IRF6 and popliteal pterygium syndrome: Rare heterozygous variants in IRF6 (interferon regulatoryfactor-6) gene cause van der Woude syndrome 1 (VWS1) or Popliteal Pterygiumsyndrome, two forms of syndromic cleft lip/palate (CLP) that present with avariety of congenital malformations due to impairment ectodermal homeostasis.These malformations include, in addition to CLP, lip pits, pterygia, andintraoral and eyelid fibrous bands.