[New insights in inborn errors of metabolism are leading to new paradigms in child neurology]. / Nuevos conocimientos sobre errores congenitos del metabolismo estan dando lugar a nuevos paradigmas en neuropediatria.

In the last recent years, the -omics era has already transformed child neurology. Next generation sequencing (NGS) has identified many novel disease causing genes and phenotypes. While genetics is of great importance as a diagnostic tool, it is less helpful when it comes to a comprehensive understanding of mechanisms of brain dysfunction. Child neurologists are at high risk of being lost in genomics if they do not face the necessity of a new approach in their clinical practice. The large amount of data provided by NGS is just one more element in a complex puzzle. Different levels of complexity should be integrated in the much-needed novel child neurology paradigm. Classically, the descriptions of neurological diseases have relied on neuroanatomy and neurophysiology. However, metabolism, which strongly orchestrates the regulation of neuronal functions, has been mostly neglected in the study of brain disorders. Paradoxically, inborn errors of metabolism (IEM) have moved in the opposite direction. With more than 1100 IEM, almost 80% of which exhibit neurological symptoms, they have evolved from being initially considered as mere anecdotes to be a fundamental requisite in neuropediatric educational programs. Additionally, new complex molecule defects are leading to integrate classic metabolism and cell biology into the specific compartmentalized structure of the nervous system («cellular neurometabolism¼). This article is a brief summary of the updated IEM classification combined with major neurological presentations in a tentative towards a pathophysiology based clinical practice in child neurology. In particular we emphasize a clinical approach focused in a continuum/spectrum of symptoms.

TITLE: Nuevos conocimientos sobre errores congenitos del metabolismo estan dando lugar a nuevos paradigmas en neuropediatria.En los ultimos anos, la era -omica ya ha transformado la neuropediatria. La secuenciacion de alto rendimiento --next generation sequencing (NGS)-- ha permitido identificar numerosos genes y fenotipos nuevos que provocan enfermedades. Aunque la genetica tiene indudablemente una gran importancia como herramienta diagnostica, no es de tanta utilidad cuando se trata de obtener una comprension mas amplia de los mecanismos involucrados en la disfuncion cerebral. Los neuropediatras corren el riesgo de perderse en la genomica si no asumen la necesidad de un nuevo enfoque en su practica clinica. La gran cantidad de datos que arroja la NGS es simplemente un elemento mas en un complejo rompecabezas. Se deberian integrar distintos niveles de complejidad en el nuevo paradigma de la neuropediatria que tanto se echa en falta. Tradicionalmente, las descripciones de las enfermedades neurologicas se han basado en la neuroanatomia y la neurofisiologia. Sin embargo, el metabolismo, que tiene un papel crucial en la regulacion de las funciones neuronales, se ha obviado en la mayoria de estudios sobre los trastornos cerebrales. Paradojicamente, los errores congenitos del metabolismo (ECM) han tomado la direccion contraria. Con un total de mas de 1.100 ECM, casi el 80% de los cuales manifiestan sintomas neurologicos, han pasado de considerarse inicialmente como anecdoticos a constituir un elemento fundamental en cualquier programa de educacion neuropediatrica. Ademas, los nuevos defectos hallados en las moleculas complejas estan promoviendo la integracion del metabolismo y la biologia celular clasicos en la estructura compartimentada especifica del sistema nervioso («neurometabolismo celular¼). Este articulo constituye un breve resumen de la clasificacion de los ECM actualizada en combinacion con las principales presentaciones neurologicas en un intento de lograr una practica clinica neuropediatrica basada en la fisiopatologia. De manera particular, hacemos hincapie en un enfoque clinico centrado en un amplo continuo/espectro de sintomas.

Disorders of phospholipids, sphingolipids and fatty acids biosynthesis: toward a new category of inherited metabolic diseases.

