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 ␤-oxidation acyl-CoA dehydrogenases.

This article describes a hitherto unreported involvement of the phosphatase PP2Cm, a recently described member of the branched‐chain α‐keto acid dehydrogenase (BCKDH) complex, in maple syrup urine disease (MSUD). The disease‐causing mutation was identified in a patient with a mild variant phenotype, involving a gene not previously associated with MSUD. SNP array‐based genotyping showed a copy‐neutral homozygous pattern for chromosome 4 compatible with uniparental isodisomy. Mutation analysis of the candidate gene, PPM1K, revealed a homozygous c.417_418delTA change predicted to result in a truncated, unstable protein. No PP2Cm mutant protein was detected in immunocytochemical or Western blot expression analyses. The transient expression of wild‐type PPM1K in PP2Cm‐deficient fibroblasts recovered 35% of normal BCKDH activity. As PP2Cm has been described essential for cell survival, apoptosis and metabolism, the impact of its deficiency on specific metabolic stress variables was evaluated in PP2Cm‐deficient fibroblasts. Increases were seen in ROS levels along with the activation of specific stress‐signaling MAP kinases. Similar to that described for the pyruvate dehydrogenase complex, a defect in the regulation of BCKDH caused the aberrant metabolism of its substrate, contributing to the patient's MSUD phenotype—and perhaps others.

Recent years have seen great advances in our knowledge of congenital disorders of glycosylation (CDG), a clinically and biochemically heterogeneous group of genetic diseases caused by defects in the synthesis (CDG-I) or processing (CDG-II) of glycans that form glycoconjugates. This paper reports a new subtype of non-neurological CDG involving the impaired cytoplasmic biosynthesis of nucleotide sugars needed for glycan biosynthesis. A patient presented with muscle fatigue, elevated creatine kinase, growth hormone deficiency, and first branchial arch syndrome. These findings, together with the abnormal type II plasma transferrin isoform profile detected, was compatible with a CDG. Functional testing and clinical analyses suggested a deficiency in the interconversion of glucose-1-phosphate and glucose-6-phosphate catalyzed by phosphoglucomutase (PGM1), a defect previously described as glycogenosis type XIV (GSDXIV, MIM 612934). PGM1 activity in patient-derived fibroblasts was significantly reduced, as was the quantity of immunoreactive PGM1 protein (Western blot assays). Mutation analysis of PGM1 and subsequent functional analysis investigating transient expression of PGM1 in immortalized patient fibroblasts, followed by ex vivo splicing assays using minigenes, allowed the characterization of two novel pathogenic mutations: c.871G>A (p.Gly291Arg) and c.1144 + 3A>T. The latter represents a severe splicing mutation leading to the out-of-frame skipping of exon 7 and the formation of a truncated protein (p.Arg343fs). MALDI mass spectra of permethylated protein N-glycans from the patient's serum suggested a marked hypoglycosylation defect. The present findings confirm that, in addition to a rare muscular glycolytic defect, PGM1 deficiency causes a non-neurological disorder of glycosylation.

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BackgroundAdvances in the diagnosis and treatment of urea cycle disorders (UCDs) have led to a higher survival rate. The purpose of this study is to describe the characteristics of patients with urea cycle disorders in Spain.MethodsObservational, cross-sectional and multicenter study. Clinical, biochemical and genetic data were collected from patients with UCDs, treated in the metabolic diseases centers in Spain between February 2012 and February 2013, covering the entire Spanish population. Heterozygous mothers of patients with OTC deficiency were only included if they were on treatment due to being symptomatic or having biochemistry abnormalities.Results104 patients from 98 families were included. Ornithine transcarbamylase deficiency was the most frequent condition (64.4%) (61.2% female) followed by type 1 citrullinemia (21.1%) and argininosuccinic aciduria (9.6%). Only 13 patients (12.5%) were diagnosed in a pre-symptomatic state. 63% of the cases presented with type intoxication encephalopathy. The median ammonia level at onset was 298 μmol/L (169-615). The genotype of 75 patients is known, with 18 new mutations having been described. During the data collection period four patients died, three of them in the early days of life. The median current age is 9.96 years (5.29-18), with 25 patients over 18 years of age. Anthropometric data, expressed as median and z-score for the Spanish population is shown. 52.5% of the cases present neurological sequelae, which have been linked to the type of disease, neonatal onset, hepatic failure at diagnosis and ammonia values at diagnosis. 93 patients are following a protein restrictive diet, 0.84 g/kg/day (0.67-1.10), 50 are receiving essential amino acid supplements, 0.25 g/kg/day (0.20-0.45), 58 arginine, 156 mg/kg/day (109-305) and 45 citrulline, 150 mg/kg/day (105-199). 65 patients are being treated with drugs: 4 with sodium benzoate, 50 with sodium phenylbutyrate, 10 with both drugs and 1 with carglumic acid.ConclusionsStudies like this make it possible to analyze the frequency, natural history and clinical practices in the area of rare diseases, with the purpose of knowing the needs of the patients and thus planning their care.

