liver transplan- Tyrosine and phenylalanine intake should be kept to a mini- tation in type 1 tyrosinaemia is restricted to patients with mum during acute decompensation. Addition of vitamin D, acute liver failure who fail to respond to NTBC therapy, preferably 1,25 hydroxy vitamin D3 or an analogue, may and in patients with suspected hepatocellular carcinoma. be required to treat rickets. Infections should be treated Currently, there is no non-invasive way of reliably detecting aggressively. malignancy within hepatic nodules. Regular monitoring of plasma D-fetoprotein levels and of hepatic architecture on Pregnancy computerized tomography (CT) or magnetic resonance To date, no published data on pregnancies in patients on imaging (MRI) are essential; liver transplantation has to be NTBC treatment is available; one pregnancy in a liver- considered if these investigations suggest malignant trans- transplanted tyrosinaemia type 1 patient has had a favour- formation. Other situations in which liver transplantation able outcome [40]. may be considered relate to the irreversible manifestations of chronic liver disease, such as severe portal hypertension, growth failure and poor quality of life. 18.2 Hereditary Tyrosinaemia Type II The long-term impact of liver transplantation on renal (Oculocutaneous Tyrosinaemia, disease in tyrosinaemia type 1 is not fully known. Tubular Richner-Hanhart Syndrome) dysfunction improves in most patients, but does not always normalise. Glomerular function generally remains stable 18.2.1 Clinical Presentation but may be affected by nephrotoxic immunotherapy [34, 37]. Urinary SA excretion is much reduced after liver trans- The disorder is characterised by ocular lesions (about 75% plantation but does not normalise, presumably due to con- of the cases), skin lesions (80%), and neurological compli- tinued renal production [38]; whether this affects renal cations (60%), or any combination of these [41]. The dis- function long-term and predisposes to renal malignancy is order usually presents in infancy but may become manifest unknown. In patients with severe hepatic and renal disease, at any age. combined liver and kidney transplantation should be con- Eye symptoms are often the presenting problem and sidered. may start in the first months of life with photophobia, lacri- mation and intense burning pain [42]. The conjunctivae are Dietary Treatment inflamed and on slit-lamp examination herpetic-like cor- Before the advent of NTBC therapy, dietary protein restric- neal ulcerations are found. The lesions stain poorly with tion was the only available treatment for tyrosinaemia type fluorescein. In contrast with herpetic ulcers, which are 1 apart from liver transplantation. Dietary treatment was usually unilateral, the lesions in tyrosinaemia type II are helpful in relieving the acute symptoms and perhaps slow- bilateral. Neovascularisation may be prominent. Untreated, ing disease progression, but it did not prevent the acute and serious damage may occur with corneal scarring, visual im- chronic complications including hepatocellular carcinoma. pairment, and glaucoma. Currently, dietary therapy alone is not recommended, but Skin lesions specifically affect pressure areas and most is used in conjunction with NTBC therapy to prevent the commonly occur on the palms and soles [43, 44]. They complications related to hypertyrosinaemia. Ocular and begin as blisters or erosions with crusts and progress to dermatological complications are not believed to occur painful, nonpruritic hyperkeratotic plaques with an ery- 239 18 18.3 · Hereditary Tyrosinaemia Type III

