Skeletal dysplasia due to Smad4 deficiency resembles other skeletal dysplasias resulting from mutations in polarity pathways, such as the Ror2/Wnt5a PCP pathway with Robinow syndrome and brachydactyly B2 (Afzal et al., 2000; Wang et al., 2010). Here, SMAD4 is linked to skeletal dysplasia.