Common genetic and environmental factors among craniofacial traits in Belgian nuclear families: comparing skeletal and soft-tissue related phenotypes.

The major objective of this study was to determine the possible effects of common genetic and environmental factors among 18 craniofacial anthropometric traits, with special attention to the differences between skeletal and soft-tissue related phenotypes. The studied sample consisted of 122 nuclear families living in Brussels and included 251 males and 258 females aged from 13 to 72 years. Univariate and bivariate quantitative genetic analyses were performed using a variance components procedure implemented in SOLAR software. All phenotypes were significantly influenced by additive genetic factors with heritability estimates ranging from 0.46 (nose height) to 0.72 (external biocular breadth). Sex, age and their interactions explained 7-46% of the total phenotypic variance of the traits. Bivariate analysis revealed that several traits share a common genetic and/or environmental basis while other traits show genetic and environmental independence from one another. More and greater genetic and environmental correlations were observed among skeletal phenotypes, than among soft-tissue traits and between both categories. Apart from the tissue composition, other characteristics of the craniofacial morphology such as the orientation (e.g. heights, breadths) have shown to be important factors in determining pleiotropy and common environmental effects between some pairs of traits. In conclusion, the results confirm that overall head configuration is largely determined by additive genetic effects, and that common genetic and environmental factors affecting craniofacial size and shape are stronger for the skeletal traits than for the soft-tissue traits.