Supplementary MaterialsSupplementary material 1 (DOC 631 kb) 401_2016_1625_MOESM1_ESM. of retinal ganglion cells (RGCs) within the inner retina but, rather strikingly, the smaller calibre RGCs that constitute the papillomacular bundle are particularly vulnerable, whereas melanopsin-containing RGCs are relatively spared. Although the majority of patients with LHON and DOA will present with isolated optic nerve involvement, some individuals will also develop additional neurological complications pointing towards a greater vulnerability of the central nervous system (CNS) in susceptible mutation carriers. These so-called plus phenotypes are mechanistically important as they put the loss of RGCs within the broader perspective of neuronal loss and mitochondrial dysfunction, highlighting common pathways that could be modulated to halt progressive neurodegeneration in other related CNS disorders. The management of patients with mitochondrial optic neuropathies still remains largely supportive, but the development of effective disease-modifying treatments is now within tantalising reach helped by major advances in drug discovery and delivery, and targeted genetic manipulation. Electronic supplementary material The online version of this article (doi:10.1007/s00401-016-1625-2) contains supplementary material, which is available to authorized users. mutation. There is prominent temporal optic disc pallor and marked RNFL thinning except in the nasal quadrant, which is relatively spared. The disc area analysis reveals small optic discs in both eyes. The bottom panel shows pronounced macular ganglion cell layer thinning in all sectors. Please refer to the Supplementary Appendix for a more detailed explanation of the OCT measurements and their anatomical correlates The majority (60C70?%) of patients with DOA harbour pathogenic mutations in the nuclear gene that encodes for a mitochondrial inner membrane protein with multifunctional properties [4, 47]. Over 250 mutations have been reported and these can be grouped into two major categories depending on whether they are predicted to cause disease due to haploinsufficiency (deletions, insertions, PU-H71 irreversible inhibition splice site and nonsense mutations) or a possible dominant-negative mechanism (missense mutations) [50, 53]. More recently, heterozygous mutations in a number of nuclear genes have been identified in patients with DOA, including dominant mutations in families segregating optic atrophy and early onset cataracts . The OPA3 protein is a mitochondrial outer membrane protein with pro-fission properties PU-H71 irreversible inhibition and the loss of RGCs has been linked to disturbed mitochondrial dynamics . Interestingly, DRP1 is also a pro-fission cytosolic protein that is recruited to the mitochondrial outer membrane, and both and encode for mitochondrial AAA proteases that operate PU-H71 irreversible inhibition as oligomeric complexes to regulate the post-translational processing of OPA1 [39, 78, 135]. Rather strikingly, with the exception of gene, c.1334G? A (p.Arg455His), has been consistently associated with sensorineural deafness in a number of families [6, 144]. The clinical manifestations observed in disease have now expanded further to include chronic progressive external ophthalmoplegia (CPEO) and other extraocular features such as ataxia, myopathy and peripheral neuropathy [7, 13, 65]. In a large multicentre study of 104 patients with DOA plus phenotypes from 45 independent families, up to 20?% of familial carriers developed multisystemic neuromuscular complications and the risk was significantly increased among those harbouring missense mutations, consistent with a putative dominant-negative effect . Rather unexpectedly, analysis of muscle biopsies obtained from this group of patients revealed multiple mtDNA deletions and the presence of high levels of cytochrome oxidase (COX)-deficient muscle fibres, some of which had marked mitochondrial proliferation in the form of ragged-red fibres [125, 144]. The accumulation of mtDNA deletions is a fascinating observation that could be due to the accelerated clonal expansion COL12A1 of these somatic mutations to sufficiently high levels PU-H71 irreversible inhibition to trigger a biochemical COX defect [102, 146]. CPEO is a classical manifestation of mitochondrial disease and in keeping PU-H71 irreversible inhibition with the propensity of extraocular muscles to accumulate somatic mtDNA mutations at a.