We wish to delineate a novel, and rapidly expanding, group of inborn errors of metabolism with neurological/muscular presentations: the defects in phospholipids, sphingolipids and long chain fatty acids biosynthesis. At least 14 disorders have been described so far. Clinical presentations are diverse but can be divided into (1) diseases of the central nervous system; (2) peripheral neuropathies; and (3) muscular/cardiac presentations. (1) Leukodystrophy and/or iron deposits in basal ganglia is a common feature of phospholipase A2 deficiency, fatty acid hydroxylase deficiency, and pantothenate kinase-associated neurodegeneration. Infantile epilepsy has been reported in GM3 synthetase deficiency. Spastic quadriplegia with ichthyosis and intellectual disability are the presenting signs of the elongase 4 deficiency and the Sjogren-Larsson syndrome caused by fatty aldehyde dehydrogenase deficiency. Spastic paraplegia and muscle wasting are also seen in patients with mutations in the neuropathy target esterase gene. (2) Peripheral neuropathy is a prominent feature in PHARC syndrome due to α/ß-hydrolase 12 deficiency, and in hereditary sensory autonomic neuropathy type I due to serine palmitoyl-CoA transferase deficiency. (3) Muscular/cardiac presentations include recurrent myoglobinuria in phosphatidate phosphatase 1 (Lipin1) deficiency; cardiomyopathy and multivisceral involvement in Barth syndrome secondary to tafazzin mutations; congenital muscular dystrophy due to choline kinase deficiency, Sengers syndrome due to acylglycerol kinase deficiency and Chanarin Dorfman syndrome due to α/ß- hydrolase 5 deficiency. These synthesis defects of complex lipid molecules stand at the frontier between classical inborn errors of metabolism and other genetic diseases involving the metabolism of structural proteins.

Molecular characterization of 82 patients with pyruvate dehydrogenase complex deficiency. Structural implications of novel amino acid substitutions in E1 protein.

BACKGROUND: Pyruvate dehydrogenase complex (PDHc) deficiencies are an important cause of primary lactic acidosis. Most cases result from mutations in the X-linked gene for the pyruvate dehydrogenase E1α subunit (PDHA1) while a few cases result from mutations in genes for E1ß (PDHB), E2 (DLAT), E3 (DLD) and E3BP (PDHX) subunits or PDH-phosphatase (PDP1). AIM: To report molecular characterization of 82 PDHc-deficient patients and analyze structural effects of novel missense mutations in PDHA1. METHODS: PDHA1 variations were investigated first, by exon sequencing using a long range PCR product, gene dosage assay and cDNA analysis. Mutation scanning in PDHX, PDHB, DLAT and DLD cDNAs was further performed in unsolved cases. Novel missense mutations in PDHA1 were located on the tridimensional model of human E1 protein to predict their possible functional consequences. RESULTS: PDHA1 mutations were found in 30 girls and 35 boys. Three large rearrangements, including two contiguous gene deletion syndrome were identified. Novel missense, frameshift and splicing mutations were also delineated and a nonsense mutation in a mosaic male. Mutations p.Glu75Ala, p.Arg88Ser, p.Arg119Trp, p.Gly144Asp, p.Pro217Arg, p.Arg235Gly, p.Tyr243Cys, p.Tyr243Ser, p.Arg245Gly, p.Pro250Leu, p.Gly278Arg, p.Met282Val, p.Gly298Glu in PDHA1 were predicted to impair active site channel conformation or subunit interactions. Six out of the seven patients with PDHB mutations displayed the recurrent p.Met101Val mutation; 9 patients harbored PDHX mutations and one patient DLD mutations. CONCLUSION: We provide an efficient stepwise strategy for mutation screening in PDHc genes and expand the growing list of PDHA1 mutations analyzed at the structural level.

Comprehensive cDNA study and quantitative analysis of mutant HADHA and HADHB transcripts in a French cohort of 52 patients with mitochondrial trifunctional protein deficiency.

