The En1+/− mouse displays progressive degeneration of nigral DA neurons (Nordström et al., 2015; Sonnier et al., 2007) and a specific decrease in mitochondrial complex activity (Alvarez-Fischer et al., 2011), similar to idiopathic PD (Mizuno et al., 1989; Schapira et al., 1990). Here, EN1 is linked to Parkinson disease.