thematous rim, typically ranging in diameter from 2 mm tyrosine and 4-tyramine are also increased. The diagnosis to 3 cm. can be confirmed by enzyme assay on liver biopsy or by The neurological complications are highly variable: mutation analysis. some patients are developmentally normal whilst others have variable degrees of developmental retardation. More severe neurological problems, including microcephaly, 18.2.5 Treatment and Prognosis seizures, self-mutilation and behavioural difficulties have also been described [45]. Treatment consists of a phenylalanine and tyrosine-restrict- It should be noted that the diagnosis of tyrosinaemia ed diet, and the skin and eye symptoms resolve within weeks type II has only been confirmed by enzymatic and/or mo- of treatment [44, 47]. Generally, skin and eye symptoms lecular genetic analysis in a minority of the described cases do not occur at tyrosine levels < 800 Pmol/l; however, as and it is possible that some of the patients actually have hypertyrosinaemia may be involved in the pathogenesis tyrosinaemia type III. of the neurodevelopmental symptoms, it may be beneficial to maintain much lower levels [48]. We currently aim to maintain plasma tyrosine levels of 200–400 Pmol/l using a 18.2.2 Metabolic Derangement combination of a protein-restricted diet and a phenylalanine and tyrosine free amino acid mixture. Growth and nutri- Tyrosinaemia type II is due to a defect of hepatic cytosolic tional status should be regularly monitored. tyrosine aminotransferase (. Fig. 18.1, enzyme 1). As a result of the metabolic block, tyrosine concentrations in Pregnancy serum and cerebrospinal fluid are markedly elevated. The There have been several reports of pregnancies in patients accompanying increased production of the phenolic acids with tyrosinaemia type II: some have suggested that un- 4-hydroxyphenyl-pyruvate, -lactate and -acetate (not shown treated hypertyrosinaemia may result in fetal neurological in . Fig. 18.1) may be a consequence of direct deamination of abnormalities such as microcephaly, seizures and mental tyrosine in the kidneys, or of tyrosine catabolism by mito- retardation [45, 49, 50]; however, other pregnancies have chondrial aminotransferase (. Fig. 18.1). Corneal damage is reported normal fetal outcome [45, 51]. In view of the un- thought to be related to crystallization of tyro sine in the certainty regarding possible fetal effects of maternal hyper- corneal epithelial cells, which results in disruption of cell tyrosinaemia, dietary control of maternal tyrosine levels function and induces an inflammatory response. Tyrosine during pregnancy is recommended [50]. crystals have not been observed in the skin lesions. It has been suggested that excessive intracellular tyro sine enhances cross-links between aggregated tonofilaments and modu- 18.3 Hereditary Tyrosinaemia Type III lates the number and stability of microtubules [46]. As the skin lesions occur on pressure areas, it is likely that mechan- 18.3.1 Clinical Presentation ical factors also play a role. The etiology of the neurological manifestations is unknown, but it is believed that hyper- Only 13 cases of tyrosinaemia type III have been described tyrosinaemia may have a role in pathogenesis. and the full clinical spectrum of this disorder is unknown [52]. Many of the patients have presented with neurological symptoms including intellectual impairment, ataxia, in- 18.2.3 Genetics creased tendon reflexes, tremors, microcephaly and sei- zures; some have been detected by the finding of a high Tyrosinaemia type II is inherited as an autosomal recessive tyrosine concentration on neonatal screening. The most trait. The gene is located at 16q22.1-q22.3. Twelve different common long-term complication has been intellectual im- mutations have so far been reported in the tyrosine amino- pairment, found in 75% of the reported cases. None of the transferase gene [35]. Prenatal diagnosis has not been re- described cases have developed signs of liver disease in the ported. long-term. Eye and skin lesions have not been reported so far, but as oculocutaneous symptoms are known to occur in association with hypertyrosinaemia it is reasonable to be 18.2.4 Diagnostic Tests aware of this possibility.

Plasma tyrosine concentrations are usually above 1200 Pmol/ l. When the tyrosinaemia is less pronounced a diagnosis of 18.3.2 Metabolic Derangement tyrosinaemia type III should be considered (7 Sect. 18.3). Urinary excretion of the phenolic acids 4-hydroxyphenyl- Tyrosinaemia type III is due to deficiency of 4-hydroxy- pyruvate, -lactate, -acetate is highly elevated and N-acetyl- phenylpyruvate dioxygenase (HPD) (. Fig. 18.1, enzyme 2), 240 Chapter 18 · Disorders of Tyrosine Metabolism

