Genetics of human body size and shape: Body proportions and indices

Background: The study of the genetic component in morphological variables such as body height and weight, head and chest circumference, etc. has a rather long history. However, only a few studies investigated body proportions and configuration. Aim: The major aim of the present study was to evaluate the extent of the possible genetic effects on the inter-individual variation of a number of body configuration indices amenable to clear functional interpretation. Subjects and methods: Two ethnically different pedigree samples were used in the study: (1) Turkmenians (805 individuals) from Central Asia, and (2) Chuvasha (732 individuals) from the Volga riverside, Russian Federation. To achieve the aim of the present study we proposed three new indices, which were subjected to a statistical-genetic analysis using modified version of 'FISHER' software. The proposed indices were: (1) an integral index of torso volume (IND#1), an index reflecting a predisposition of body proportions to maintain a balance in a vertical position (IND#2), and an index of skeletal extremities volume (IND#3). Additionally, the first two principal factors (PF1 and PF2) obtained on 19 measurements of body length and breadth were subjected to genetic analysis. Variance decomposition analysis that simultaneously assess the contribution of gender, age, additive genetic effects and effects of environment shared by the nuclear family members, was applied to fit variation of the above three indices, and PF1 and PF2. Results: The raw familial correlation of all study traits and in both samples showed: (1) all marital correlations did not differ significantly from zero; (2) parent-offspring and sibling correlations were all positive and statistically significant. The parameter estimates obtained in variance analyses showed that from 40% to 75% of inter-individual variation of the studied traits (adjusted for age and sex) were attributable to genetic effects. For PF1 and PF2 in both samples, and for IND#2 (in Chuvasha pedigrees), significant common sib environmental effects were also detectable. Conclusion: Genetic factors substantially influence inter-individual differences in body shape and configuration in two studied samples. However, further studies are needed to clarify the extent of pleiotropy and epigenetic effects on various facets of the human physique.