Genetic risk factors and disease mechanisms in mitochondrial optic neuropathy

Abstract

Mitochondrial vitality is dependent upon continued cooperation between nuclear (nDNA) and mitochondrial genomes (mtDNA) and defects in either genome can result in a broad spectrum of human disease. Leber’s Hereditary Optic Neuropathy (LHON) is an inherited blindness caused by the selective loss of retinal ganglion cells (RGCs) which predominantly affects young males. In 90% of LHON, cases harbour one of three primary mutations, m.11778G>A, m.3460G>A and m.14484T>C, which affect Complex I subunits of the electron transport chain. mtDNA mutations alone cannot explain the characteristic reduced penetrance, gender bias and secondary phenotypes of LHON. Recent work on LHON has often, unsuccessfully, focused on the identification of a nuclear-encoded modifying gene which would explain these characteristics. Thus, the aims of this PhD were, i) to improve our estimates of disease penetrance and investigate other potential disease modifiers, ii) to use LHON patient cell lines to investigate the effect ofmtDNAmutations on cellular processes whichmay contribute to LHONand iii) to evaluate retinal degeneration in a mtDNAmutation animal model. By investigating these key components of LHON we hope to improve our understanding of the disease process. Using a large familial cohort, we were able to update and improve current LHON penetrance estimates, with our analysis indicating that the penetrance in females is much higher than previous estimates. In addition, we were able to show that LHON cases have differential genetic variants and methylation patterns, identifying ~45nDNA modifier genes that may explain the variable penetrance and gender bias in LHON. Primary LHON fibroblasts were further characterised across a range of biochemical mechanisms. Analysis of an mtDNA mutation mouse has improved our understanding of the effect of mtDNA mutation on RGC loss. Work in this PhD has identified a technical framework that could be applied to other models with optic neuropathy.