Potential for Misdiagnosis Due to Lack of Metabolic Derangement in Combined Methylmalonic Aciduria/Hyperhomocysteinemia (Cblc) in the Neonate

Original ...... Article Potential for Misdiagnosis Due to Lack of Metabolic Derangement in Combined Methylmalonic Aciduria/Hyperhomocysteinemia (cblC) in the Neonate

Cary O. Harding, MD methionine synthase activities results in combined methylmalonic De-Ann M. Pillers, MD, PhD aciduria/hyperhomocysteinemia (MMA/HCys) (Figure 1). This Robert D. Steiner, MD disorder is often associated with both neurologic and systemic Teodoro Bottiglieri, PhD abnormalities, but recent work suggests early-onset (first year of life) and late-onset subgroupings with somewhat different clinical David S. Rosenblatt, MD, PhD 2 Jason Debley, MD outcomes. In the early-onset group, the clinical course is characterized by progressive global neurologic disability K. Michael Gibson, PhD (hypotonia, seizures, developmental arrest) along with ophthalmologic and hematologic abnormalities. Childhood onset cblC defect is associated with milder hematologic abnormalities (often affecting only erythropoiesis), isolated extrapyramidal We report two infants with an inborn error of cobalamin (vitamin B12) metabolism whose clinical presentation in the first month of life strongly neurologic abnormalities and improved survival with only mild-to- suggested bacterial or viral sepsis. The absence of any acute metabolic moderate disability. Therapeutic intervention with derangement (acidosis, hyperammonemia, hypoglycemia, or ketosis) in hydroxycobalamin may improve biochemical abnormalities but association with clinical features suggesting sepsis (lethargy, obtundation) may not completely prevent permanent neurologic sequelae. could impede the correct diagnosis of cobalamin C (cblC) disorder. In In the current report, we present two infants whose clinical addition, this is the first documentation of cerebrospinal fluid presentation raised significant suspicion for acute onset neonatal hyperhomocysteinemia in cblC defect that was highly increased and is likely bacterial or viral sepsis. An inborn error of metabolism was not to be associated with neurotoxicity in cblC patients. initially regarded with high likelihood in the differential diagnosis, Journal of Perinatology (2003) 23, 384–386. doi:10.1038/sj.jp.7210955 most likely because of an absence of any acute metabolic derangement detectable by routine chemistry studies. In addition,

Cobalamin

Homocysteine Methylmalonyl-CoA INTRODUCTION CblC The cobalamin C (cblC) complementation group is the most defect Methionine Methylmalonyl- AdoCbl common inborn error of vitamin B12 metabolism, affecting both synthase MeCbl CoA mutase methylcobalamin and adenosylcobalamin biosynthesis.1 The resulting functional deﬁciency of methylmalonyl-CoA mutase and Methionine Succinyl-CoA

Figure 1. Homocysteine and methylmalonyl-CoA metabolism and the cblC defect in cobalamin metabolism. Cobalamin is essential for the Department of Pediatrics (C.O.H., De-A.M.P., R.D.S., K.M.G.), Oregon Health & Science University, Portland, OR, USA; Department of Molecular & Medical Genetics (C.O.H., De-A.M.P., R.D.S., metabolism of homocysteine and methylmalonyl-CoA. Methionine K.M.G.), Oregon Health & Science University, Portland, OR, USA; Institute of Metabolic Disease synthase catalyzes the conversion of homocysteine to methionine and (T.B.), Baylor University Medical Center, Dallas, TX, USA; Departments of Human Genetics, requires the cofactor methylcobalamin (MeCbl) as a methyl group Medicine, and Pediatrics (D.S.R.), McGill University, MUHC, Montreal, Quebec, Canada; and Department of Pediatrics (J.D.), Legacy Emanuel Children’s Hospital, Portland, OR, USA. donor. The metabolism of methylmalonyl-CoA to succinyl-CoA is accomplished by the enzyme methylmalonyl-CoA mutase and requires Presented in abstract form at the Annual Meeting, American College of Medical Genetics, March 8–12, 2000, Palm Springs, CA, USA. Published as: Gibson K, Steiner R, Grompe M, et al. the presence of adenosylcobalamin (AdoCbl). The cblC defect in Potential for clinical misdiagnosis of combined methylmalonic aciduria/homocysteinemia cobalamin metabolism prevents the synthesis of MeCbl and AdoCbl from (MMA/HCYS) due to absence of acute metabolic derangement. Genet Med 2000;2:62. dietary vitamin B12, causes functional deﬁciencies of methionine Address correspondence and reprint requests to Cary O. Harding, MD, FACMG, Oregon Health & synthase and methylmalonyl-CoA mutase, and results in combined Science University, 707 SW GAINES Road, CDRC-F, Portland, OR 97239-2998, USA. MMA/Hcys.

