ObjectiveOur goal was to identify the gene(s) associated with an early-onset form of Parkinson disease (PD) and the molecular defects associated with this mutation.MethodsWe combined whole-exome sequencing and functional genomics to identify the genes associated with early-onset PD. We used fluorescence microscopy, cell, and mitochondrial biology measurements to identify the molecular defects resulting from the identified mutation.ResultsHere, we report an association of a homozygous variant in CHCHD2, encoding coiled-coil-helix-coiled-coil-helix domain containing protein 2, a mitochondrial protein of unknown function, with an early-onset form of PD in a 26-year-old Caucasian woman. The CHCHD2 mutation in PD patient fibroblasts causes fragmentation of the mitochondrial reticular morphology and results in reduced oxidative phosphorylation at complex I and complex IV. Although patient cells could maintain a proton motive force, reactive oxygen species production was increased, which correlated with an increased metabolic rate.ConclusionsOur findings implicate CHCHD2 in the pathogenesis of recessive early-onset PD, expanding the repertoire of mitochondrial proteins that play a direct role in this disease.