IRF6 and popliteal pterygium syndrome: IRF6 mutations, in addition to causing Van der Woude syndrome, can cause popliteal pterygium syndrome, an autosomal dominant disorder characterized by orofacial anomalies including lower lip pits, cleft lip and/or palate, syngnathia, syndactyly, webbing of the lower limbs, and genital abnormalities [87].