Genetic analysis of growth curve parameters of body weight, height and head circumference

A sample of 681 Israeli boys and girls, including 355 regular siblings (SB) , 112 pairs of dizygotic (DZ) and 51 pairs of monozygotic (MZ) twins, was m easured for body weight (WT), length (HT) and head circumference (HC) at bi rth and during the first year of life. The Count model with three parameter s was chosen as the best fitting and most parsimonious function to approxim ate growth of the studied traits. The curves' fitting parameters were estim ated for WT, HT and HC for each individual. To test the assumption that the re is a genetic source influencing the pattern of growth for each trait, fa milial correlations between parameter estimates were computed for MZ, DZ tw ins and SE. In all instances MZ twins showed the highest within-pair correl ation in parameters of growth (from 0.58 to 0.86), while SE showed the lowe st ones (from 0.10 to 0.70). Variance decomposition analysis was used to si multaneously assess the contribution of gender, gestational age, additive g enetic factor, common sibs and common intrauterine environmental effects on total variance of each studied trait separately. All these sources of vari ation were statistically significant, though the effect of intrauterine env ironment played a substantial role in early stages of child physical develo pment, explaining from 18.1% to 70.6% of the total variance of the growth c urve parameters. Further analyses are needed to clarify holy this environme nt affects child growth and for how long.