Leber's hereditary optic neuropathy (LHON) is the most frequent mitochondrial disease and was the first to be genetically defined by a point mutation in the mitochondrial DNA (mtDNA). A molecular diagnosis is reached in up to 95%, the vast majority of which are accounted for by three mutations within mitochondrial complex I (CI) subunit encoding genes in the mtDNA (mtLHON). Here, we resolve the enigma of LHON in the absence of pathogenic mtDNA mutations. We describe biallelic mutations in a nuclear encoded gene, DNAJC30, in 33 unsolved patients from 29 families and establish an autosomal recessive mode of inheritance for LHON (arLHON), which to date has been a prime example of a maternally inherited disorder. Remarkably, all hallmarks of mtLHON are recapitulated, including incomplete penetrance, male predominance, and significant idebenone responsivity. Moreover, by tracking protein turnover in patient-derived cell lines and a DNAJC30-knock-out cellular model, we measure reduced turnover of specific CI N-module subunits and a resultant impairment of CI function. This demonstrates DNAJC30 is to be a chaperone protein needed for the efficient exchange of CI subunits exposed to reactive oxygen species and integral to a mitochondrial CI repair mechanism, thereby providing the first example of a disease resulting from impaired exchange of assembled respiratory chain subunits.
GrantsHorizon2020 through ERA PerMed project PerMiM German BMBF Horizon2020 through the ERare project GENOMIT Italian Ministry of Health Deutsche Forschungsgemeinschaft (DFG) Cardio Pulmonary Institute (CPI) of the DFG National Institute for Health Research (NIHR) Oxford Biomedical Research Centre (BRC, Oxford, United Kingdom) Austrian Science Fund (FWF) German Federal Ministry of Education and Research (BMBF, Bonn, Germany)