The lack of one Foxa2 allele affected mostly the SNc DA neurons in an asymmetric manner, a key feature of PD (Balestrino and Schapira, 2020; Blesa et al., 2022), in ~30% of these aging Foxa2+/− mice (Kittappa et al., 2007). The gene discussed is FOXA2; the disease is Parkinson disease.