Begoña Merinero

Natural history, outcome, and treatment efficacy in children and adults with glutaryl-CoA dehydrogenase deficiency.

Glutaryl-CoA dehydrogenase (GCDH) deficiency is a rare inborn disorder of l-lysine, l-hydroxylysine, and l-tryptophan metabolism complicated by striatal damage during acute encephalopathic crises. Three decades after its description, the natural history and how to treat this disorder are still incompletely understood. To study which variables influenced the outcome, we conducted an international cross-sectional study in 35 metabolic centers. Our main outcome measures were onset and neurologic sequelae of acute encephalopathic crises. A total of 279 patients (160 male, 119 female) were included who were diagnosed clinically after clinical presentation (n = 218) or presymptomatically by neonatal screening (n = 23), high-risk screening (n = 24), or macrocephaly (n = 14). Most symptomatic patients (n = 185) had encephalopathic crises, characteristically resulting in bilateral striatal damage and dystonia, secondary complications, and reduced life expectancy. First crises usually occurred during infancy (95% by age 2 y); the oldest age at which a repeat crisis was reported was 70 mo. In a few patients, neurologic disease developed without a reported crisis. Differences in the diagnostic criteria and therapeutic protocols for patients with GCDH deficiency resulted in a huge variability in the outcome worldwide. Recursive partitioning demonstrated that timely diagnosis in neurologically asymptomatic patients followed by treatment with l-carnitine and a lysine-restricted diet was the best predictor of good outcome, whereas treatment efficacy was low in patients diagnosed after the onset of neurologic disease. Notably, the biochemical phenotype did not predict the clinical phenotype. Our study proves GCDH deficiency to be a treatable disorder and a good candidate for neonatal screening.

Proposed guidelines for the diagnosis and management of methylmalonic and propionic acidemia

Methylmalonic and propionic acidemia (MMA/PA) are inborn errors of metabolism characterized by accumulation of propionic acid and/or methylmalonic acid due to deficiency of methylmalonyl-CoA mutase (MUT) or propionyl-CoA carboxylase (PCC). MMA has an estimated incidence of ~ 1: 50,000 and PA of ~ 1:100-000 -150,000. Patients present either shortly after birth with acute deterioration, metabolic acidosis and hyperammonemia or later at any age with a more heterogeneous clinical picture, leading to early death or to severe neurological handicap in many survivors. Mental outcome tends to be worse in PA and late complications include chronic kidney disease almost exclusively in MMA and cardiomyopathy mainly in PA. Except for vitamin B12 responsive forms of MMA the outcome remains poor despite the existence of apparently effective therapy with a low protein diet and carnitine. This may be related to under recognition and delayed diagnosis due to nonspecific clinical presentation and insufficient awareness of health care professionals because of disease rarity.These guidelines aim to provide a trans-European consensus to guide practitioners, set standards of care and to help to raise awareness. To achieve these goals, the guidelines were developed using the SIGN methodology by having professionals on MMA/PA across twelve European countries and the U.S. gather all the existing evidence, score it according to the SIGN evidence level system and make a series of conclusive statements supported by an associated level of evidence. Although the degree of evidence rarely exceeds level C (evidence from non-analytical studies like case reports and series), the guideline should provide a firm and critical basis to guide practice on both acute and chronic presentations, and to address diagnosis, management, monitoring, outcomes, and psychosocial and ethical issues. Furthermore, these guidelines highlight gaps in knowledge that must be filled by future research. We consider that these guidelines will help to harmonize practice, set common standards and spread good practices, with a positive impact on the outcomes of MMA/PA patients.

Glutaryl-CoA Dehydrogenase Deficiency in Spain: Evidence of Two Groups of Patients, Genetically, and Biochemically Distinct

