Craniofacial Morphology in Human Genetics

Abstract

Hereditary studies of dental characteristics (size and shape) in humans have demonstrated that strong genetic factors affect the variance of many dental traits. In addition, the characteristics of the dental morphology have acted as an indicator of biological distance between human populations. Recent advances in molecular biology have revealed major molecules involved in the development of teeth. However, genetic determinants of common dental characteristics have been less understood. It was previously reported that a variant of EDAR is associated with shovel-shaped incisors; this is an example of where a genetic determinant of common dental characteristics has been identified. PAX9 is an important transcription factor for developing teeth. Dysfunctional mutations in PAX9 cause selective tooth agenesis in humans. The purpose of this study was to examine whether common variants of PAX9 participate in common dental characteristics in East Asian populations. The study subjects were Japanese and Korean adults. The single nucleotide polymorphisms (SNP) in PAX9 were genotyped with the TaqMan method. The mesiodistal and buccolingual diameters were measured as metric dental traits. As non-metric traits, the shovel grade, double shovel grade, tuberculum dentale in upper incisors and canines, Carabelli trait in upper molars, cusp numbers of the upper and lower molars, and groove pattern of the lower molars were examined. This facilitated the association between genotypes and dental characteristics to be determined. The SNP was significantly associated with several tooth crown diameters and the tuberculum dentale in the upper incisors. It is concluded that a common variant of PAX9 contributes to crown size and shape variation in human permanent teeth.