Family correlations of metacarpal bones--heritable (h2) and environmental (c2) components of total phenotypic...

The analysis of family data of 18 metacarpal morphometric dimensions (bone length -L, total diaphysis width-T and medullary canal width-M of the second, third and fourth metacarpals of both hands) has been performed on 956 randomly sampled adult examinees (age 18 to 85), inhabitants of the islands of Brac and Hvar and the Peljesac peninsula, Croatia. Interclass (for parent-offspring family pairs) and intraclass (for siblings) correlation coefficients have been calculated as well as heritability coefficient (h2) and coefficient quantifying effects of common sibling environment (c2) have been estimated. Heritability estimates (h2) for the medullary canal width dimensions (54%-71%) showed to be at least as high, and c2 (2%-14%) values showed to be at least as low as those obtained for bone length dimensions (h2 = 51%-65%; c2 = 5%-16%) suggesting a strong influence of genetic factors in medullary canal width formation. For both traits the highest heritability and the lowest environmental component is found for dimensions of 4th metacarpal bone, which could be explained by lower biomechanical pressures acting on that bone owing to it's anatomical position. Analysis of family resemblance for medullary canal width showed the tendency of female family pair (Mother-daughter) to be less correlated than other family pairs, which is especially pronounced in fourth metacarpals. We assume that lower correlation values of Mother-daughter pair can be the result of non-linearity of age dependent changes in medullary canal width dimensions associated with the osteoporotic process which is more active in females. Clearly lower heritability values obtained for total diaphysis width dimensions (25%-48%) and higher values obtained for c2 (14%-23%), in addition to findings of higher correlation values in same sex family pairs (Father-son, Mother-daughter) speaks in favor of substantial importance of common family environmental factors--particularly sexually specific physical activity--which through the short-term adaptation processes modify the total diaphysis width dimension phenotype.