Of the nuclear genes, mutations in SNCA, PARK2 (also known and hereafter referred to as parkin), PINK1 (PTEN induced putative kinase 1), PARK7 (also known and hereafter referred to as DJ-1), LRRK2 (leucine-rich repeat kinase 2) and HTRA2 (high temperature requirement A2) provide direct or indirect evidence for a major role of mitochondrial dysfunction in PD. This evidence concerns the gene HTRA2 and Parkinson disease.