3-Methylglutaconic aciduria--lessons from 50 genes and 977 patients.

Elevated urinary excretion of 3-methylglutaconic acid is considered rare in patients suspected of a metabolic disorder. In 3-methylglutaconyl-CoA hydratase deficiency (mutations in AUH), it derives from leucine degradation. In all other disorders with 3-methylglutaconic aciduria the origin is unknown, yet mitochondrial dysfunction is thought to be the common denominator. We investigate the biochemical, clinical and genetic data of 388 patients referred to our centre under suspicion of a metabolic disorder showing 3-methylglutaconic aciduria in routine metabolic screening. Furthermore, we investigate 591 patients with 50 different, genetically proven, mitochondrial disorders for the presence of 3-methylglutaconic aciduria. Three percent of all urine samples of the patients referred showed 3-methylglutaconic aciduria, often in correlation with disorders not reported earlier in association with 3-methylglutaconic aciduria (e.g. organic acidurias, urea cycle disorders, haematological and neuromuscular disorders). In the patient cohort with genetically proven mitochondrial disorders 11% presented 3-methylglutaconic aciduria. It was more frequently seen in ATPase related disorders, with mitochondrial DNA depletion or deletion, but not in patients with single respiratory chain complex deficiencies. Besides, it was a consistent feature of patients with mutations in TAZ, SERAC1, OPA3, DNAJC19 and TMEM70 accounting for mitochondrial membrane related pathology. 3-methylglutaconic aciduria is found quite frequently in patients suspected of a metabolic disorder, and mitochondrial dysfunction is indeed a common denominator. It is only a discriminative feature of patients with mutations in AUH, TAZ, SERAC1, OPA3, DNAJC19 TMEM70. These conditions should therefore be referred to as inborn errors of metabolism with 3-methylglutaconic aciduria as discriminative feature.

Novel mutations in the NDUFS1 gene cause low residual activities in human complex I deficiencies.

Mitochondrial complex I deficiency is the most frequently encountered defect of the oxidative phosphorylation system. To identify the genetic cause of the complex I deficiency, we screened the gene encoding the NDUFS1 subunit. We report 3 patients with low residual complex I activity expressed in cultured fibroblasts, which displayed novel mutations in the NDUFS1 gene. One mutation introduces a premature stop codon, 3 mutations cause a substitution of amino acids and another mutation a deletion of one amino acid. The fibroblasts of the patients display a decreased amount and activity of complex I. In addition, a disturbed assembly pattern was observed. These results suggest that NDUFS1 is a prime candidate to screen for disease-causing mutations in patients with a very low residual complex I activity in cultured fibroblasts.

Genetic disorders in complement (regulating) genes in patients with atypical haemolytic uraemic syndrome (aHUS).

BACKGROUND: Atypical HUS (aHUS) is thought to be caused by predisposing mutations in genes encoding complement (regulating) proteins, such as Factor H (CFH), Factor I (IF), membrane co-factor protein (MCP) and Factor B (FB), or by auto-antibodies against CFH (alphaFH) in combination with a homozygous polymorphic deletion of the genes encoding Complement Factor H-related 1 and 3 (DeltaCFHR1/3). The clinical impact of this knowledge is high, as it might be a prognostic factor for the outcome of renal transplantations and kidney donations. METHODS: Mutational screening, by means of PCR and DNA sequencing, is performed in the above-mentioned genes in a group of 72 aHUS patients. Also, the presence of alphaFH and DeltaCFHR1/3 was tested in patients and controls. RESULTS: In 23 patients, a genetic aberration in at least one gene or the presence of alphaFH was found. A heterozygous mutation was observed in CFH in nine patients, in IF in seven patients and in MCP in three patients. No mutations were observed in FB. Seven patients presented alphaFH, of whom five also carried DeltaCFHR1/3. Three patients carried a combined mutation (two patients: IF and MCP; one patient: IF, alphaFH and DeltaCFHR1/3). A significant difference between patients and controls was detected for the presence of all three associated polymorphisms in CFH. CONCLUSIONS: Genetic abnormalities or the presence of alphaFH were detected in 31.9% of the aHUS patients. Furthermore, bigenic mutations were present, indicating that routine DNA mutation analysis of all complement factors associated with aHUS is important.

Multiple oxidative phosphorylation deficiencies in severe childhood multi-system disorders due to polymerase gamma (POLG1) mutations.

Failure to thrive, feeding difficulties, variable forms of infantile epilepsy or psychomotor developmental delay and hypotonia were the most frequent clinical disease presentations in eight children with combined oxidative phosphorylation enzyme complex deficiencies carrying mutations in the polymerase gamma (POLG1) gene. Five out of eight patients developed severe liver dysfunction during the course of the disease. Three of these patients fulfilled the disease criteria for Alpers syndrome. Most children showed deficiencies of respiratory chain enzyme complexes I and III, in combination with complex II, complex IV and/or PDHc in muscle, whereas in fibroblasts normal enzyme activities were measured. All children carried homozygous or compound heterozygous mutations in the POLG1 gene, including two novel mutations in association with mtDNA depletion. Conclusion We suggest performing POLG1 mutation analysis in children with combined oxidative phosphorylation deficiencies in muscle, even if the clinical picture is not Alpers syndrome.

Sequence analysis of the structural nuclear encoded subunits and assembly genes of cytochrome c oxidase in a cohort of 10 isolated complex IV-deficient patients revealed five mutations.

The mitochondrial oxidative phosphorylation system is composed of five multiprotein complexes. The fourth complex of this system, cytochrome c oxidase (complex IV), consists of 13 subunits: 3 encoded by mitochondrial DNA and 10 encoded by the nuclear genome. Patients with an isolated complex IV deficiency frequently harbor mutations in nuclear genes encoding for proteins necessary for the assembly of the complex. Strikingly, until now, no mutations have been detected in the nuclear encoded structural subunits of complex IV in these patients. We report the results of a mutational analysis study in patients with isolated complex IV deficiency screened for mutations in all structural genes as well as assembly genes known to cause complex IV deficiency. Four patients carried mutations in the complex IV assembly gene SURF1. One patient harbored a mutation in the COX10 gene involved in heme A synthesis. Mutations in the 10 nuclear encoded structural genes were not present.