BACKGROUND: Deficiency of mitochondrial trifunctional protein (MTP) is caused by mutations in the HADHA and HADHB genes, which have been mostly delineated at the genomic DNA level and have not been always elucidated. AIM: To identify mutations in a French cohort of 52 MTP deficient patients and the susceptibility of mutations generating premature termination codons (PTCs) to the nonsense mRNA mediated decay (NMD). METHODS: Mutation screening in fibroblasts was performed at the cDNA level and real-time RT-PCR was used to compare the levels of the different PTC-bearing mRNAs before and after a treatment of fibroblasts by emetine, a translation inhibitor. RESULTS: A mutation detection rate of 100% was achieved. A total of 22 novel mutations were identified, including a large-sized genomic deletion in HADHB gene. A high proportion of all identified mutations were non-sense, frameshift and splicing mutations, generating (PTCs), distributed essentially on HADHA coding regions. We could demonstrate that the majority of mutations resulting in PTCs conform to the established rules governing the susceptibility to NMD. CONCLUSION: Our results emphasize the value of cDNA analysis in the characterization of HADHA and HADHB mutations and further strengthen the model of haploinsufficiency as a major pathomechanism in MTP defects.

Secondary creatine deficiency in ornithine delta-aminotransferase deficiency.

AIMS: Ornithine delta-aminotransferase (OAT) deficiency causes gyrate atrophy (GA) of the retina, as a consequence of high plasma ornithine concentrations. Because creatine synthesis requires the conversion of arginine and glycine into ornithine and guanidinoacetate, high ornithine concentration inhibits this reaction thus causing secondary creatine deficiency. The aim of this study was to evaluate the neuropsychological features and creatine metabolism in patients with GA. METHODS: The study involved 7 GA patients, aged from 11 to 27 years who underwent neuropsychological evaluation and cerebral proton magnetic resonance spectroscopy (MRS). RESULTS: Neurocognitive impairment was found in 5/7 patients, including mental retardation (3/7), school failure (1/7), major visuospatial dyspraxia (1/7), aggressive behavior (3/7) and epilepsy (2/7). Two patients had normal neuropsychological evaluation. Cerebral proton magnetic resonance spectroscopy revealed a profound creatine deficiency in all patients. MRS data were confirmed by decreased levels of creatine and/or guanidinoacetate in plasma and urine in all patients. CONCLUSIONS: In our group of patients with GA, we found a high prevalence of neurological impairment, not reported so far, and possibly related to secondary creatine deficiency and hyperornithinemia. We propose to treat mentally retarded GA patients with high doses of creatine, as it may normalize brain creatine levels and help to reduce ornithine levels.

[Inborn errors of metabolism in adults]. / Les maladies héréditaires du métabolisme à l'âge adulte.

We present a simplified classification of treatable inborn errors of metabolism (IEM) in three groups with a special focus on those disorders observed at adult age. Group 1 includes inborn errors (IE) of intermediary metabolism which give rise to an acute or chronic intoxication. It encompasses aminoacidopathies, organic acidurias (OA), urea cycle disorders (UCD), sugar intolerances, metal storage disorders and porphyrias. Clinical expression can be acute, systemic or involves a specific organ, it can strike in the neonatal period or later and intermittently from infancy to late adulthood. Most of these disorders are treatable and require the emergency removal of the toxin by special diets, extracorporeal procedures, cleansing drugs or vitamins. Group 2 includes IE of intermediary metabolism which affect the cytoplasmic and mitochondrial energetic processes. Cytoplasmic defects encompass those affecting glycolysis, glycogenosis, gluconeogenesis, creatine and pentose phosphate pathways; the latter are untreatable. Mitochondrial defects include respiratory chain disorders, Krebs cycle and pyruvate oxidation defects, mostly untreatable, and disorders of fatty acid oxidation and ketone bodies that are treatable. Group 3 involves cellular organelles and include lysosomal, peroxisomal, glycosylation, and cholesterol synthesis defects. Among these, some lysosomal disorders can be efficiently treated by enzyme replacement or substrate reduction therapies. Physicians can be faced with the possibility of a treatable IE in emergency, either in the neonatal period or late in infancy to adulthood, or as chronic and progressive symptoms, general (failure to thrive), neurological, or specific for various organs or systems. These symptoms and the simplified classification of IEM are summarized in seven tables.

