Mitochondrial dysfunction has been clearly established as a hallmark of genetic PD, since proteins encoded by the autosomal inherited PD genes—like parkin (PARK2), PTEN-induced kinase 1 (PINK1; PARK6), deglycase DJ-1 (PARK7), high-temperature requirement serine protease A2 (Omi/HTRA2; PARK13), coiled-coil-helix-coiled-coil-helix domain containing 2 (CHCHD2; PARK22), and vacuolar protein sorting ortholog 35 (VPS35; PARK17)—are located in the mitochondria and/or deeply involved in several mitochondrial functions, including the process of mitophagy. This evidence concerns the gene HTRA2 and Parkinson disease.