PRKN and Parkinson disease: On pathological examination, patients with PD show loss of dopaminergic neurons in the pars compacta of the substantia nigra.12,13 Mitochondrial dysfunction is thought to be the main cause of neuronal death in PD, because many of the causative genes of familial PD discovered so far encode proteins involved in mitochondrial maintenance, such as PINK1 and Parkin.14–16 However, the mechanism leading to the death of dopaminergic neurons remains to be elucidated.