Sudden cardiac death due to deficiency of the mitochondrial inorganic pyrophosphatase PPA2

We have used whole exome sequencing to identify biallelic missense mutations in the nuclearencoded mitochondrial inorganic pyrophosphatase (PPA2) in ten individuals from four unrelated pedigrees that are associated with mitochondrial disease. These individuals show a range of severity, indicating that PPA2 mutations may cause a spectrum of mitochondrial disease phenotypes. Severe symptoms include seizures, lactic acidosis and cardiac arrhythmia and death within days of birth. In the index family, presentation was milder and manifested as cardiac fibrosis and an exquisite sensitivity to alcohol, leading to sudden arrhythmic cardiac death in the second decade of life. Comparison of normal and mutated PPA2 containing mitochondria from fibroblasts showed the activity of inorganic pyrophosphatase significantly reduced in affected individuals. Recombinant PPA2 enzymes modeling hypomorphic missense mutations had decreased activity that correlated with disease severity. These findings confirm the pathogenicity of PPA2 mutations, and suggest that PPA2 is a new cardiomyopathy-associated protein, which has a greater physiological importance in mitochondrial function than previously recognized

Mutation and biochemical analysis of 19 probands with mut0 and 13 with mut- methylmalonic aciduria : identification of seven novel mutations

Isolated methylmalonic acidurias (MMA-urias) comprise a group of rare autosomal recessively inherited disorders characterised by accumulation of MMA in urine and other body fluids, resulting from deficient activity of the mitochondrial enzyme methylmalonyl-CoA mutase (MCM). Isolated MMA-uria results from either MCM apoenzyme defects (mut(0) and mut(-)) or defects in synthesis of its cofactor 5-deoxyadenosylcobalamin, i.e. cblA, cblB and cblD-variant 2. To date various studies have identified 171 disease-causing mutations in the MCM gene (MUT). We report mutation analysis in 32 probands with mut MMA-uria including 13 probands with a mut(-) defect. Sixty two of 64 possible mutant alleles were identified, seven of which were novel missense alleles. We found three novel mutations (c.427C<T/p.H143Y; c.862T<C/p.S288P; c.1361G<A/p.G454E) among 19 probands with a mut(0) defect and four novel mutations (c.299A<G/p.Y100C; c.1031C<T/p.S344F; c.1097A<G/p.N366S; c.2081G<T/p.R694L) among 13 probands with a mut(-) defect. Our study provides evidence that the p.Y100C, p.R108H, p.N366S, p.V633G, p.R694W, p.R694L and p.M700K mutations are associated with a mut(-) phenotype

Pyruvate Dehydrogenase Phosphatase Deficiency: Identification of the First Mutation in Two Brothers and Restoration of Activity by Protein Complementation

Context: Pyruvate dehydrogenase phosphatase (PDP) deficiency has been previously reported as an enzymopathy, but the genetic basis for such a defect has never been established. Objective: The aim of this study was to identify the cause of the defect in two patients who presented with PDP deficiency. Patients: We studied two brothers of consanguineous parents who presented with neonatal hypotonia, elevated lactate, and less than 25% native pyruvate dehydrogenase complex (PDHc) activity in skin fibroblasts compared with controls. The activity of the complex could be restored to normal values by preincubation of the cells with dichloroacetate or by treating cell extracts with calcium. Results: These two individuals were found to be homozygous for a 3-bp deletion in the coding sequence of the PDP isoform 1 (PDP1), which removes the amino acid residue leucine from position 213 of the protein. A recombinant version of this protein was synthesized and found to have a very reduced (<5%) ability to activate purified PDHc. Reduced steady-state levels of PDP1 in the patient’s fibroblasts coupled with the low catalytic activity of the mutant PDP1 resulted in native PDHc activity being reduced, but this could be corrected by the addition of recombinant PDP1 (wild type). Conclusion: We have identified mutations in PDP1 in two brothers with PDP deficiency and have proven that the mutation is disease-causing. This is the first demonstration of human disease due to a mutation in PDP1

Long-Term Outcome in Methylmalonic Acidurias Is Influenced by the Underlying Defect (mut0, mut−, cblA, cblB)

Isolated methylmalonic acidurias comprise a heterogeneous group of inborn errors of metabolism caused by defects of methylmalonyl-CoA mutase (MCM) (mut0, mut–) or deficient synthesis of its cofactor 5′-deoxyadenosylcobalamin (AdoCbl) (cblA, cblB). The aim of this study was to compare the long-term outcome in patients from these four enzymatic subgroups. Eighty-three patients with isolated methylmalonic acidurias (age 7–33 y) born between 1971 and 1997 were enzymatically characterized and prospectively followed to evaluate the long-term outcome (median follow-up period, 18 y). Patients with mut0 (n = 42), mut− (n = 10), cblA (n = 20), and cblB (n = 11) defects were included into the study. Thirty patients (37%) died, and 26 patients survived with a severe or moderate neurologic handicap (31%), whereas 27 patients (32%) remained neurologically uncompromised. Chronic renal failure (CRF) was found most frequently in mut0 (61%) and cblB patients (66%), and was predicted by the urinary excretion of methylmalonic acid (MMA) before CRF. Overall, patients with mut0 and cblB defects had an earlier onset of symptoms, a higher frequency of complications and deaths, and a more pronounced urinary excretion of MMA than those with mut− and cblA defects. In addition, long-term outcome was dependent on the age cohort and cobalamin responsiveness

Delayed-onset profound biotinidase deficiency

Children with biotinidase deficiency usually exhibit symptoms at several months to years of age. We describe four children who had symptoms later in childhood or during adolescence; they had motor limb weakness, spastic paresis, and eye problems, such as loss of visual acuity and scotomata, rather than the more characteristic symptoms observed in young untreated children with the disorder. These older children each have different mutations, but they are the same as those of children who have exhibited symptoms at an early age. Biotinidase deficiency should be considered in older children who suddenly experience limb weakness and/or spastic paresis and eye symptoms

The molecular basis of human 3-methylcrotonyl-CoA carboxylase deficiency

Isolated biotin-resistant 3-methylcrotonyl-CoA carboxylase (MCC) deficiency is an autosomal recessive disorder of leucine catabolism that appears to be the most frequent organic aciduria detected in tandem mass spectrometry–based neonatal screening programs. The phenotype is variable, ranging from neonatal onset with severe neurological involvement to asymptomatic adults. MCC is a heteromeric mitochondrial enzyme composed of biotin-containing α subunits and smaller β subunits. Here, we report cloning of MCCA and MCCB cDNAs and the organization of their structural genes. We show that a series of 14 MCC-deficient probands defines two complementation groups, CG1 and 2, resulting from mutations in MCCB and MCCA, respectively. We identify five MCCA and nine MCCB mutant alleles and show that missense mutations in each result in loss of function