PRMT2 and Down syndrome: Ms4Yah mice monosomic for the Prmt2–Cstb region on Mmu10 were crossed with the Down syndrome mouse model Tc1, trisomic for ∼81% of the Hsa21 genes, to test the role of the 47 mouse genes with homologues in human present in the Prmt2–Cstb region in the phenotypes observed in Tc1 mice.