Pterygium syndrome, also known as popliteal pterygium syndrome, is a rare genetic disorder caused by a mutation in the IRF6 gene. It can cause cleft palate or lip, skin meshes, genital abnormalities, webbed fingers or toes, and other physical problems. Van der Woude syndrome is a similar condition caused by a different mutation of the same gene. Both disorders can cause cleft lip or palate, hypodontia, and other symptoms. Pterygium syndrome occurs in about 1 in 300,000 births, while Van der Woude syndrome accounts for about 2% of cases involving cleft lip or palate.
Features of pterygium syndrome can vary between individuals but typically include cleft palate or lip, skin meshes covering the posterior knee joint, and genital abnormalities. Other possible features may include webbed fingers or toes, so-called lip pits, or unusual skin folds on the jaws, eyelids, or big toes. This rare disorder is sometimes called popliteal pterygium syndrome, or PPS, as well as faciogenitopopliteal syndrome. It is known to be caused by a mutation in the IRF6 gene. Van der Woude syndrome is a closely related condition that results from a different mutation of the IRF6 gene, with some of the same symptoms as PPS.
A common feature of pterygium syndrome is some version of a cleft lip or palate. The lip malformation might cause dimples or depressions in the middle of the lower lip or unusual areas of skin on part of the individual’s lower lip. An individual’s palate, also known as the palate, may contain an abnormal opening. Some individuals with pterygium syndrome don’t have a typical number of teeth, a condition called hypodontia. All of these physical problems can cause difficulties in speech development.
Popliteal pterygium syndrome gets its name from the common involvement of the popliteal area behind the knee. Individuals with this disorder generally have webbed skin growing at the back of the knee and possibly extending to the person’s heel, making it difficult to walk or crawl without surgical removal of the cobwebs. This skin texture can also occur on the large toenails, and in some cases there is also foreign tissue partially connecting the jaws or lower and upper eyelids. Webbed or fused fingers and toes, known as syndactyly, are also common in people with pterygium syndrome.
Genital malformation frequently occurs in conjunction with pterygium syndrome. Female individuals may have very small outer lips. Males are likely to have a split scrotum or testicles that don’t descend normally, sometimes called cryptorchidism.
A similar congenital disorder is called Van der Woude syndrome. This disorder is also the result of mutations in the IRF6 gene. Individuals with Van der Woude syndrome also tend to have a pitted lower lip, cleft palate, cleft lip, or hypodontia.
Pterygium syndrome is extremely rare. Some estimates place the occurrence of this disorder at about 1 in 300,000 births. Van der Woude syndrome is slightly more common, accounting for about two percent of cases involving a cleft lip or cleft palate.
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