Amer2 (APC membrane recruitment 2; FAM123A) is a direct interaction partner of adenomatous polyposis coli (APC), related to the tumor suppressor Amer1/WTX. FAM123A interacts with APC via two domains that bind the Armadillo repeats of APC. These domains are conserved in the related proteins Amer1/WTX (Wilms tumor gene on the X-chromosome; FAM123B), which acts as a negative regulator of Wnt signaling, and Amer3 (FAM123C). Amer1 is mutated in Wilms tumors and in the inherited disease osteopathia striata congenita with cranial sclerosis. Amer2 negatively regulates Wnt signaling probably by interfering with β-catenin.