Interaction Between IRF6 and TGFA Genes Contribute to Isolated Clefting

Objectives: Previous evidence from hypodontia studies suggested that IRF6 and TGFA may interact. Since hypodontia is commonly found in individuals with cleft lip/palate (CL/P), we used two large cohorts to evaluate if IRF6 and TGFA interaction contributes to CL/P.

Methods: Markers located within and flanking the IRF6 and TGFA genes were tested using Taqman or SYBR green chemistries for case-control analyses in 1,000 Brazilian individuals (500 cases/500 controls) and for transmission distortion tests in an additional 304 case-parent triads from ECLAMC. We looked for evidence of gene-gene interaction between IRF6 and TGFA by testing if markers associated with CL/P were overtransmitted together. Finally, Tgfa expression was analyzed by immunohistochemistry in Irf6 knockout mice at E14.5.

Results: IRF6 showed association with CL/P in both Brazilian (p=0.00001) and ECLAMC populations (p=0.0002). In addition in the Brazilian cohort, IRF6 was associated with complete cleft palate only with impaction of permanent teeth (p=0.00001). TGFA was also associated with CL/P in Brazilians (p=0.00001), but the results were just borderline in the ECLAMC (p=0.097).

Statistical evidence of interaction between IRF6 and TGFA was found for the Brazilian and ECLAMC sample sets (p=0.013, p=0.046, respectively). Attributable fraction calculations suggested that such interaction explains 1% of CL/P in Brazilians and 4.6% in the ECLAMC. In Irf6 knockout mice, Tgfa expression appeared to be reduced in the palatal epithelium when compared to wild-type littermates.

Conclusions: We provide further evidence that IRF6 and TGFA contribute to CL/P and to subsets of CL/P cases with specific associated dental anomalies. Moreover, IRF6-TGFA interaction appears to contribute to as much as 1% to 4.6% of CL/P cases. The Irf6-knockout model further support the evidence of IRF6-TGFA interaction we found in humans. This work is supported by NIH grant R21 De 16718 and Brazilian grants

CNPq 308885/2006-0 and 401467/2004-0, FAPERJ E-26/152.831/2006, and CAPES.