during biochemical genetic evaluation, we detected a massive neutropenia (Total WBC ¼ 5600/mm3, absolute neutrophil increase in HCys in cerebrospinal fluid (CSF) from one case. count ¼ 1000). Hgb and Hct were normal (13.1 g/dl and 37% This finding may provide insight into the underlying cause of respectively), while MCV ¼ 99 fl. Shortly after admission, recurrent neurologic deterioration in these and other cblC patients. generalized motor seizures developed in association with severe obtundation and extensor posturing. Both cranial CT and MRI MATERIALS AND METHODS scans were normal. Therapy with multiple anticonvulsants was required to prevent seizures during the first week of hospitalization. All procedures followed standard laboratory practice, employing Plasma amino-acid analysis revealed the presence of homocystine reagents of the highest available purity. Plasma amino acids and (54 mmol/l), and MMA was detected in urine by organic acid urine organic acids were quantified using ion-exchange analysis. chromatography and gas chromatography–mass spectrometry, Once the diagnosis of combined MMA/HCys was suspected, 3,4 respectively. HCys in plasma or CSF was quantified by reversed- treatment with intramuscular hydroxycobalamin (1 mg/day) was 5 phase HPLC with electrochemical detection. Determination of initiated in both infants. Oral l-carnitine (100 mg/kg/day) and 57 14 [ Co]-cyanocobalamin uptake and distribution, C-propionate betaine (1.5 g/kg/day) therapies were added later to assist with the 14 and C-methyltetrahydrofolate uptake (with and without disposal of MMA and HCys, respectively. On this regimen, seizures hydroxycobalamin), and cobalamin complementation studies were well-controlled, abnormal motor movements and muscle tone 2 in cultured fibroblasts were performed as described. Routine abnormalities improved, and full consciousness returned over a 2- 6 fibroblast culture followed established methods. week convalescence. Currently, both children are clinically stable, and have not suffered recurrent episodes of acute neurologic deterioration. Both children remain mildly diffusely hypotonic, and CASE REPORTS both motor and cognitive developmental parameters are moderately Patient 1, a 3-week-old male, presented to the emergency delayed. department with lethargy, decreased oral intake and dehydration. Parents were first cousins of Saudi Arabian descent. Initial physical examination was remarkable for lethargy, diffuse hypotonia, and RESULTS AND SIGNIFICANCE poor perfusion. Routine laboratory testing was significant only for Pertinent metabolite and enzyme findings are displayed in Table 1. leukopenia (total WBC ¼ 1500/mm3) and thrombocytopenia The data verify decreased uptake of [57Co]cyanocobalamin in (platelet count ¼ 29,000/mm3). Hgb, Hct, and MCV were all cultured fibroblasts derived from both patients, and concomitant normal (12.9 g/dl, 37.5%, and 97.8 fl, respectively) for age. inability to convert cyanocobalamin to functional species, Laboratory evaluation for bacterial sepsis was normal. The baby including adenosylcobalamin (the cofactor for methylmalonyl-CoA received empiric intravenous antibiotic therapy. Although perfusion mutase activity) or methylcobalamin (the cofactor for methionine improved, the lethargy did not respond to standard supportive care. synthase). Inability of fibroblasts to incorporate 14C-propionate and At 1 week after hospital admission and prior to diagnosis of 14C-methyltetrahydrofolate into acid-precipitable proteins is further combined MMA/HCys, several episodes of generalized motor evidence for these enzyme deficiencies. These data, in conjunction seizures in association with apnea occurred. EEG was mildly with complementation studies employing polyethylene glycol fusion abnormal with a discontinuous pattern and occasional intermittent of fibroblasts (not shown), indicate both patients belong to the cblC sharp transients seen bilaterally. Cranial CT scan was normal subgroup. without evidence of hydrocephalus or hemorrhage. Seizures During routine metabolic workup of patient 2, CSF amino acids responded to treatment with phenobarbital and phenytoin. were measured in a search for the underlying cause of her seizure Diagnostic evaluation for inborn errors of metabolism revealed the activity. To our knowledge, this is the first examination of CSF presence of homocystine in plasma (67 mmol/l) by amino-acid HCys levels in cblC deficiency. HCys concentration measured 35 mM analyzer and of MMA in the urine organic acid analysis. (normal <0.03 to 0.08 for age) in CSF, an approximate 400-fold Patient 2, a Hispanic female, presented at day 19 of life with increase over normal, and a 10-fold increase over that we have lethargy, diffuse hypotonia, dehydration, cough, and decreased oral seen in an infant with nutritional cobalamin deficiency (3.4 mM, intake. She had been seen twice in the emergency department and data not published). clinic, and had undergone a laboratory evaluation for bacterial Highly increased CSF HCys is likely to be associated with sepsis with empiric parenteral antibiotic therapy prior to her NICU neurotoxicity in cblC patients. Increased HCys will complex with admission. Physical examination revealed mild hepatomegaly free adenosine, thereby decreasing adenosine pools and impacting without splenomegaly, severe lethargy, diffuse hypotonia, but purine biosynthesis.7 Rates of transmethylation reactions (affecting mildly hyperactive symmetric deep tendon reflexes. She was afebrile DNA, RNA, and protein biosynthesis) are controlled by and normotensive. Laboratory evaluation demonstrated adenosylmethionine (AdoMet; methyl donor) and thrombocytopenia (platelet count ¼ 55,000/mm3) and mild adenosylhomocysteine (AdoHCys) concentrations. Moreover,