Movement disorders and inborn errors of metabolism in adults: a diagnostic approach.

Inborn errors of metabolism (IEMs) may present in adolescence or adulthood with various movement disorders including parkinsonism, dystonia, chorea, tics or myoclonus. Main diseases causing movement disorders are metal-storage diseases, neurotransmitter synthesis defects, energy metabolism disorders and lysosomal storage diseases. IEMs should not be missed as many are treatable. Here we briefly review IEMs causing movement disorders in adolescence and adults and propose a simple diagnostic approach to guide metabolic investigations based on the clinical course of symptoms, the type of abnormal movements, and brain MRI abnormalities.

Leukoencephalopathies associated with inborn errors of metabolism in adults.

The discovery of a leukoencephalopathy is a frequent situation in neurological practice and the diagnostic approach is often difficult given the numerous possible aetiologies, which include multiple acquired causes and genetic diseases including inborn errors of metabolism (IEMs). It is now clear that IEMs can have their clinical onset from early infancy until late adulthood. These diseases are particularly important to recognize because specific treatments often exist. In this review, illustrated by personal observations, we give an overview of late-onset leukoencephalopathies caused by IEMs.

Recessive hereditary methaemoglobinaemia, type II: delineation of the clinical spectrum.

Type II recessive hereditary methaemoglobinaemia (RHM) is a rare disease due to generalized NADH-cytochrome b5 reductase (cytb5r) deficiency. It results in mild cyanosis and severe neurological impairment. The clinical features and long-term outcome are poorly documented, and there are no systematic reviews. We examined six cases of type II RHM, four of which were new, together with 45 previously published cases, in order to establish the range of phenotypic expression. The clinical picture was very similar in most cases, with severe encephalopathy, microcephaly, generalized dystonia, movement disorders and mild cyanosis. The neurological prognosis was poor; in particular, none of the patients walked or spoke. In addition, the possibility of an atypical and milder phenotype was considered. We concluded that children with unexplained severe encephalopathy associated with generalized dystonia should be examined for cyanosis and have a methaemoglobinaemia assay performed. The diagnosis can be confirmed by very low cytb5r activity in both red and white blood cells. Here we report three novel mutations in the NADH-cytochrome b5 reductase gene. Prenatal diagnosis of this extremely severe disease should be proposed to affected families.

[Treatable hereditary neuro-metabolic diseases]. / Les maladies métaboliques héréditaires traitables en neurologie.

Hereditary metabolic diseases may appear during adolescence or young adulthood, revealed by an apparently unexplained neurological or psychiatric disorder. Certain metabolic diseases respond to specific treatments and should be identified early, particularly in emergency situations where rapid introduction of a treatment can avoid fatal outcome or irreversible neurological damage. The main diseases leading to an acute neurological syndrome in the adult are urea cycle disorders, homocysteine metabolisms disorders and porphyria. More rarely, Wilson's disease, aminoacid diseases, organic aciduria, or pyruvate dehydrogenase deficiency, beta-oxidation disordes or biotin metabolism may be involved. Most emergency situations can be screen correctly with simple tests (serum ammonia, homocysteine, lactate, urinary prophyrines, acylcarnitine pattern, amino acid and organic acid chromatography). For chronic situations, the main treatable diseases are Wilson's disease, homocysteine, cerebrotendinous xanthomatosis, Refsum's disease, vitamin E deficiency, Gaucher's disease, Fabry's disease, and neurotransmitter metabolism disorders. We present treatable metabolic disorders as a function of the different clinical situations observed in adults.

