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Renkema G.H.,Radboud University Nijmegen | Renkema G.H.,Center for Systems Biology and Bioenergetics | Wortmann S.B.,Radboud University Nijmegen | Smeets R.J.,Radboud University Nijmegen | And 9 more authors.
European Journal of Human Genetics | Year: 2015

Defects in complex II of the mitochondrial respiratory chain are a rare cause of mitochondrial disorders. Underlying autosomal-recessive genetic defects are found in most of the 'SDHx' genes encoding complex II (SDHA, SDHB, SDHC, and SDHD) and its assembly factors. Interestingly, SDHx genes also function as tumor suppressor genes in hereditary paragangliomas, pheochromocytomas, and gastrointestinal stromal tumors. In these cases, the affected patients are carrier of a heterozygeous SDHx germline mutation. Until now, mutations in SDHx associated with mitochondrial disease have not been reported in association with hereditary tumors and vice versa. Here, we characterize four patients with isolated complex II deficiency caused by mutations in SDHA presenting with multisystem mitochondrial disease including Leigh syndrome (LS) and/or leukodystrophy. Molecular genetic analysis revealed three novel mutations in SDHA. Two mutations (c.64-2A>G and c.1065-3C>A) affect mRNA splicing and result in loss of protein expression. These are the first mutations described affecting SDHA splicing. For the third new mutation, c.565T>G, we show that it severely affects enzyme activity. Its pathogenicity was confirmed by lentiviral complementation experiments on the fibroblasts of patients carrying this mutation. It is of special interest that one of our LS patients harbored the c.91C>T (p.Arg31∗) mutation that was previously only reported in association with paragangliomas and pheochromocytomas, tightening the gap between these two rare disorders. As tumor screening is recommended for SDHx mutation carriers, this should also be considered for patients with mitochondrial disorders and their family members. © 2015 Macmillan Publishers Limited All rights reserved.


Wortmann S.B.,Radboud University Nijmegen | Wortmann S.B.,Institute of Genetic and Metabolic Disease IGMD | Vaz F.M.,Metabolic | Gardeitchik T.,Radboud University Nijmegen | And 48 more authors.
Nature Genetics | Year: 2012

Using exome sequencing, we identify SERAC1 mutations as the cause of MEGDEL syndrome, a recessive disorder of dystonia and deafness with Leigh-like syndrome, impaired oxidative phosphorylation and 3-methylglutaconic aciduria. We localized SERAC1 at the interface between the mitochondria and the endoplasmic reticulum in the mitochondria-associated membrane fraction that is essential for phospholipid exchange. A phospholipid analysis in patient fibroblasts showed elevated concentrations of phosphatidylglycerol-34:1 (where the species nomenclature denotes the number of carbon atoms in the two acyl chains:number of double bonds in the two acyl groups) and decreased concentrations of phosphatidylglycerol-36:1 species, resulting in an altered cardiolipin subspecies composition. We also detected low concentrations of bis(monoacyl-glycerol)-phosphate, leading to the accumulation of free cholesterol, as shown by abnormal filipin staining. Complementation of patient fibroblasts with wild-type human SERAC1 by lentiviral infection led to a decrease and partial normalization of the mean ratio of phosphatidylglycerol-34: 1 to phosphatidylglycerol-36:1. Our data identify SERAC1 as a key player in the phosphatidylglycerol remodeling that is essential for both mitochondrial function and intracellular cholesterol trafficking. © 2012 Nature America, Inc. All rights reserved.


Schirris T.J.J.,Radboud University Nijmegen | Schirris T.J.J.,Center for Systems Biology and Bioenergetics | Ritschel T.,Radboud University Nijmegen | Bilos A.,Radboud University Nijmegen | And 4 more authors.
Molecular Pharmaceutics | Year: 2015

Statins are cholesterol-lowering drugs that have proven to be effective in lowering the risk of major cardiovascular events. Although well tolerated, statin-induced myopathies are the most common side effects. Compared to their pharmacologically active acid form, statin lactones are more potent inducers of toxicity. They can be formed by glucuronidation mediated by uridine 5′-diphospho-glucuronosyltransferases (UGTs), but a systematic characterization of subtype specificity and kinetics of lactonization is lacking. Here, we demonstrate for six clinically relevant statins that only UGT1A1, 1A3, and 2B7 contribute significantly to their lactonization. UGT1A3 appeared to have the highest lactonization capacity with marked differences in statin conversion rates: pitavastatin 蠑 atorvastatin > cerivastatin > lovastatin > rosuvastatin (simvastatin not converted). Using in silico modeling we could identify a probable statin interaction region in the UGT binding pocket. Polymorphisms in these regions of UGT1A1, 1A3, and 2B7 may be a contributing factor in statin-induced myopathies, which could be used in personalization of statin therapy with improved safety. © 2015 American Chemical Society.

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