J.M.F. Trijbels

Mutant NDUFV1 subunit of mitochondrial complex I causes leukodystrophy and myoclonic epilepsy.

Mutant NDUFV1xa0subunit of mitochondrial complex I causes leukodystrophy and myoclonic epilepsy

Human mitochondrial transmembrane metabolite carriers: Tissue distribution and its implication for mitochondrial disorders

Mitochondrial transmembrane carrier deficiencies are a recently discovered group of disorders, belonging to the so-called mitochondriocytopathies. We examined the human tissue distribution of carriers which are involved in the process of oxidative phosphorylation (adenine nucleotide translocator, phosphate carrier, and voltage-dependent anion channel) and some mitochondrial substrate carriers (2-oxoglutarate carrier, carnitine-acylcarnitine carrier, and citrate carrier). The tissue distribution on mRNA level of mitochondrial transport proteins appears to be roughly in correlation with the dependence of these tissues on mitochondrial energy production capacity. In general the main mRNA expression of carriers involved in mitochondrial energy metabolism occurs in skeletal muscle and heart. Expression in liver and pancreas differs between carriers. Expression in brain, placenta, lung, and kidney is lower than in the other tissues. Western and Northern blotting experiments show a comparable HVDAC1 protein and mRNA distribution for the tested tissues. Patients studies showed that cultured skin fibroblasts may not be a reliable alternative for skeletal muscle in screening for human mitochondrial carrier defects.

A 31 bp VNTR in the cystathionine beta-synthase (CBS) gene is associated with reduced CBS activity and elevated post-load homocysteine levels.

Molecular defects in genes encoding enzymes involved in homocysteine metabolism may account for mild hyperhomocysteinaemia, an independent and graded risk factor for cardiovascular disease (CVD). Although heterozygosity for cystathionine β-synthase (CBS) deficiency has been excluded as a major genetic cause of mild hyperhomocysteinaemia in vascular disease, mutations in (non-)coding DNA sequences may lead to a mildly decreased CBS expression and, consequently, to elevated plasma homocysteine levels. We assessed the association between a 31 bp VNTR, that spans the exon 13-intron 13 boundary of the CBS gene, and fasting, post-methionine load and increase upon methionine load plasma homocysteine levels in 190 patients with arterial occlusive disease, and in 381 controls. The 31u2009bp VNTR consists of 16, 17, 18, 19 or 21 repeat units and shows a significant increase in plasma homocysteine concentrations with an increasing number of repeat elements, in particular after methionine loading. In 26 vascular disease patients the relationship between this 31u2009bp VNTR and CBS enzyme activity in cultured fibroblasts was studied. The CBS enzyme activity decreased with increasing number of repeat units of the 31 bp VNTR. RT–PCR experiments showed evidence of alternative splicing at the exon 13-intron 13 splice junction site. The 31u2009bp VNTR in the CBS gene is associated with post-methionine load hyperhomocysteinaemia that may predispose individuals to an increased risk of cardiovascular diseases.

Carnitine-acylcarnitine carrier deficiency: identification of the molecular defect in a patient

M. HUIZING1, U. WENDEL2, W. RUITENBEEK1*, V. IACOBAZZI3, L. IJLST4, P. VEENHUIZEN1, P. SAVELKOUL1, L. P. VAN DEN HEUVEL1, J. A. M. SMEITINK1, R. J. A. WANDERS4, J. M. F. TRIJBELS1 and F. PALMIERI3 of 1University Hospital, Department Pediatrics, Nijmegen, T he Netherlands ; of of 2University Hospital, Department Pediatrics, Dux8e sseldorf, Germany ; 3University of of Bari, Department Pharmaco-Biology, Bari, Italy ; 4University Amsterdam, of Clinical Chemistry and Departments Pediatrics, Amsterdam, T he Netherlands

Importance of mitochondrial transmembrane processes in human mitochondriopathies

In a substantial group of subjects suspected to have a mitochondriopathy no defect in the mitochondrial energy metabolism (pyruvate dehydrogenase complex or respiratory chain complexes) can be demonstrated. At least in some of these subjects it seems justified to consider a defect in one of the proteins which mediate the transport of several ions and substrates across the mitochondrial membranes. Of particular interest are proteins which are directly involved in the process of oxidative phosphorylation, such as the adenine nucleotide translocator (ANT) and the phosphate carrier (PiC). However, defects in transmembrane ion transporters also may induce impaired energy metabolism probably as a result of osmotic disturbances within the mitochondrial matrix. In this respect, the voltage-dependent anion channel (VDAC) and other ion channels have to be taken into consideration. Here we review the still incomplete knowledge of the occurrence of ANT, PiC, VDAC, cation channels, and a few substrate carriers in human tissues, as well as their possible role in pathology.