Mercedes Martínez-Pardo

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.

A novel congenital disorder of glycosylation type without central nervous system involvement caused by mutations in the phosphoglucomutase 1 gene

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.

Early-onset multisystem mitochondrial disorder caused by a nonsense mutation in the mitochondrial DNA cytochrome C oxidase II gene.

We report the first nonsense mutation (G7896A) in the mtDNA gene for subunit II of cytochrome c oxidase (COX) in a patient with early‐onset multisystem disease and COX deficiency in muscle. The mutation was heteroplasmic in muscle, blood, and fibroblasts from the patient and abundantly present in COX‐deficient fibers, but less abundant in COX‐positive fibers; it was not found in blood samples from the patients asymptomatic maternal relatives. Immunoblot analysis showed a reduced concentration of both COX II and COX I polypeptides, suggesting impaired assembly of COX holoenzyme.

Physical development in patients with phenylketonuria on dietary treatment: A retrospective study

OBJECTIVES To evaluate the growth and physical development in patients with phenylalanine hydroxylase deficiency who follow exclusively dietary treatment. METHODS Anthropometric measurements of 160 patients with hyperphenylalaninemia who were followed at our center over a 25 year period were obtained. Only patients treated exclusively with a protein-restrictive diet supplemented with amino acid mixtures were included. Height, weight and body mass index were measured at birth, at diagnosis, at 6 and 12 months of age, and annually until 18 years of age in patients with phenylketonuria or until 9 years of age in patients with mild hyperphenylalaninemia and compared to official national reference values. The final height of PKU patients was also compared to their expected family height. RESULTS The analysis of z scores suggested no significant differences in physical development between PKU patients and the healthy population during the study period. The final height of PKU patients revealed that they were 2 to 4 cm taller than expected when compared to the mean family height (p<0.001). The mean weight and BMI at puberty suggested that many patients with severe PKU, but not other phenotypes, were overweight during this period. CONCLUSION Physical development can be optimal in PKU patients regardless of their phenotype and the severity of the diet. A tendency to excessive weight gain is seen in adolescence in the most severe phenotypes.

A Novel Regulatory Defect in the Branched-Chain α-Keto Acid Dehydrogenase Complex Due to a Mutation in the PPM1K Gene Causes a Mild Variant Phenotype of Maple Syrup Urine Disease

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 patients MSUD phenotype—and perhaps others.

Marked mitochondrial DNA depletion associated with a novel SUCLG1 gene mutation resulting in lethal neonatal acidosis, multi-organ failure, and interrupted aortic arch

The aim of this study was to identify the causative genetic lesion in two apparently unrelated newborns having lethal lactic acidosis, multi-organ failure and congenital malformations including interrupted aortic arch, who exhibited mild methylmalonic aciduria, combined mitochondrial respiratory chain deficiency, and marked muscle mitochondrial DNA depletion. A novel mutation in the SUCLG1 gene was identified. Phenotype severity in Succinate-CoA ligase dysfunction appears to be more correlated to the muscle mtDNA content than to the tissue distribution of the heterodimer subunits. Prominent impairment of mitochondrial respiratory chain may result in deep ravages in developmental tissues leading to multiple organ failure and malformations.

Hyperammonaemia as a cause of psychosis in an adolescent

Diseases that cause hyperammonaemia usually appear during the neonatal period or during the first months of life as severe neurological metabolic distress. In some cases, as the one reported here, the age of onset and initial symptoms are non-specific and the episodes of acute metabolic encephalopathy may be attributed to encephalitis, poisoning or psychiatric problems. Our patient had N-acetyl glutamate synthetase deficiency due to a lack of activation by L-arginine. Treatment with N-carbamylglutamate was successful in maintaining normal ammonia levels. Conclusion: we emphasise the importance of measuring ammonia levels in patients with neurological or psychiatric symptoms as part of their diagnostic work-up.

Phenotype distribution in the Spanish phenylketonuria population and related genotypes

Phenylketonuria (PKU, McKusick 261600) is an autosomal recessive disorder caused by a deficiency of the liver enzyme phenylalanine hydroxylase (PAH, EC1.14.16.1). In the last decade, biochemical studies have revealed that PAH deficiency is phenotypically heterogeneous, and four PKU phenotypes have been described: severe, moderate, mild and non-PKU hyperphenylalaninaemia (HPA); according to phenylalanine tolerance and plasma phenylalanine levels at diagnosis (Guttler et al 1993). Up to now, more than 70 mutations associated with the PAH gene have been described and in vitro expression of these mutations has allowed correlation with the different phenotypes (Eisensmith and Woo 1992)

Estudio epidemiológico de las enfermedades metabólicas con homocistinuria en España

OBJECTIVES To determine the prevalence of homocystinuria in Spain and to establish the measures and mechanisms to ensure its prevention, diagnosis and treatment. MATERIAL AND METHODS A national cross-sectional survey was conducted by means of a questionnaire sent to 35 hospitals in which children and adult patients are treated. RESULTS Using the questionnaires submitted by 25 physicians from 16 centres, 75 patients were identified: 41 transsulphuration defects (one deceased), 27 remethylation (six deaths) and 7 without a syndromic diagnosis. The age at diagnosis varied widely, and 18 cases had more than one sibling affected. The more severe clinical manifestations involved the patients with remethylation defects. There was a high percentage of cognitive impairment, followed by lens diseases. Almost half of the patients had neurological disorders. There was increased vascular involvement in CBS-deficient adults. The therapeutic options most used were, folic acid, hydroxycobalamin and betaine. CONCLUSIONS In view of these results and especially the small number of CBS deficiencies detected, we conclude that there is a need to introduce newborn screening for classical homocystinuria and ensure implementation of an appropriate diagnostic workup in all patients at risk.

Déficit de glicerol kinasa en el adulto: hipertrigliceridemia resistente a tratamiento dietético y farmacológico

Caso clinico: presentamos un paciente varon de 85 anos con polidipsia, poliuria e hipertrigliceridemia severa de 27 anos de evolucion, sin pancreatitis, persistente y resistente a tratamientos dietetico y farmacologico. Se diagnostico de hiperglicerolemia por defi cit de glicerol kinasa (GKD) en base a: suero transparente no lipemico, aumento de glicerol en plasma y orina, sin aumento de glicerol 3 fosfato y delecion, no descrita previamente, en el gen de la glicerol kinasa. Discusion: un tratamiento dietetico correcto con comidas frecuentes y rico en carbohidratos complejos, sin medicacion, mejoro la sintomatologia.