PRKN and Parkinson disease: In brief, implications of the involvement of mitochondrial dysfunction in PD stem from findings that (1) substantia nigra neurons from PD patients exhibit accumulations of mtDNA deletions; (2) significant deficits occur in the activity of mitochondrial respiratory chain complex I; and mutants of PINK-1, DJ-1, and Parkin, which are involved in mitochondrial functioning [70, 71], are found in PD.