Affects 1 in 400–1000 live births; caused by mutations in PKD1 (Chr16) or PKD2 (Chr4). Renal manifestations include haematuria, hypertension, renal stones, urinary tract infection and progressive renal failure. Subarachnoid haemorrhage may be a complication of ruptured cerebral aneurysms. The gene discussed is PKD1; the disease is brain aneurysm.