which is expressed in liver and kidney. As a result of the infants than full term newborns. The level of protein intake enzyme block there is an increased plasma tyrosine concen- is an important etiological factor: the incidence of transient tration and increased excretion in urine of 4-hydroxy- tyrosinaemia has fallen dramatically in the last 4 decades, phenyl-pyruvate and its derivatives 4-hydroxyphenyl- concomitant with a reduction in the protein content of new- lactate and 4-hydroxyphenyl-acetate. The aetiology of the born formula milks. Transient tyrosinaemia is clinically neurological symptoms is not known, but they may be re- asymptomatic. Tyrosine levels are extremely variable, and lated to hypertyrosinaemia as in tyrosinaemia types 1 and 2. can exceed 2000 Pmol/l. Hypertyrosinaemia usually resolves spontaneously by 4–6 weeks; protein restriction to less than 2 g/kg/day with or without supplementation IV 18.3.3 Genetics results in more rapid resolution in most cases. Although the disorder is generally considered benign, some reports have Tyrosinaemia type III follows autosomal recessive inherit- suggested that it may be associated with mild intellectual ance. The HPD gene has been localised to 12q24-qter and deficits in the long term [54, 55]. However, large systematic 5 mutations associated with tyrosinaemia III have been de- studies have not been performed. scribed [35]. There is no apparent genotype-phenotype cor- relation; some patients with enzymatically defined HPD deficiency do not have identifiable mutations in the HPD 18.5 Alkaptonuria gene [52, 53]. 18.5.1 Clinical Presentation

18.3.4 Diagnostic Tests Some cases of alkaptonuria are diagnosed in infancy due to darkening of urine when exposed to air. However, clinical Elevated plasma tyrosine levels of 300–1300 Pmol/l have symptoms first appear in adulthood. The most prominent been found in the described cases at diagnosis. Elevated symptoms relate to joint and connective tissue involvement; urinary excretion of 4-hydroxyphenyl-pyruvate, -lactate significant cardiac disease and urolithiasis may be detected and -acetate usually accompanies the increased plasma in the later years [56]. tyrosine concentration. Diagnosis can be confirmed by The pattern of joint involvement resembles osteoarthri- enzyme assay in liver or kidney biopsy specimens or by mu- tis. In general, joint disease tends to be worse in males than tation analysis. in females. The presenting symptom is usually either limita- tion of movement of a large joint or low back pain starting in the 3rd or 4th decade. Spinal involvement is progressive 18.3.5 Treatment and Prognosis and may result in kyphosis, limited spine movements and height reduction. On X-ray examination, narrowing of At present, tyrosinemia type III appears to be associated with the disk spaces, calcification and vertebral fusion may be intellectual impairment in some cases, but not in others. It evident. In addition to the spine, the large weight-bearing is unknown whether lowering plasma tyrosine levels will joints such as the hips, knees and ankles are usually in- alter the natural history. Amongst the patients described, the volved. Radiological abnormalities may range from mild cases detected by neonatal screening and treated early appear narrowing of the joint space to destruction and calcifica- to have fewer neurological abnormalities than those diag- tion. Synovitis, ligament tears and joint effusions have also nosed on the basis of neurological symptoms [52]; whether been described. The small joints of the hands and feet tend this is due to ascertainment bias or due to therapeutic inter- to be spared. Muscle and tendon involvement is common: vention is unclear. Until there is a greater understanding thickened Achilles tendons may be palpable, and tendons of the etiology of the neurological complications of tyro- and muscles may be susceptible to rupture with trivial sinaemia type III, it is reasonable to treat patients with a trauma. The clinical course is characterised by episodes of low-phenylalanine and tyrosine diet. We currently recom- acute exacerbation and progressive joint disability; joint mend maintaining plasma tyrosine levels between 200 and replacement for chronic pain may be required. Physical 400 Pmol/l. No pregnancy data is available to date. disability increases with age and may become very severe by the 6th decade. A greyish discoloration (ochre on microscopic exami- 18.4 Transient Tyrosinaemia nation, thus the name ) of the and the ear usually appears after 30 years of age. Subse quently, Transient tyrosinaemia is one of the most common amino dark coloration of the skin particularly over the nose, cheeks acid disorders, and is believed to be caused by late fetal and in the axillary and pubic areas may become evident. maturation of 4-hydroxyphenylpyruvate dioxygenase Cardiac involvement probably occurs in most patients (. Fig. 18.1, enzyme 2). It is more common in premature eventually; aortic or calcification or regurgi- 241 18 18.6 · Hawkinsinuria

