Abstract
The tooth enamel development gene, enamelin (ENAM), showed evidence of positive selection during a genome-wide scan of human and primate DNA for signs of adaptive evolution. The current study examined the hypothesis that a single-nucleotide polymorphism (SNP) C14625T (rs7671281) in the ENAM gene identified in the genome-wide scan is associated with a change in enamel phenotype. African Americans were selected as the target population, as they have been reported to have a target SNP frequency of approximately 50%, whereas non-Africans are predicted to have a 96% SNP frequency. Digital radiographs and DNA samples from 244 teeth in 133 subjects were analysed, and enamel thickness was assessed in relation to SNP status, controlling for age, sex, tooth number and crown length. Crown length was found to increase with molar number, and females were found to have thicker enamel. Teeth with larger crowns also had thicker enamel, and older subjects had thinner enamel. Linear regression and generalized estimating equations were used to investigate the relationship between enamel thickness of the mandibular molars and ENAM SNP status; enamel in subjects with the derived allele was significantly thinner (P=0.040) when the results were controlled for sex, age, tooth number and crown length. The derived allele demonstrated a recessive effect on the phenotype. The data indicate that thinner dental enamel is associated with the derived ENAM genotype. This is the first direct evidence of a dental gene implicated in human adaptive evolution as having a phenotypic effect on an oral structure.
Highlights
Teeth are crucial for animal survival, and the preservation of their function is important in natural selection.[1]
The current study examined the hypothesis that a single-nucleotide polymorphism (SNP) C14625T in the ENAM gene identified in the genome-wide scan is associated with a change in enamel phenotype
Evidence of positive selection has been found in ENAM along the lineage leading to chimpanzees,[6] and thicker enamel is the ancestral condition of the great apes.[4]
Summary
Teeth are crucial for animal survival, and the preservation of their function is important in natural selection.[1]. As the diet of early humans changed from harder objects to meat and cooked foods, thinner enamel might have been advantageous in maintaining sharp enamel crests, which are better for shearing, versus thicker enamel, which promotes resistance to grinding,[9] or perhaps there was less selective pressure to maintain thicker enamel
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