IRF6 and van der Woude syndrome: The spectrum of clinical variability of VWS has recently been expanded by the demonstration that mutations in IRF6 are also causative of the Popliteal Pterygium Syndrome (PPS; OMIM 119500), an allelic, autosomal dominant disorder that presents, besides the facial anomalies typical of VWS, bilateral popliteal webs, syndactyly, and genital anomalies [17].