The molecular basis of CS is now recognized to be gain of function (GOF) mutations in the ABCC9 and KCNJ8 genes, which encode the regulatory sulfonylurea receptor SUR2 (ABCC9) and pore-forming Kir6.1 (KCNJ8) subunits of ATP-sensitive K+ (KATP) channels (Harakalova et al., 2012; Cooper et al., 2014). Here, ABCC9 is linked to Cowden syndrome 1.