Whereas AS is caused by defects in the E3 ubiquitin ligase UBE3A/E6AP gene located at chromosome 15q11.2 [6, 7], CS was recently found to arise from mutations in the gene encoding the pH-regulating solute carrier (Na+, K+)/H+ exchanger NHE6/SLC9A6 located at chromosome Xq26.3 [2, 3, 8, 9]. The gene discussed is UBE3A; the disease is Cowden syndrome 1.