On the other hand, the activation of the canonical Wnt/β-catenin pathway is well established in ACPs, which have been linked with the activating mutations of the b-catenin encoding gene CTNNB1 and, subsequently, the Wnt/β-catenin pathway activation, which was first described by Sekine et al. in 2002 [219]. The gene discussed is CTNNB1; the disease is acrocephalopolysyndactyly.