0031-3998/07/6202-0225 PEDIATRIC RESEARCH Vol. 62, No. 2, 2007 Copyright © 2007 International Pediatric Research Foundation, Inc. Printed in U.S.A. Long-Term Outcome in Methylmalonic Acidurias Is Influenced (by the Underlying Defect (mut0, mut؊, cblA, cblB FRIEDERIKE HO¨ RSTER, MATTHIAS R. BAUMGARTNER, CAROLINE VIARDOT, TERTTU SUORMALA, PETER BURGARD, BRIAN FOWLER, GEORG F. HOFFMANN, SVEN F. GARBADE, STEFAN KO¨ LKER, AND E. REGULA BAUMGARTNER Department of General Pediatrics [F.H., P.B., G.F.H., S.F.G., S.K.], Division of Inborn Metabolic Diseases, University Children’s Hospital, D-69120 Heidelberg, Germany; Metabolic Unit [C.V., T.S., B.F. E.R.B.], University Children’s Hospital Basel, CH-4005 Basel, Switzerland; Division of Metabolism and Molecular Pediatrics [M.R.B.], University Children’s Hospital Zu¨rich, CH-8032 Zu¨rich, Switzerland ABSTRACT: Isolated methylmalonic acidurias comprise a hetero- mut0 defect with complete loss of MCM activity (1). Both geneous group of inborn errors of metabolism caused by defects of defects are caused by mutations in the MUT gene and there- 0 – methylmalonyl-CoA mutase (MCM) (mut , mut ) or deficient syn- fore belong to the same complementation group (MIM thesis of its cofactor 5=-deoxyadenosylcobalamin (AdoCbl) (cblA, #251000). Using somatic complementation analysis, defects cblB). The aim of this study was to compare the long-term outcome of AdoCbl synthesis can be subdivided into several groups, in patients from these four enzymatic subgroups. Eighty-three pa- tients with isolated methylmalonic acidurias (age 7–33 y) born three of which cause isolated methylmalonic acidurias, i.e. between 1971 and 1997 were enzymatically characterized and pro- cblA, cblB, and, less frequently, cblD defects (2). The cblA spectively followed to evaluate the long-term outcome (median defect (MIM #251100) is caused by mutations in the MMAA follow-up period, 18 y). Patients with mut0 (n ϭ 42), mutϪ (n ϭ 10), gene encoding a protein of unknown function (3), whereas the cblA (n ϭ 20), and cblB (n ϭ 11) defects were included into the cblB defect (MIM #251110) is caused by mutations in the study. Thirty patients (37%) died, and 26 patients survived with a MMAB gene encoding cobalamin adenosyltransferase (EC severe or moderate neurologic handicap (31%), whereas 27 patients 2.5.1.7) (4). (32%) remained neurologically uncompromised. Chronic renal fail- The clinical presentation of patients with isolated methyl- ure (CRF) was found most frequently in mut0 (61%) and cblB malonic acidurias is variable; however, neonatal manifestation patients (66%), and was predicted by the urinary excretion of meth- ylmalonic acid (MMA) before CRF. Overall, patients with mut0 and is usually associated with a severe disease course (5). Children cblB defects had an earlier onset of symptoms, a higher frequency of with neonatal onset frequently present with recurrent vomit- complications and deaths, and a more pronounced urinary excretion ing, muscular hypotonia, progressive alteration of conscious- of MMA than those with mutϪ and cblA defects. In addition, ness, and, finally, overwhelming illness that can progress to long-term outcome was dependent on the age cohort and cobalamin coma and death. Severe ketoacidosis and lactic acidosis, hy- responsiveness. (Pediatr Res 62: 225–230, 2007) perammonemia, hyperglycemia, hypoglycemia, neutropenia, anemia, or pancytopenia are frequently found. If untreated, solated methylmalonic acidurias (synonym: methylmalonic recurrent metabolic crises usually result in multiorgan failure or Iacidemias) comprise a group of autosomal recessively in- death. These metabolic crises are precipitated by conditions that herited disorders characterized by an accumulation of MMA. are likely to induce catabolic state (e.g. febrile illness). In other They are caused by deficient activity of the homodimeric patients with chronic progressive disease, psychomotor retarda- mitochondrial enzyme MCM (EC 5.4.99.2), which converts tion and failure to thrive are the leading symptoms (6,7). methylmalonyl-CoA to succinyl-CoA within the final cata- The first study on the natural history of methylmalonic bolic pathway of L-isoleucine, L-valine, L-methionine, and aciduria demonstrated differences in the disease course and L-threonine, odd-chain fatty acids, and the side chain of cho- outcome of patients with isolated methylmalonic acidurias, lesterol. Deficient activity of MCM is caused by defects in the with mut0 patients being most severely affected (8). However, MCM apoenzyme or deficient intracellular synthesis of its this has not been studied in further detail in later studies, cofactor AdoCbl. Two subgroups of MCM apoenzyme defi- which have classified patients according to the onset of clin- ciency have been