Adaptive Evolution in Enamelin and Human Tooth Enamel Thickness

Objectives: The tooth enamel development gene ENAM was found to show evidence of positive selection during a genome-wide scan of human and primate DNA. Studies have revealed that African Americans have thicker dental enamel in their deciduous teeth than European Americans. This study examines the hypothesis that the single nucleotide polymorphism (SNP) common in the African American population is associated with the enamel phenotype. Methods: Four bitewing digital radiographs and cheek swab DNA samples will be collected from 220 African-American subjects. From obtained radiographs, molar enamel thickness was measured as a function of tooth height and area. The DNA samples were amplified and sequenced for the SNP region of the ENAM gene. Results: DNA samples from 117 subjects have been taken at this point with accompanying enamel measurements, successfully isolating DNA from 97% of those subjects. The sequencing took place in the Genome Sciences Department at the University of Washington. With 45 samples completed, linear regression analysis found a trend of association between enamel thickness and SNP status; however, it was not statistically significant (P = 0.07). Conclusion: Enamel thickness may be associated with the ENAM gene polymorphism, and further data collection should provide a more definitive answer as we approach the target sample size. This is exciting pilot data addressing for the first time the role of a dental gene in adaptive evolution of the human species. This work is supported by an NSF-DIG, NIH T32 RR023256, and the University of Washington Hack Estate.