Six families with van der Woude and/or popliteal pterygium syndrome: all with a mutation in the IRF6 gene.

V an der Woude syndrome (VWS, OMIM #119300) is a dominantly inherited developmental disorder characterised by pits and/or sinuses of the lower lip, cleft lip with or without cleft palate (CL/P), isolated cleft palate (CP), bifid uvula (BU), and hypodontia (H). Cleft lip deformity is established during the first 6 weeks of life due to failure of fusion of maxillary and medial nasal processes or to incomplete mesodermal ingrowth into the processes. Palatal clefts result from failure of fusion of the palatal shelves that normally change from a vertical to horizontal position and fuse during the sixth to ninth weeks of gestation. The severity of VWS varies widely, even within families. About 25% of individuals with the syndrome have minimal findings, such as absent teeth or trivial indentations in the lower lips. Clefting of the lip or palate is present in ,50% of cases. Lip pits and/or sinuses are the cardinal features of this syndrome, present in 70–80% of VWS patients. They are often associated with accessory salivary glands that empty into the pits, sometimes leading to embarrassing visible discharge. 5 Another syndrome closely mimicking VWS is popliteal pterygium syndrome (PPS, OMIM #119500). It combines VWS signs and symptoms with popliteal and oral webs, unusual nails, syndactyly, ankyloblepharon, and genital anomalies (fig 1). VWS is the most common cleft syndrome, affecting 1 in 35 000–100 000 people (,1/70 000). About 1–2% of patients with cleft lip or palate have VWS. The VWS pedigrees suggest an autosomal dominant inheritance pattern, yet, in 30–50% of cases, mutation may rise de novo. Penetrance is estimated to be about 75%, but is actually closer to 100% when supposedly unaffected carriers are closely examined for minor expressions of the syndrome. 4 PPS is a rarer malformation, with an incidence of 1/300 000. Most reported cases of VWS have been linked to chromosome 1q32-q41 (VWS1), but a second VWS locus (VWS2) has been mapped to 1p34. Recently, the interferon regulatory factor-6 (IRF6) gene, localised to the VWS1 locus on chromosome band 1q32.2, was shown to harbour mutations in patients with Van der Woude and/or popliteal pterygium syndrome. IRF6 belongs to a family of nine transcription factors that share a highly conserved helix turn helix DNA binding domain and a less conserved protein binding domain called SMIR. 16 In the only report so far on mutations in the IRF6 gene in VWS and PPS patients, not all families harboured an alteration in IRF6. Thus, analysis of novel families, with or without PPS, is interesting in order to determine the prevalence of IRF6 as a disease causative gene and to identify additional mutations responsible for VWS with or without PPS. In this study, we screened six VWS and PPS families followed at the Centre Labiopalatin for mutations. A novel mutation was identified in IRF6 for all the cases. MATERIALS AND METHODS Family assessment Patients diagnosed as VWS were recalled from the registries of the Cleft Lip and Palate Centre and the Centre for Human Genetics. All the families had members with clefts of the lip and/or palate, lip pits, or bifid uvula, and were thus considered VWS patients. In family VWS5, individuals IV:1 and IV:3 had, in addition to VWS features, oral synechiae and syndactyly, which are signs of PPS. The clinical data for each individual are shown in figure 2. Each participant gave informed consent prior to his/her participation in the study, as approved by the ethics committee of the medical faculty at the Université catholique de Louvain. The status of the unaffected individuals has been ascertained in order to identify all the microforms of VWS, especially small lip sinuses and hypodontia. For genomic DNA extraction, venous blood samples were drawn for all participants other than VWS11-II:1, for whom a buccal cell sample was obtained. DNA was extracted by isopropanol precipitation or, from the buffy coats, using QIAamp DNA Blood Mini Kit (Qiagen, Westburg, Leusden, The Netherlands). A second blood sample was obtained from some individuals for lymphocytic transformation with Epstein-Barr virus.