SNCA and Parkinson disease: As such, the discovery that mutations in the mitochondrial intermembrane space protein CHCHD2 (coiled-coil–helix–coiled-coil–helix domain–containing 2) cause an autosomal dominant form of late-onset PD that closely resembles sporadic PD (28)—including widespread α-synuclein deposition (29)—proves that mitochondrial dysfunction can cause autosomal dominant PD, and strongly implicates it as a causal factor in at least a subset of idiopathic PD.