Multiple pterygium syndromes comprise a group of multiple congenital anomaly disorders characterized by webbing (pterygia) of the neck, elbows, and/or knees and joint contractures (arthrogryposis) (Morgan et al., 2006). The multiple pterygium syndromes are phenotypically and genetically heterogeneous but are traditionally divided into prenatally lethal (253290) and nonlethal (Escobar) types.

Most commonly, IRF6-related disorders span a spectrum from isolated cleft lip and palate and Van der Woude syndrome (VWS) at the mild end to popliteal pterygium syndrome (PPS) at the more severe end. In rare instances, IRF6 pathogenic variants have also been reported in individuals with nonsyndromic orofacial cleft (18/3,811; 0.47%) and in individuals with spina bifida (2/192). Individuals with VWS show one or more of the following anomalies: Congenital, usually bilateral, paramedian lower-lip fistulae (pits) or sometimes small mounds with a sinus tract leading from a mucous gland of the lip. Cleft lip (CL). Cleft palate (CP). Note: Cleft lip with or without cleft palate (CL±P) is observed about twice as often as CP only. Submucous cleft palate (SMCP). The PPS phenotype includes the following: CL±P. Fistulae of the lower lip. Webbing of the skin extending from the ischial tuberosities to the heels. In males: bifid scrotum and cryptorchidism. In females: hypoplasia of the labia majora. Syndactyly of fingers and/or toes. Anomalies of the skin around the nails. A characteristic pyramidal fold of skin overlying the nail of the hallux (almost pathognomonic). In some nonclassic forms of PPS: filiform synechiae connecting the upper and lower jaws (syngnathia) or the upper and lower eyelids (ankyloblepharon). Other musculoskeletal anomalies may include spina bifida occulta, talipes equinovarus, digital reduction, bifid ribs, and short sternum. In VWS, PPS, IRF6-related neural tube defect, and IRF6-related orofacial cleft, growth and intelligence are typical.