tation and coronary artery calcification is evident on CT homogentisate excretion; the concomitant hypertyrosin- scan and echocardiography in about 50% of patients by the aemia requires dietary adjustment to prevent ocular, cuta- 6th decade [56]. A high frequency of renal and prostatic neous and neurological complications [56]. None of these stones has also been reported. therapies have been subjected to long-term clinical trials, and currently, no treatment can be recommended as being effective in preventing the late effects of alkaptonuria. 18.5.2 Metabolic Derangement To date, there is no published data on pregnancies in patients with alkaptonuria. Alkaptonuria was the first disease to be interpreted as an inborn error of metabolism in 1902 by Garrod [57]. It is caused by a defect of the enzyme homogentisate dioxy- 18.6 Hawkinsinuria genase (. Fig. 18.1, enzyme 3), which is expressed mainly in the liver and the kidneys. There is accumulation of homo- 18.6.1 Clinical Presentation gentisate and its oxidised derivative benzoquinone acetic acid, the putative toxic metabolite and immediate precursor This rare condition, which has only been described in four to the dark pigment, which gets deposited in various tissues. families [65–67], is characterised by failure to thrive and The relationship between the pigment deposits and the metabolic acidosis in infancy. After the first year of life the systemic manifestations is not known. It has been proposed condition appears to be asymptomatic. Early weaning from that the pigment deposit may act as a chemical irritant [58]; breastfeeding seems to precipitate the disease; the condition alternatively, inhibition of some of the enzymes involved in may be asymptomatic in breastfed infants. connective tissue metabolism by homogentisate or benzo- quinone acetic acid may have a role in pathogenesis [59]. 18.6.2 Metabolic Derangement

18.5.3 Genetics The abnormal metabolites produced in hawkinsinuria (hawkinsin (2-cysteinyl-1,4-dihydroxycyclohexenylacetate) Alkaptonuria is an autosomal recessive disorder. The gene and 4-hydroxycycloxylacetate) are thought to derive from for homogentisate oxidase has been mapped to chromo- an incomplete conversion of 4-hydroxyphenylpyruvate to some 3q2, and over 40 mutations have been identified homogentisate caused by a defect 4-hydroxyphenylpyruvate [35]. The estimated incidence is between 1:250 000 and dioxygenase (. Fig. 18.1, enzyme 2). Hawkinsin is thought 1:1 000 000 live births. to be the product of a reaction of an epoxide intermediate with glutathione, which may be depleted. The metabolic acidosis is believed to be due to 5-oxoproline accumulation 18.5.4 Diagnostic Tests secondary to glutathione depletion.

Alkalinisation of the urine from alkaptonuric patients results in immediate dark brown coloration of the urine. 18.6.3 Genetics Excessive urinary homogentisate also results in a positive test for reducing substances. Gas chromatography – mass Unlike most other inborn errors of metabolism, hawkinsin- spectrometry (GC-MS) based organic acid screening me- uria shows autosomal dominant inheritance. The molecular thods can specifically identify and quantify homogentisic basis of the condition is unknown. It is believed that a spe- acid. Homogentisate may also be quantified by HPLC [60] cific mutation or a limited number of mutations in the and by specific enzymatic methods [61]. 4-hydroxyphenylpyruvate dioxygenase gene can partially disrupt enzyme activity and lead to the production of hawkinsin and 4-hydroxycyclohexylacetate. Neither the 18.5.5 Treatment and Prognosis enzymatic defect nor the molecular genetics have been studied in detail. A number of different approaches have been used to attempt treatment. Dietary restriction of phenylalanine and tyrosine intake reduces homogentisate excretion, but compliance is a 18.6.4 Diagnostic Tests major problem as the diagnosis is usually made in adults [62]. Ascorbic acid prevents the binding of 14C-homo- Identification of urinary hawkinsin or 4-hydroxycyclo- gentisic acid to connective tissue in rats [63] and reduces hexylacetate by GC-MS is diagnostic [67]. Hawkinsin is the excretion of benzoquinone acetic acid in urine [64]. a ninhydrin-positive compound, which appears between Administration of the drug NTBC also reduces urinary urea and threonine in ion-exchange chromatography of 242 Chapter 18 · Disorders of Tyrosine Metabolism

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