delineated, i.e. mutϪ defect with residual ical symptoms and cobalamin responsiveness but not based on activity in the presence of high concentrations of AdoCbl and the underlying enzymatic defect (7,9,10). These studies have shown that the outcome was unfavorable in patients with early onset of symptoms and in those not responding to cobalamin. Received December 18, 2006; accepted March 23, 2007. Correspondence: Friederike Ho¨rster, M.D., Department of General Pediatrics, Divi- Although the overall survival has improved during the past sion of Inborn Metabolic Diseases, University Children’s Hospital, Im Neuenheimer two decades, the long-term outcome still remains disappoint- Feld 153, D-69120 Heidelberg, Germany; e-mail: [email protected] heidelberg.de This study was supported by Deutsche Forschungsgemeinschaft (DFG grant HO2501/ Abbreviations: AdoCbl, 5=-deoxyadenosylcobalamin; CRF, chronic renal 1-1 to F. Ho¨rster), the Swiss National Science Foundation (grant 3200-066878 to B. Fowler, T. Suormala, and M.R. Baumgartner) and the German Federal Ministry of failure; MCM, methylmalonyl-CoA mutase (EC 5.4.99.2); MMA, methyl- Education and Science (BMBF grant 01GM0305 to P. Burgard). malonic acid; OH-Cbl, hydroxycobalamin 225 226 HO¨ RSTER ET AL. ing (7,9). Neurologic outcome is often impaired by the man- crude cell or tissue homogenates (12), and incorporation of 14C-propionate ifestation of extrapyramidal movement disorder and develop- into acid-precipitable materials in intact fibroblasts that were grown in basal medium with or without added OH-Cbl (1 or 10 ␮g/mL) as previously mental delay (10). Furthermore, CRF is frequently found (11). described (13,14). Both holo-MCM (assay without AdoCbl) and total MCM The major aim of this study was to investigate the long-term (assay with 50–100 ␮M AdoCbl) activities were strongly decreased in mut0 Ϫ outcome in patients with isolated methylmalonic acidurias and and mut patients, whereas total MCM activity was normal in patients with 0 Ϫ deficient AdoCbl synthesis. Propionate incorporation was deficient in cells whether the underlying enzymatic defect (mut , mut , cblA, cultivated in basal medium, but cells showed a variable degree of response and cblB) plays an important role in the outcome. after administration of OH-Cbl, and, thus, in vitro OH-Cbl responsiveness was used to differentiate between mut0 and mutϪ patients. Cells of patients showing an at least 1.5-fold increase in propionate incorporation after admin- METHODS istration of OH-Cbl were classified as mutϪ, whereas those with less or no increase were classified as mut0. Patients with deficient AdoCbl synthesis Study population. Eighty-three patients (45 female, 38 male) with a were differentiated into cblA defect using somatic complementation analysis confirmed diagnosis of isolated methylmalonic acidurias from 37 European hospitals were included into this study. Patients were divided in three birth or cblB defect using complementation analysis or analysis of cobalamin cohorts, i.e. 1970–1979 (cohort I), 1980–1989 (cohort II), and 1990–1997 adenosyltransferase activity in fibroblast homogenates as described (2,15). In (cohort III), and were followed until July 2004 (Table 1). Preliminary data on two patients, the enzymatic classification was based on previous results of an the follow-up of some patients until 1992 were reported more than one decade affected sibling. ago but did not differentiate between cblA and cblB defects (11). There is no common consensus on the precise procedure for testing and The ethnic origin of the study patients was heterogeneous; however, most evaluating cobalamin responsiveness. In vivo cobalamin responsiveness was of them came from European countries, such as Germany (n ϭ 26), Turkey usually tested by measurement of urinary MMA after repetitive administra- (n ϭ 13), Switzerland (n ϭ 9), Belgium (n ϭ 8), Italy (n ϭ 8), Austria (n ϭ tion of OH-Cbl (1–10 mg i.m. or i.v.) during a clinical and metabolic stable 5), the Netherlands (n ϭ 4), France (n ϭ 2), Portugal (n ϭ 2), and Greece condition. In a minor subset of patients, a clinical trial of cobalamin was (n ϭ 1). Single patients from Tunisia, Libya, and Iran, or of unknown origin performed before stable conditions were achieved. However, most of these (n ϭ 2) were also included. The frequency of known consanguinity in these were retested later. families was high (30%; 22/73 families). Eighteen patients were siblings (nine Urinary excretion of MMA. Urinary concentration of MMA was quanti- families). fied by gas chromatography/mass spectrometry. To avoid a bias induced by All mut0 and cblB patients received a low-protein diet (with or without episodes of acute metabolic decompensation during which metabolic tests are administration of isoleucine-,