Hereditary spastic paraparesis in adults associated with inborn errors of metabolism: a diagnostic approach.

Spastic paraparesis is a general term describing progressive stiffness and weakness in the lower limbs caused by pyramidal tract lesions. This clinical situation is frequently encountered in adult neurology. The diagnostic survey is usually limited to searching for acquired causes (spinal cord compression, inflammatory, metabolic, infectious diseases) and the so-called 'hereditary spastic paraparesis'. Although poorly recognized by neurologists, spastic paraparesis is also one of the multiple presentations of inborn errors of metabolism (IEMs) in children and adults. Pyramidal signs are usually included in a diffuse neurological or systemic clinical picture; however, in some cases spastic paraparesis remains the only symptom for years. Since these metabolic causes are often treatable, it is essential to include them in the general diagnostic approach to spastic paraparesis. Here we review IEMs causing paraparesis in adults.

Epilepsy and inborn errors of metabolism in adults: a diagnostic approach.

Inborn errors of metabolism (IEMs) represent poorly known causes of epilepsy in adulthood. Although rare, these are important to recognize for several reasons: some IEMs respond to specific treatments, some antiepileptic drugs interfering with metabolic pathways may worsen the clinical condition, and specific genetic counselling can be provided. We review IEMs potentially revealed by epilepsy that can be encountered in an adult neurology department. We distinguished progressive myoclonic epilepsies (observed in some lysosomal storage diseases, respiratory chain disorders and Lafora disease), from other forms of epilepsies (observed in disorders of intermediary metabolism, including porphyrias, creatine metabolism defects, glucose transporter (GLUT-1) deficiency, Wilson disease or succinic semialdehyde dehydrogenase deficiency). We propose a diagnostic approach and point out clinical, radiological and electrophysiological features that suggest an IEM in an epileptic patient.

Psychiatric manifestations revealing inborn errors of metabolism in adolescents and adults.

Inborn errors of metabolism (IEMs) may present in adolescence or adulthood as a psychiatric disorder. In some instances, an IEM is suspected because of informative family history or because psychiatric symptoms form part of a more diffuse clinical picture with systemic, cognitive or motor neurological signs. However, in some cases, psychiatric signs may be apparently isolated. We propose a schematic classification of IEMs into three groups according to the type of psychiatric signs at onset. Group 1 represents emergencies, in which disorders can present with acute and recurrent attacks of confusion, sometimes misdiagnosed as acute psychosis. Diseases in this group include urea cycle defects, homocysteine remethylation defects and porphyrias. Group 2 includes diseases with chronic psychiatric symptoms arising in adolescence or adulthood. Catatonia, visual hallucinations, and aggravation with treatments are often observed. This group includes homocystinurias, Wilson disease, adrenoleukodystrophy and some lysosomal disorders. Group 3 is characterized by mild mental retardation and late-onset behavioural or personality changes. This includes homocystinurias, cerebrotendinous xanthomatosis, nonketotic hyperglycinaemia, monoamine oxidase A deficiency, succinic semialdehyde dehydrogenase deficiency, creatine transporter deficiency, and alpha and beta mannosidosis. Because specific treatments should be more effective at the 'psychiatric stage' before the occurrence of irreversible neurological lesions, clinicians should be aware of atypical psychiatric symptoms or subtle organic signs that are suggestive of an IEM. Here we present an overview of IEMs potentially revealed by psychiatric problems in adolescence or adulthood and provide a diagnostic strategy to guide metabolic investigations.

Dihydropteridine reductase deficiency: levodopa's long-term effectiveness without dyskinesia.

We report an adult patient lacking endogenous synthesis of monoamines (dopamine, serotonin, and catecholamines) due to a severe dihydropteridine reductase (DHPR) deficiency. With levodopa and 5-hydroxytryptophan (5HTP) supplementation, the patient exhibited moderate mental retardation, acute episodes of parkinsonism, and episodes of depression. Despite the use of levodopa from age 3 months, he exhibited no dyskinesia or dopaminergic cell loss as suggested by normal PET imaging of the dopamine transporter.

