Interferon regulatory factor 6 (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. Most IRFs regulate the expression of interferon-alpha and -beta after viral infection, but the function of IRF6 is unknown. The gene encoding IRF6 is located in the critical region for the Van der Woude syndrome (VWS; OMIM 119300) locus at chromosome 1q32-q41 (refs 2,3). The disorder is an autosomal dominant form of cleft lip and palate with lip pits, and is the most common syndromic form of cleft lip or palate. Popliteal pterygium syndrome (PPS; OMIM 119500) is a disorder with a similar orofacial phenotype that also includes skin and genital anomalies. Phenotypic overlap and linkage data suggest that these two disorders are allelic. We found a nonsense mutation in IRF6 in the affected twin of a pair of monozygotic twins who were discordant for VWS. Subsequently, we identified mutations in IRF6 in 45 additional unrelated families affected with VWS and distinct mutations in 13 families affected with PPS. Expression analyses showed high levels of Irf6 mRNA along the medial edge of the fusing palate, tooth buds, hair follicles, genitalia and skin. Our observations demonstrate that haploinsufficiency of IRF6 disrupts orofacial development and are consistent with dominant-negative mutations disturbing development of the skin and genitalia.

DNA-sequence variants associated with IRF6 are major contributors to cleft lip, with or without cleft palate. The contribution of variants in single genes to cleft lip or palate is an important consideration in genetic counseling.

Nonsyndromic cleft lip with or without cleft palate (CL/P) and nonsyndromic cleft palate only (CPO) are common congenital anomalies with significant medical, psychological, social, and economic ramifications. Both CL/P and CPO are examples of complex genetic traits. There exists sufficient evidence to hypothesize that disease loci for CL/P and CPO can be identified by a candidate-gene linkage-disequilibrium (LD) strategy. Candidate genes for clefting, including TGFA, BCL3, DLX2, MSX1, and TGFB3, were screened for LD with either CL/P or CPO in a predominantly Caucasian population, with both case-control- and nuclear-family-based approaches. Previously reported LD for TGFA with both CL/P and CPO could not be confirmed, except in CL/P patients with a positive family history. Also, in contrast to previous studies, no LD was found between BCL3 and either CL/P or CPO. Significant LD was found between CL/P and both MSX1 and TGFB3 and between CPO and MSX1, suggesting that these genes are involved in the pathogenesis of clefting. In addition, a mutation search in the genes DLX2, MSX1, and TGFB3 was performed in 69 CPO patients and in a subset of the CL/P patients. No common mutations were found in the coding regions of these genes; however, several rare variants of MSX1 and TGFB3 were found that may alter the latters' normal function. These results form the basis for future research, including (a) mutation searches in the MSX1 and TGFB3 genes in Caucasian CL/P patients and (b) extension of the search for MSX1 mutations in CPO patients to the noncoding regions.

Nonsyndromic cleft lip and palate (NS CLP) is a complex birth defect resulting from a combination of genetic and environmental factors. Several members of the FGF and FGFR families are expressed during craniofacial development and can rarely harbor mutations that result in human clefting syndromes. We hypothesized that disruptions in this pathway might also contribute to NS CLP. We sequenced the coding regions and performed association testing on 12 genes (FGFR1, FGFR2, FGFR3, FGF2, FGF3, FGF4, FGF7, FGF8, FGF9, FGF10, FGF18, and NUDT6) and used protein structure analyses to predict the function of amino acid variants. Seven likely disease-causing mutations were identified, including: one nonsense mutation (R609X) in FGFR1, a de novo missense mutation (D73H) in FGF8, and other missense variants in FGFR1, FGFR2, and FGFR3. Structural analysis of FGFR1, FGFR2, and FGF8 variants suggests that these mutations would impair the function of the proteins, albeit through different mechanisms. Genotyping of SNPs in the genes found associations between NS CLP and SNPs in FGF3, FGF7, FGF10, FGF18, and FGFR1. The data suggest that the FGF signaling pathway may contribute to as much as 3-5% of NS CLP and will be a consideration in the clinical management of CLP.fibroblast growth factor ͉ fibroblast growth factor receptor ͉ single-nucleotide polymorphism ͉ cleft palate

We report here the identification of a new human homeobox gene, PITX3, and its involvement in anterior segment mesenchymal dysgenesis (ASMD) and congenital cataracts in humans. The PITX3 gene is the human homologue of the mouse Pitx3 gene and is a member of the RIEG/PITX homeobox gene family. The protein encoded by PITX3 shows 99% amino-acid identity to the mouse protein, with 100% identity in the homeodomain and approximately 70% overall identity to other members of this family. We mapped the human PITX3 gene to 10q25 using a radiation-hybrid panel. A collection of 80 DNA samples from individuals with various eye anomalies was screened for mutations in the PITX3 gene. We identified two mutations in independent patients. A 17-bp insertion in the 3'-end of the coding sequence, resulting in a frame shift, occurred in a patient with ASMD and cataracts, and a G-->A substitution, changing a codon for serine into a codon for asparagine, in the 5'-end of the gene occurred in a patient with congenital cataracts. Both mutations cosegregate with the disease phenotype in families, and neither were found in up to 300 control individuals studied. Further expression analysis of Pitx3 in the mouse supports a unique role in early ocular development, with later expression extending to the midbrain, tongue, incisors, sternum, vertebrae and limbs. These data strongly suggest a role for PITX3 in ASMD and cataracts and provide new evidence of the contribution of the RIEG/PITX gene family to the developmental program underpinning normal eye formation.