Leber's hereditary optic neuropathy (LHON) is the most common mitochondrial disease and in most cases is caused by mutations in mitochondrial DNA-encoded (mtDNA-encoded) respiratory complex I subunit ND1, ND4, or ND6. In this issue of the JCI, Stenton et al. describe biallelic mutations in a nuclear DNA-encoded gene, DNAJC30, establishing recessively inherited LHON (arLHON). Functional studies suggest that DNAJC30 is a protein chaperone required for exchange of damaged complex I subunits. Hallmark mtDNA LHON features were also found in arLHON, including incomplete penetrance, male predominance, and positive response to idebenone therapy. These results extend complex I-deficient phenotypes to include recessively inherited optic neuropathy, with important clinical implications for genetic counseling and therapeutic considerations.