For cerebral neurons, we observed downregulation of known HD-associated neuronal genes, such as Drd1, Drd2, Penk, Ppp1r1b, Pde10a, Arpp21, and Pcp4, all commonly reported to be downregulated in both human HD patients and various HD mouse models [36–38] (Fig. 3C). The gene discussed is ARPP21; the disease is Huntington disease.