Glutaryl-CoA dehydrogenase (GCDH) deficiency causes glutaric aciduria type I (GA I), an inborn error of metabolism that is characterized clinically by dystonia and dyskinesia and pathologically by neural degeneration of the caudate and putamen. Studies of metabolite excretion allowed us to categorize 43 GA I Spanish patients into two groups: group 1 (26 patients), those presenting with high excretion of both glutarate and 3-hydroxyglutarate, and group 2 (17 patients) , those who might not be detected by routine urine organic acid analysis because glutarate might be normal and 3-hydroxyglutarate only slightly higher than controls. Single-strand conformation polymorphism (SSCP) screening and sequence analysis of the 11 exons and the corresponding intron boundaries of the GCDH gene allowed us to identify 13 novel and 10 previously described mutations. The most frequent mutations in group 1 were A293T and R402W with an allele frequency of 30% and 28%, respectively. These two mutations were also found in group 2, but always in heterozygosity, in particular in combination with mutations V400M or R227P. Interestingly, mutations V400M and R227P were only found in group 2, and at least one of these mutations was found in 11 of 15 unrelated alleles, accounting together for 53% of the mutant alleles in group 2. Therefore, it seems clear that two genetically and biochemically distinct groups of patients exist. The severity of the clinical phenotype seems to be closely linked to the development of encephalopathic crises rather than to residual enzyme activity or genotype. Comparison of GCDH protein with other acyl-CoA dehydrogenases (whose x-ray crystal structure has been determined) reveals that most of the mutations identified in GCDH protein seem to affect folding and tetramerization, as has been described for a number of mutations affecting mitochondrial β-oxidation acyl-CoA dehydrogenases.

Correlation of genotype and phenotype in glutaryl-CoA dehydrogenase deficiency

Summary: We have investigated the correlation between genotype and phenotype in a large number of patients with glutaric aciduria type I (GA I). The deficiency of glutaryl-CoA dehydrogenase has been confirmed in the Rigshospitalets laboratory in 215 patients since 1975. Most of the patients were of European ancestry. Complete absence of enzyme activity was found in more than half of the patients, while 34% of patients had a residual activity up to 5% and a few patients had a residual activity of 5–15%. In four exceptional cases, a very high residual activity of up to 30% was found. Enzyme studies are thus a reliable method for confirming the diagnosis of GA I, although it may be difficult to distinguish exceptional mild cases from heterozygous carriers for GA I. Three of the patients with very high residual activity are compound heterozygous for the missense mutations R227P and V400M, both of which are associated with residual enzyme activity of 8–10% in homozygous patients. Patients with a mild mutation on at least one chromosome frequently show unusual biochemical findings such as low or normal urinary excretion of glutaric acid and mild or only slightly increased excretion of 3-hydroxyglutaric acid. In contrast, patients with severe mutations such as R402W or A293T on both alleles have no residual activity and show the typical urinary metabolite pattern. Clinical data were available for a subgroup of 79 patients. No correlation with the biochemical phenotype or the genotype could be established.

2-Methyl-3-hydroxybutyryl-CoA dehydrogenase (MHBD) deficiency : An X-linked inborn error of isoleucine metabolism that may mimic a mitochondrial disease

We describe three patients, from two Spanish families, with 2-methyl-3-hydroxybutyryl-CoA dehydrogenase (MHBD) deficiency, a recently described X-linked neurodegenerative inborn error of isoleucine metabolism. Two of them are males with severe lactic acidosis suggestive of a mitochondrial encephalopathy, and the third is a female who was less severely affected, suggesting skewed X-inactivation. Molecular studies revealed a new missense mutation, 740A→G, in one family and a previously described mutation, 388C→T, in the other, causing the amino acid substitutions N247S and R130C, respectively. Both male patients died, one of them despite treatment with an isoleucine-restricted diet, but the disease has remained stable in the female patient after 1 y of treatment.

An unusual late-onset case of propionic acidaemia: biochemical investigations, neuroradiological findings and mutation analysis

Abstract We report a 5-year-old boy with propionic acidaemia who developed a rapidly fatal necrosis of the basal ganglia after an episode of clinical deterioration. Neither metabolic acidosis nor hyperammonaemia were present. Organic acid analysis in both urine and CSF showed increased levels of methylcitric and 3-hydroxypropionic acids. Propionic acidaemia was confirmed by demonstrating a propionyl-CoA carboxylase deficiency (11% of control value) in skin fibroblasts. DNA analysis revealed that the patient was a compound heterozygote for two mutations in the PCCB gene. nConclusion Propionic acidaemia can present as a sudden and fatal neurological disease and not only as an organic aciduria with severe biochemical dis-turbances and progressive neurological deterioration.

