The same as for Van der Woude syndrome, mutation in the interferon regulatory factor 6 gene is presumed to be responsible for the disorder.6) Bartsocas and Papas7) postulated that PPS can be inherited in an autosomal dominant and an autosomal recessive manner; autosomal dominant PPS is more common and it shows variable penetrance, but autosomal recessive PPS occurs in patients who are born to unaffected parents and it is associated with more severe anomalies and mental retardation. This evidence concerns the gene IRF6 and popliteal pterygium syndrome.