Methylmalonic and propionic acidurias: management without or with a few supplements of specific amino acid mixture.

In a series of 137 patients with methylmalonic acidaemia (MMA) and propionic acidaemia (PA) diagnosed since the early 1970s, we report in more detail 81 patients (51 MMA and 30 PA) diagnosed between 1988 and 2005. In this series, 14% of patients died at initial access revealing the disease before or despite treatment, 18% died later, and the remainder (68%) are still alive. All patients were treated with the same protocol of enteral feeds with a low-protein diet adjusted to individual tolerance, carnitine, antibiotics, and only occasional use of an amino acid (AA) mixture. There was intensive follow-up and monitoring using measurements of urinary urea. Thirty-nine patients with severe forms, followed for more than 3 years, are analysed in particular detail. Of the 17 PA patients, 6 had moderate disability (all neonatal-onset forms), whereas 11 were normal or slightly delayed in their mental development. Four presented with cardiomyopathy, of whom 2 died. Of the 22 MMA patients, 13 presented in the neonatal period, of whom 3 died later, 2 are in renal failure and only 5 are still alive and have a normal or slightly delayed mental development. In the 9 patients with late-onset forms, there were no deaths and all patients but one have normal mental development. Among the 39 patients, only 40% were given an AA supplement at 3 years, and 50% between 6 and 11 years. The actual intake of natural protein was 0.92, 0.78 and 0.77 g/kg per day at 3, 6 and 11 years, respectively, in patients without AA supplementation, whereas it was 0.75, 0.74 and 0.54 g/kg per day in the group who received small quantities of AA (0.4-0.6 g/kg per day). In both groups, feeding disorders were frequent: 55% at 3 years, 35% at 6 years and 12% at 11 years. Many patients were given a food supplement by tube overnight or were even exclusively tube fed: 60% at 3 years, 48% at 6 years and still 27% at 11 years. Growth velocity was near the normal values. Plasma valine and isoleucine were low to very low, as were leucine and phenylalanine but to a lesser extent. Albumin, vitamins, trace elements and markers of bone metabolism were within the normal values. IGF1, 24-hour urine calcium and body mass density were low. Body composition showed a normal to low lean mass and a normal to high fat mass.

Clinical approach to treatable inborn metabolic diseases: an introduction.

In view of the major improvements in treatment, it has become increasingly important that in order for first-line physicians not to miss a treatable disorder they should be able initiate a simple method of clinical screening, particularly in the emergency room. We present a simplified classification of treatable inborn errors of metabolism in three groups. Group 1 includes inborn errors of intermediary metabolism that give rise to an acute or chronic intoxication. It encompasses aminoacidopathies, organic acidurias, urea cycle disorders, sugar intolerances, metal disorders and porphyrias. Clinical expression can be acute or systemic or can involve a specific organ, and can strike in the neonatal period or later and intermittently from infancy to late adulthood. Most of these disorders are treatable and require the emergency removal of the toxin by special diets, extracorporeal procedures, cleansing drugs or vitamins. Group 2 includes inborn errors of intermediary metabolism that affect the cytoplasmic and mitochondrial energetic processes. Cytoplasmic defects encompass those affecting glycolysis, glycogenosis, gluconeogenesis, hyperinsulinisms, and creatine and pentose phosphate pathways; the latter are untreatable. Mitochondrial defects include respiratory chain disorders, and Krebs cycle and pyruvate oxidation defects, mostly untreatable, and disorders of fatty acid oxidation and ketone bodies that are treatable. Group 3 involves cellular organelles and includes lysosomal, peroxisomal, glycosylation, and cholesterol synthesis defects. Among these, some lysosomal disorders can be efficiently treated by enzyme replacement or substrate reduction therapies. Physicians can be faced with the possibility of a treatable inborn error in an emergency, either in the neonatal period or late in infancy to adulthood, or as chronic and progressive symptoms--general (failure to thrive), neurological, or specific for various organs or systems. These symptoms are summarized in four tables. In addition, an extensive list of medications used in the treatment of inborn errors is presented.

