EN1 and Parkinson disease: Previous works have shown that OF1-En1+/− mice exhibit loss of nigrostriatal dopaminergic neurons (Sonnier et al., 2007; Nordström et al., 2015) while C57-En1+/− mice lack this PD-like phenotype and require homozygous deletion of En2 (En2+/−) to develop a similar neurodegeneration (Sgadò et al., 2006).