MELAS: Clinical features, biochemistry, and molecular genetics
ABSTRACT We studied 23 patients with clinically defined mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS), 25 oligosymptomatic or asymptomatic maternal relatives, and 50 mitochondrial disease control subjects for the presence of a previously reported heteroplasmic point mutation at nt 3,243 in the transfer RNALeu(UUR) gene of mitochondrial DNA. We found a high concordance between clinical diagnosis of MELAS and transfer RNALeu(UUR) mutation, which was present in 21 of the 23 patients with MELAS, all 11 oligosymptomatic and 12 of 14 asymptomatic relatives, but in only five of 50 patients without MELAS. The proportion of mutant genomes in muscle ranged from 56 to 95% and was significantly higher in the patients with MELAS than in their oligosymptomatic or asymptomatic relatives. In subjects in whom both muscle and blood were studied, the percentage of mutations was significantly lower in blood and was not detected in three of 12 asymptomatic relatives. The activities of complexes I + III, II + III, and IV were decreased in muscle biopsies harboring the mutation, but there was no clear correlation between percentage of mutant mitochondrial DNAs and severity of the biochemical defect.
SourceAvailable from: Duur K Aanen[Show abstract] [Hide abstract]
ABSTRACT: The peculiar biology of mitochondrial DNA (mtDNA) potentially has detrimental consequences for organismal health and lifespan. Typically, eukaryotic cells contain multiple mitochondria, each with multiple mtDNA genomes. The high copy number of mtDNA implies that selection on mtDNA functionality is relaxed. Furthermore, because mtDNA replication is not strictly regulated, within-cell selection may favour mtDNA variants with a replication advantage, but a deleterious effect on cell fitness. The opportunities for selfish mtDNA mutations to spread are restricted by various organism-level adaptations, such as uniparental transmission, germline mtDNA bottlenecks, germline selection and, during somatic growth, regular alternation between fusion and fission of mitochondria. These mechanisms are all hypothesized to maintain functional mtDNA. However, the strength of selection for maintenance of functional mtDNA progressively declines with age, resulting in age-related diseases. Furthermore, organismal adaptations that most probably evolved to restrict the opportunities for selfish mtDNA create secondary problems. Owing to predominantly maternal mtDNA transmission, recombination among mtDNA from different individuals is highly restricted or absent, reducing the scope for repair. Moreover, maternal inheritance precludes selection against mtDNA variants with male-specific effects. We finish by discussing the consequences of life-history differences among taxa with respect to mtDNA evolution and make a case for the use of microorganisms to experimentally manipulate levels of selection.Philosophical Transactions of The Royal Society B Biological Sciences 07/2014; 369(1646). DOI:10.1098/rstb.2013.0438 · 6.31 Impact Factor
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ABSTRACT: Mitochondrial diseases are potentially severe, incurable diseases resulting from dysfunctional mitochondria. Several important mitochondrial diseases are caused by mutations in mitochondrial DNA (mtDNA), the genetic material contained within mitochondria, which is maternally inherited. Classical and modern therapeutic approaches exist to address the inheritance of mtDNA disease, but are potentially complicated by the fact that cellular mtDNA populations evolve according to poorly-understood dynamics during development and organismal lifetimes. We review these therapeutic approaches and models of mtDNA dynamics during development, and discuss the implications of recent results from these models for modern mtDNA therapies. We particularly highlight mtDNA segregation-differences in proliferative rates between different mtDNA haplotypes-as a potential and underexplored issue in such therapies. However, straightforward strategies exist to combat this and other potential therapeutic problems. In particular, we describe haplotype matching as an approach with the power to potentially ameliorate any expected issues from mtDNA incompatibility. © The Author 2014. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology.Molecular Human Reproduction 11/2014; DOI:10.1093/molehr/gau090 · 3.48 Impact Factor
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ABSTRACT: Mitochondrial diseases are multiorgan system disorders and the brain is the most commonly affected organ. The high-energy requirement of the brain leaves it vulnerable to energy failure. All components of the neuraxis including muscle, the neuromuscular junction, peripheral nerve, spinal cord, and brain can be affected. Genetic mitochondrial disease can be caused by nuclear gene defects and mitochondrial DNA defects. Mitochondrial medicine is rapidly expanding as exome and mtDNA sequencing is identifying new gene defects on a daily basis. This review will focus on primary genetic mitochondrial diseases that impair energy production and affect the nervous system, pathophysiology of disease, classical phenotypes, diagnosis, and treatment.Seminars in Neurology 07/2014; 34(3):321-40. DOI:10.1055/s-0034-1386770 · 1.78 Impact Factor