NKX2-5 and atrial septal defect: The subsequent histological analysis revealed the presence of compound ASD/VSD in the K51R-Tg/Nkx2.5+/− mouse hearts (compare E′ with B′, C′ and D′) in 10 out of 11 demised K51R-Tg/Nkx2.5+/− mice examined, and a single ASD in 1 mouse.