ENSG00000251605 and Parkinson disease: A low-grade deficiency in mitochondrial electron transport chain (ETC) Complex I (NADH dehydrogenase) activity has been found not only in PD brain, but also other non-neuronal tissues throughout the body (Parker et al., 1989, 2008; Schapira et al., 1989; Krige et al., 1992; Yoshino et al., 1992; Barroso et al., 1993; Mann et al., 1994; Taylor et al., 1994; Haas et al., 1995; Penn et al., 1995; Blandini et al., 1998; Keeney et al., 2006), suggesting a systemic mitochondrial respiration deficit associated with PD.