AMER1 and Cowden syndrome 1: OS-CS has been classically considered an autosomal dominant condition with high penetrance and variable intra- and interfamilial expressivity [4,9,12,15-17,21,43] until the recent identification of mutated WTX (Wilms Tumor in the X; also called FAM123B and AMER1) within proximal Xq11.2 in affected families [8].