The locus harboring COL4A1/A2 is a highly replicated susceptibility locus for coronary- and peripheral artery disease, respectively8,9, and the relevance of the BM in artery biology is evident from rare familial syndromes caused by missense mutations in COL4A1. Aneurysms of carotid and cerebral arteries are common features of these syndromes, collectively termed hereditary angiopathy with nephropathy, aneurysms, and muscle cramps (HANAC syndrome)10,11, underlining the importance of COL4A1/A2 integrity in the artery wall. The gene discussed is COL4A1; the disease is autosomal dominant familial hematuria-retinal arteriolar tortuosity-contractures syndrome.