Journal of Perinatology 2003; 23:384–386 385 Harding et al. Potential Misdiagnosis of cblC Monocysteinemia

Table 1 Metabolic and Intact Fibroblast Analyses in Two Patients with cblC Methylmalonic Aciduria/Hyperhomocysteinemia

Subject Plasma total Urine Intact ﬁbroblasts Hcys* MMAw CNCbl CNCbl (%)y AdoCbl (%)y MeCbly 14C-propionate 14C-methyltetrahydrofolate uptake (%)z uptake (%)z uptake (%)z

Control <10 <2 100 11±7 15±4 58±7 100 100 (n=3) (n=3) (n=3) Patient 1 26–39 22–450 23 65 3 1 21 25 (n=8) (n=6) Patient 2 47–216 18–600 51 53 6 1 33 20 (n=4) (n=2)

*micromol/l by reverse-phase HPLC and electrochemical detection. wmmol/mol creatinine by isotope dilution gas chromatography–mass spectrometry. zUptake of [57Co]-cyanocobalamin. yThese values represent the distribution of [57Co]-labeled species in ﬁbroblasts, both as precursor cyanocobalamin (CNCbl) and products adenosylcobalamin (AdoCbl) and methylcobalamin (MeCbl). Remaining cobalamin products in patients with controls are either unidentiﬁed products or aqueous (nonprotein bound) cobalamin species. zIncorporation into acid-precipitable protein.

AdoHCys (the product of methyltransferase reactions) is a potent 2. Rosenblatt DS, Aspler AL, Shevell MI, Pletcher BA, Fenton WA, Seashore MR. inhibitor of methyltransferase reactions, with Ki values of 0.1 to Clinical heterogeneity and prognosis in combined methylmalonic aciduria and homocystinuria (cblC). J Inherit Metab Dis 1997;20:528–38. 10 mM (considerably lower than Km values for AdoMet). Thus, it is highly probable that increased CSF HCys will have a major impact 3. Slocum RH, Cummings JG. Amino acid analysis of physiological samples. on cerebral metabolism.8 In: Hommes FA, editor. Techniques in Diagnostic Human Biochemical Our results also suggest the prudence of pursuing a full Genetics. New York: Wiley-Liss; 1991. p. 87–126. 4. Sweetman L. Organic acid analysis. In: Hommes FA, editor. Techniques laboratory evaluation for inborn errors of metabolism in neonates in Diagnostic Human Biochemical Genetics. New York: Wiley-Liss; 1991. who present with the combination of deteriorating neurologic p. 143–76. status and systemic findings such as thrombocytopenia or 5. Rodriguez-Cortes H, Griener J, Hyland K, et al. Plasma homocysteine levels pancytopenia, even in the absence of more stereotypical laboratory and folate status in children with sickle cell anemia. J Pediatr Hematol signs of metabolic disease (metabolic acidosis, ketosis, Oncol 1993;21:219–23. hypoglycemia, or hyperammonemia). Inborn errors of metabolism 6. Gibson KM, Lee CF, Kamali V, et al. 3-Hydroxy-3-methylglutaryl-CoA lyase should be included in the differential diagnosis of any critically ill deficiency as detected by radiochemical assay in cell extracts by thin-layer infant but especially in those instances in which the laboratory chromatography, and identification of three new cases. Clin Chem evaluation for bacterial sepsis is negative. 1990;36:297–303. 7. Surtees R, Bowron A, Leonard J. Cerebrospinal fluid and plasma total homocysteine and related metabolites in children with cystathionine beta- synthase deficiency: the effect of treatment. Pediatr Res 1997;42:577–82. References 8. Hershfield M, Mitchell B. Immunodeficiency diseases caused by adenosine 1. Rosenblatt DS, Fenton WA. Inherited disorders of folate and cobalamin deaminase deficiency and purine nucleoside phosphorylase deficiency. transport and metabolism. In: Scriver C, Beaudet AL, Sly W, Valle D, editors. In: Scriver C, Beaudet AL, Sly W, Valle D, editors. The Metabolic and The Metabolic and Molecular Bases of Inherited Disease. 8th ed. New York: Molecular Bases of Inherited Disease. 8th ed. New York: McGraw-Hill; 2001. McGraw-Hill; 2001. p. 3897–933. p. 2585–626.

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