Propionic acidaemia (PA) is an autosomal recessive disorder caused by mutations in either of the PCCA or PCCB genes which encode the α and subunits, respectively, of the mitochondrial enzyme propionyl-CoA carboxylase (PCC). In this work we have examined the biochemical findings and clinical outcome of 37 Spanish PA patients in relation to the mutations found in both PCCA and PCCB genes. We have detected 27 early-onset and 10 late-onset cases, showing remarkably similar biochemical features without relation to either the age of onset of the disease or the defective gene they have. Twenty-one of the patients have so far survived and three of them, now adolescents, present normal development. Different biochemical procedures allowed us to identify the defective gene in 9 PCCA deficient and 28 PCCB deficient patients. Nine putative disease-causing mutations accounting for 77.7% of mutant alleles were identified among PCCA deficient patients, each one carrying a unique genotypic combination. Of PCCB mutant alleles 98% were characterised. Four common mutations (ins/del, E168K, 1170insT and A497V) were found in 38/52 mutant chromosomes investigated, whereas the remainder of the alleles harbour 12 other different mutations. By examining the mutations identified both in PCCA and PCCB genes and the clinical evolution of patients, we have found a good correlation between certain mutations which can be considered as null with a severe phenotype, while certain missense mutations tend to be related to the late and mild forms of the disease. Expression studies, particularly of the missense mutations identified are necessary but other genetic and environmental factors probably contribute to the phenotypic variability observed in PA.

We present an extensive study of the genetic diversity of phenylalanine hydroxylase deficiency in the Spanish phenylketonuria population. We have analysed 195 PKU patients by DGGE analysis identifying 67 different mutations which represent 89% of the total mutant chromosomes. Seventeen mutations first described in Spain have not yet been detected elsewhere; ten of these are reported here for the first time. The clinical significance of this high genetic heterogeneity was examined by analysing the genotype-phenotype correlations, mainly focusing on the mild hyperphenylalaninaemia (MHP) phenotype. The genotypes found in a group of 93 MHP patients, the largest analysed so far, are described in detail, as well as the relative frequencies of the MHP mutations identified. From the total pool of mutations, 27 can be considered severe, 18 can be defined as mild and 13 as associated with MHP. The prevalent mutations correspond to one severe mutation (IVS10nt-11), one MHP mutation (A403V) and two mild mutations (I65T and V388M). The high frequency of mutations with a low degree of severity can explain the relatively higher prevalence of MHP and mild PKU phenotypes in Spain compared with Northern European populations. We have looked at the geographical distribution in Spain of the more common mutations, finding evidence of local mutation clustering, which could be the result of differences in the ethnic background and/or of genetic drift within each region.

Methylmalonic acidaemia (MMA) is a genetic disorder caused by defects in methylmalonyl-CoA mutase or in any of the different proteins involved in the synthesis of adenosylcobalamin. The aim of this work was to examine the biochemical and clinical phenotype of 32 MMA patients according to their genotype, and to study the mutant mRNA stability by real-time PCR analysis. Using cellular and biochemical methods, we classified our patient cohort as having the MMA forms mut (n = 19), cblA (n = 9) and cblB (n = 4). All the mut (0) and some of the cblB patients had the most severe clinical and biochemical manifestations, displaying non-inducible propionate incorporation in the presence of hydroxocobalamin (OHCbl) in vitro and high plasma odd-numbered long-chain fatty acid (OLCFA) concentrations under dietary therapy. In contrast, mut (-) and cblA patients exhibited a milder phenotype with propionate incorporation enhanced by OHCbl and normal OLCFA levels under dietary therapy. No missense mutations identified in the MUT gene, including mut (0) and mut (-) changes, affected mRNA stability. A new sequence variation (c.562G>C) in the MMAA gene was identified. Most of the cblA patients carried premature termination codons (PTC) in both alleles. Interestingly, the transcripts containing the PTC mutations were insensitive to nonsense-mediated decay (NMD).