PPARGC1A and Parkinson disease: The following subsections emphasize the relevance of mitochondrial dysfunction in the pathomechanism of degenerative CNS disorders through a detailed overview on the involvement of impaired OXPHOS and mitochondrial bioenergetics in Parkinson's disease, Huntington's disease, and mitochondrial encephalopathies, with special focus on the involvement and therapeutic relevance of PGC-1α.