HTRA2 and Parkinson disease: Mutations or polymorphisms in mitochondrial DNA or nuclear genes (α-synuclein, tau, parkin, C-terminal hydrolase-L1, ubiquitin DJ-1, leucine-rich-repeat kinase 2, PTEN (phosphatase and tensin homologue)-induced kinase 1, nuclear receptor NURR1, and HTRA2) have been identified as possible risk factors for developing PD, where nuclear genes α-synuclein, DJ-1, parkin, phosphatase and tensin homologue-induced kinase 1, leucine-rich-repeat kinase 2, and HTRA2 involve mitochondria [34].