[Show abstract][Hide abstract] ABSTRACT: Discovering the molecular basis of mitochondrial respiratory chain disease is challenging given the large number of both mitochondrial and nuclear genes that are involved. We report a strategy of focused candidate gene prediction, high-throughput sequencing and experimental validation to uncover the molecular basis of mitochondrial complex I disorders. We created seven pools of DNA from a cohort of 103 cases and 42 healthy controls and then performed deep sequencing of 103 candidate genes to identify 151 rare variants that were predicted to affect protein function. We established genetic diagnoses in 13 of 60 previously unsolved cases using confirmatory experiments, including cDNA complementation to show that mutations in NUBPL and FOXRED1 can cause complex I deficiency. Our study illustrates how large-scale sequencing, coupled with functional prediction and experimental validation, can be used to identify causal mutations in individual cases.
[Show abstract][Hide abstract] ABSTRACT: Premature ovarian failure (POF) results in menopause before the age of 40. Recently, mutations in the catalytic subunit of mitochondrial DNA polymerase gamma (POLG) were shown to segregate with POF in families with progressive external ophthalmoplegia (PEO) and multiple large-scale rearrangements of mitochondrial DNA (mtDNA).
A patient, mother and maternal grandmother are described, all presenting with POF and PEO. The mother developed parkinsonism in her sixth decade. Normal mtDNA sequence excluded mitochondrial inheritance. Sequence analysis of polymerase gamma revealed a dominant Y955C mutation that segregated with disease. Southern blot analysis demonstrated mtDNA depletion in fibroblasts (43% of controls). In contrast, multiple rearrangements of mtDNA were seen in skeletal muscle, consistent with the relative sparing of nuclear-encoded complex II activity compared with other respiratory chain enzymes. Immunoblotting of native gels showed that DNA polymerase gamma stability was not affected, whereas a reverse-transcriptase primer-extension assay suggested a trend towards reduced polymerase activity in fibroblasts.
This study confirms that POLG mutations can segregate with POF and parkinsonism and demonstrates for the first time that the Y955C mutation can lead to mtDNA depletion. Future screening projects will determine the frequency with which POLG is involved in the aetiology of POF and its impact on reproductive counselling.
Human Reproduction 11/2006; 21(10):2467-73. · 4.59 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We describe 7 Polynesian babies with a unique severe form of holocarboxylase synthetase deficiency characterized by antenatal growth retardation, subependymal cysts, only partial response to biotin, and a poor outcome.
Journal of Pediatrics 08/2005; 147(1):115-8. · 3.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An infant presented with massive hyperchylomicronemia and a severe encephalopathy. MRI showed marked lipid deposition throughout the brain. Despite the normalization of the biochemistry, there was little clinical improvement, and at 18 months of age she has severe developmental delay, a strikingly abnormal MRI. Apolipoprotein C-II, the lipoprotein on chylomicrons responsible for the activation of lipoprotein lipase, was not detectable in blood. Analysis of the APO C-II gene revealed a novel homozygous point mutation, 1118C-->A. Subsequently, another sibling has been born with the same homozygous mutation and similar biochemistry but, perhaps because of early treatment, a normal neurological outcome.
Annals of Neurology 06/2003; 53(6):807-10. · 11.91 Impact Factor