The 16.22 Mb region of 8p23.3p22 contains 81 protein-coding genes, including a large defensin cluster (23) and a haploinsufficiency gene, GATA4. GATA4 is related to atrial septal defect 2, atrioventricular septal defect 4, tetralogy of Fallot, and ventricular septal defect 1 in an autosomal dominant manner [OMIM: 600576]. The gene discussed is GATA4; the disease is familial atrioventricular septal defect.