IDH1 and Cowden syndrome 1: In conventional CS, about 50% of cases harbor somatic mutations in isocitrate dehydrogenase 1 (IDH1) and isocitrate dehydrogenase 2 (IDH2) mutations, the majority being IDH1 R132C/H and a smaller subset IDH2 R172 mutations (6), which are the same mutations seen in about 80% of patients with Ollier disease and Maffucci syndrome (6–8).