Newborn screening for homocystinurias and methylation disorders: systematic review and proposed guidelines

Newborn screening (NBS) is justified if early intervention is effective in a disorder generally not detected early in life on a clinical basis, and if sensitive and specific biochemical markers exist. Experience with NBS for homocystinurias and methylation disorders is limited. However, there is robust evidence for the success of early treatment with diet, betaine and/or pyridoxine for CBS deficiency and good evidence for the success of early betaine treatment in severe MTHFR deficiency. These conditions can be screened in dried blood spots by determining methionine (Met), methionine-to-phenylanine (Met/Phe) ratio, and total homocysteine (tHcy) as a second tier marker. Therefore, we recommend NBS for cystathionine beta-synthase and severe MTHFR deficiency. Weaker evidence is available for the disorders of intracellular cobalamin metabolism. Early treatment is clearly of advantage for patients with the late-onset cblC defect. In the early-onset type, survival and non-neurological symptoms improve but the effect on neurocognitive development is uncertain. The cblC defect can be screened by measuring propionylcarnitine, propionylcarnitine-to-acetylcarnitine ratio combined with the second tier markers methylmalonic acid and tHcy. For the cblE and cblG defects, evidence for the benefit of early treatment is weaker; and data on performance of Met, Met/Phe and tHcy even more limited. Individuals homozygous or compound heterozygous for MAT1A mutations may benefit from detection by NBS using Met, which on the other hand also detects asymptomatic heterozygotes. Clinical and laboratory data is insufficient to develop any recommendation on NBS for the cblD, cblF, cblJ defects, glycineN-methyltransferase-, S-adenosylhomocysteinehydrolase- and adenosine kinase deficiency.

A new patient with dicarboxylic aciduria suggestive of medium-chain acyl-CoA dehydrogenase deficiency presenting as Reye's syndrome

A new patient with medium-chain dicarboxylic aciduria and suberyl glycinuria during an attack of acute illness is reported. When, inadvertently he was given medium-chain triglycerides for 2 days, the excretion of abnormal metabolites of medium-chain fatty acids increased and hepatomegaly became more pronounced. During remission a low excretion of the metabolites were observed. After 16 h of fasting hypoglycaemia was accompanied by an increase of urinary dicarboxylic acids and ψ-hydroxyacids similar to that found on admission. Interestingly this urinary organic acid pattern persisted 8 h after intravenous administration of glucose. In a blood sample obtained after 16 h of fasting there was hypoketonaemia and increased levels of total free fatty acids, octanoic, decanoic andcis-4-decenoic acids. These biochemical data suggest the existence of a deficiency at the level of medium-chain acyl-CoA dehydrogenase.

Study of inborn errors of metabolism in urine from patients with unexplained mental retardation

Mental retardation (MR) is a common disorder frequently of unknown origin. Because there are few studies regarding MR and inborn errors of metabolism (IEM), we aimed to identify patients with IEM from a cohort of 944 patients with unexplained MR. Biochemical examinations such as determination of creatine (Cr) metabolites, acylcarnitines, purine, and pyrimidines in urine were applied. We found seven patients with IEM [three with cerebral Cr deficiency syndromes (CCDS)], one with adenylosuccinate lyase (ADSL) deficiency, and three, born before the neonatal metabolic screening program in Catalonia, with phenylketonuria (PKU). All told, they represent 0.8% of the whole cohort. All of them had additional symptoms such as epilepsy, movement disorders, autism, and other psychiatric disturbances. In conclusion, in patients with MR, it is essential to perform a thorough appraisal of the associated signs and symptoms, and in most disorders, it is necessary to apply specific analyses. In some cases, it is important to achieve an early diagnosis and therapy, which may reduce the morbimortality, and to offer genetic counselling.

Clinical, biochemical, and molecular studies in pyridoxine-dependent epilepsy. Antisense therapy as possible new therapeutic option

Pyridoxine‐dependent epilepsy seizure (PDE; OMIM 266100) is a disorder associated with severe seizures that can be controlled pharmacologically with pyridoxine. In the majority of patients with PDE, the disorder is caused by the deficient activity of the enzyme α‐aminoadipic semialdehyde dehydrogenase (antiquitin protein), which is encoded by the ALDH7A1 gene. The aim of this work was the clinical, biochemical, and genetic analysis of 12 unrelated patients, mostly from Spain, in an attempt to provide further valuable data regarding the wide clinical, biochemical, and genetic spectrum of the disease.