Comparative study of fetal facial shape between Japanese and North American populations using micro-CT.

Population-level morphological differences in human cranio-skeletal morphology are reflective of a multitude of genetic, epigenetic, functional and environmental factors. While such differences have been described in postnatal and adult skeletons, how early they originate during cranio-skeletal ontogeny is unknown. Here we compare early human facial morphogenesis utilizing a collection of fetal specimens of Japanese (JP) and North American - European ancestry (NAP). Utilizing 3D micro-CT images and geometric morphometric analyses, we have identified subtle, yet significant differences in the morphology of the upper and midfacial regions in fetuses in the second trimester of gestation. Notably, the orbital rims and lateral areas of the zygomatic bones in the JP specimens have more prominent superior and inferior orbital rims, with a more prominent lateral project of the zygomatic bone, compared to the NAP. These data suggest that the cranioskeletal structures display early facial patterning unique to genealogically distinct populations. Since these specimens are derived from very early developmental stages, the impacts of functional factors are expected to be minor, while inherited genetic and epigenetic programming predominate in driving the observed morphological differences.