Age variations in sibling correlations for height, sitting height and weight

Familial correlations for height, sitting height and weight have been studied in a sample of 1278 siblings for the Biscay province (Basque Country), aged 4+ to 24+ years. The data have been internally standardized according to sex and age of individuals. The degree of resemblance among sibling has been expressed by intraclass correlation coefficients. The total sample has been divided into three age categories: < 12 years, 12-15 years, and > or = 15 years, in order to examine the effect of age on sibling correlations. In general, changes with age have been observed: sibling correlations for height show a clear upward trend through the considered growth period, reaching a value of 0.48 from 15 years of age. Intra-correlations for weight show a slight downward trend with age. Sitting height shows a rather low correlation before 12 years of age, but equally high values in the other two ranges of age (0.48 and 0.47, respectively). This study confirms that the sibling resemblance for the analysed trait fluctuated through the growth period--height and sitting height showing similar patterns of variation with age--and that, after puberty, the degree of genetic determination is higher for bone measurements than for weight.