Mutations in FGF Signaling Pathway Genes Contribute to Cleft Lip and Palate. B.M. Riley¹, M.A. Mansilla¹, L. Raffensperger¹, B. Maher², M.L. Marazita², M. Mohammadi³, J.C. Murray¹. 1) Dept Pediatrics, U of Iowa; 2) Ctr for Craniofacial and Dental Genetics, U of Pittsburgh; 3) Dept Pharmacology, NYU School of Medicine.
   Nonsyndromic cleft lip and palate (NSCLP) is a complex birth defect resulting from a combination of genetic and environmental factors. We hypothesize that members of the fibroblast growth factor (FGF) signaling pathway family contribute to NSCLP. Genotyping of SNPs in the FGF and FGFR candidate genes found significant P-value associations between NSCLP and FGF3, FGF7, FGF10, FGF18, and FGFR1 and the FGF3-FGF4 haplotype. Gene x gene interaction data supports interactions between members of the FGF family, such as FGF3/FGF18 and FGF10/FGF18, but also interactions with other NSCLP candidate genes. Medical resequencing of the coding regions of these genes in 184 NSCLP patients identified 7 novel mutations: FGFR1 M369I, E467K, R609X; FGFR2 R84S, D138N; FGFR3 V329I; and FGF8 D73H. Structural modeling of these proteins has elucidated possible functional roles for several of the mutations. Modeling of the D73H mutation indicates reduced biological activity due to disruption of FGF8 protein conformation and critical ligand-receptor binding interactions. These findings predict D73H to be a loss-of-function mutation. The E467K mutation may influence recruitment and phosphorylation of downstream signaling molecules due to its close proximity to Y463, one of FGFR1's autophosphorylation sites. Models of the V329I mutation predict that this mutation should lead to loss-of-function. Specifically, the mutation should destabilize the tertiary folding of the Ig domain 3, resulting in incomplete processing and retention of the mutated FGFR3 in intracellular compartments. These 7 point mutations may contribute to as much as 3-6% of isolated cleft lip and palate. Together with data from IRF6(12%); FOXE1, GLI2, MSX2, SKI, SATB2, and SPRY2(6%); and MSX1(2%), these genes can account for 23-26% of isolated cleft cases and have a significant impact on the clinical diagnosis and genetic counseling of CLP, in addition to providing further evidence that the FGF signaling pathway is important in lip and palate development.