HTRA2 and Parkinson disease: At the same time, the discovery of various genes, such as α-synuclein [4], parkin [5], DJ-1 [6], PTEN-induced kinase 1 (PINK-1) [7], HtrA2/Omi gene [8], and leucine-rich repeat kinase 2 (LRRK2) [9] linked to familial forms of PD provides vital hints for the understanding the pathogenesis of the disease.