Cantú syndrome (CS, OMIM 239850), first described in 1982, is a rare multisystem disorder caused by gain-of-function (GOF) mutations in subunits of ATP-sensitive potassium (KATP) channels, specifically the pore-forming Kir6.1 (KCNJ8) and regulatory SUR2 (ABCC9) subunits (1–4). The gene discussed is KCNJ8; the disease is Cowden syndrome 1.