Breast feeding in IMD.

Breast feeding has proven benefits for many infants with inherited metabolic disorders (IMDs) but, with the exception of phenylketonuria, there are few reports in other conditions. A questionnaire, completed by dietitians and clinicians from 27 IMD centres from 15 countries (caring for a total of over 8000 patients with IMDs on diet) identified breast feeding experience in IMD. Successful, demand breast feeding (in combination with an infant amino acid formula free of precursor amino acids) was reported in 17 infants with MSUD, 14 with tyrosinaemia type I, and 5 with homocystinuria. Eighty-nine per cent were still breast fed at 16 weeks. Fewer infants with organic acidaemias were demand breast fed (7 with propionic acidaemia; 6 with methylmalonic acidaemia and 13 with isovaleric acidaemia) (usually preceded by complementary feeds of a protein-free infant formula or infant amino acid formula free of precursor amino acids). Only 12 infants with urea cycle disorders were given demand breast feeds, but this was unsuccessful beyond 8 days in CPS deficiency. Further work is needed in developing guidelines for feeding and for clinical and biochemical monitoring for breast-fed infants with IMDs.

[Status of lysosomal diseases amongst metabolic diseases]. / Place des maladies lysosomales dans les maladies métaboliques.

Lysosomal diseases belong to the group of diseases which disturb the synthesis, catabolism or processing of complex molecules. These are the most common metabolic diseases, as they account for about one-third of all known metabolic diseases. They can be expressed as early as the intra-uterine stage of life, or appear after birth at any age, including during adulthood. They develop gradually, evolve independently of any intercurrent catabolic event and are independent of diet. Although they have long been associated with an inevitably fatal outcome, several can now be treated effectively, either by enzyme replacement therapy which increases catabolism of the overloaded substance thanks to an input of the deficient enzyme, or by drugs which reduce the synthesis of the overloaded substance.

Long-term follow-up of neonatal mitochondrial cytopathies: a study of 57 patients.

OBJECTIVES: We sought to determine the long-term clinical and biochemical outcome of newborns with mitochondrial cytopathies (MCs) and to identify possible prognostic factors that may modify the course of these diseases. MATERIAL AND METHODS: Fifty-seven newborns with MCs were identified in a retrospective review (1983-2002). We defined 2 different outcome categories: clinical (neurologic, hepatic, myopathic, and multiorganic) and biochemical (lactate level normalization or initially normal remaining unchanged, decreased but not normalized, and persistently high). We used 2 different statistical approaches: (1) survival studies depending on the initial symptoms and lactate and enzymatic deficiencies using the Kaplan-Meier method; and (2) the same variables compared with different survival age groups and clinical and biochemical outcome categories using the chi2 test. RESULTS: Thirty-three patients died (57.8%), 12 remain alive (21%), and 12 were lost in the follow-up; 6 of them are currently older than 4 years. Most of the patients manifested multiorganic disease (64.8%) and high lactate level (77.1%) over time. Children surviving to 2.5 to 3 years of age were more likely to survive for a long period of time. Initial neurologic and hepatic presentation increased the risk to develop neurologic disease and severe persistent hyperlactacidemia, respectively. Initial severe hyperlactacidemia and combined enzyme deficiencies were significant risk factors for higher mortality and multiorganic disorders. Two patients with exclusively myopathic outcome are alive and cognitively normal at 12 years of life. CONCLUSIONS: Children with neonatal-onset MCs have very high mortality and poor prospects. However, some with life-threatening presentations may gradually improve, giving rise to less severe diseases. Those with exclusively myopathic symptoms have a better prognosis.