In previous work, we discovered that rare damaging variants in the MYH6 gene, which encodes α-MHC, the major MHC of the developing human ventricle and adult atrium, are present in 10% of patients with HLHS and are found throughout the head, neck, and tail domains of the α-MHC (18). The gene discussed is HLA-C; the disease is hypoplastic left heart syndrome.