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The aim of the present study was to examine the heritability of 11 traits in a mixed-longitudinal sample of Indian siblings, and to determine whether heritability estimates vary during the growth period and whether they are influenced by sex. The sample consisted of 245 brothers and 213 sisters from 138 nuclear families living in a semi-urban area in Kolkata, India. The age ranged between 5 and 19 years. The traits were standardised for age and sex using standard deviation scores (SDS) produced by the LMS method (Cole, T.J., 1988. Fitting smoothed centile curves to reference data. J. R. Stat. Soc. A 151, 385-418). The standard deviation scores were analysed by PCA. The two factors with eigenvalues above 1 explained 77.3% of the variance; they showed a high level of pleiotropism present among the studied traits and represented body lengths (PC1) and body weight and breadths (PC2). The heritability between all types of siblings (irrespective of sex) for the PC1 and PC2 was estimated. The heritability between various pairs of siblings showed variations along the whole ontogenetic period studied. During the childhood and pre-pubertal period, heritability between brothers, brother-sister pairs and any sibling pairs was mostly constant, with small and non-significant variations. All the pairs showed the lowest degree of heritability during puberty for PC1 but not for PC2, with significant changes of heritability estimates between adolescence and adulthood, in most of the analysed sibling pairs and in both PC factors. The highest heritability was generally observed at the end of the examined growth period in all pairs. A significant effect of sex on heritability was only detected for PC2 at 11 years of age.

Background: Even though some studies have considered that sibling resemblance remains constant throughout the life cycle, several investigations emphasize the importance of age and its interactions with genetic and environmental factors in determining sibling similarity in several bodily traits. In fact, the study of age changes in familial resemblance is of great importance for the analysis of certain sources of variation observed in growth processes., Aim: The study examined sibling resemblance for height, weight and body mass index (BMI) in a mixed longitudinal sample from West Bengal, ages 2-19 years, in order to analyse the variations with age of the sibling resemblance for these phenotypes during growth., Sample and Methods: Two hundred and forty-five brothers and 213 sisters from 138 middle-class nuclear families living in a semi-urban area of South Kolkata, India were analysed. The analysis of sibling resemblance was performed through correlations estimated by the maximum-likelihood method. The patterns of different trends of sibling resemblance with age were examined by fitting a cubic non-linear regression to the observed correlations., Results: The results show clear variations with age in the sibling resemblance for the traits height and weight, though to a lesser extent for BMI. In general, we found the highest correlation values during the period of infancy, a remarkable decrease during puberty, and a trend of increase towards the end of the growth cycle., Conclusion: The study confirms the effect of age on the degree of similarity among siblings for height, weight and BMI in the sample. The sharp decline of correlation at adolescence can be interpreted in terms of the individual variation in age of reaching the adolescent growth spurt.

Background: Longitudinal and semi-longitudinal growth studies on siblings reflecting heritability changes during growth are very scarce. Moreover, studies of variables other than height, weight and BMI are virtually non-existent. Aim: The study compared changes in the heritability of six body lengths, four body breadths, and three indices between ages 4 and 19 years on the basis of a mixed-longitudinal sample of siblings, and examined whether heritability estimates change during the growth period. The data consisted of 238 brothers and 214 sisters from 134 middle-class nuclear families living in Kolkata (India). The analysis of sibling correlation was performed by maximum likelihood. The age-related patterns of heritabilities of the various traits were described by a cubic spline. Results: The heritability was very high and significant in most traits, and at all considered ages. Mean heritability in the 10 morphometric traits was 69.3%, which was higher than the heritability values for the three indices. Conclusions: These results confirmed the existence of age-related trends in heritability of the considered morphometric traits. The sharp decline of the heritabilities at adolescence in most of the morphometric traits, and the acromio-iliac index in particular, may be due to the large inter-individual variation in the age at which the adolescent growth spurt is reached in both sexes. [ABSTRACT FROM AUTHOR]

We analysed the Heath-Carter somatotype familial resemblance degree in a sample of 1350 siblings (685 males and 665 females) from 634 nuclear families in the province of Biscay (Basque Country, Spain). Sibling correlations were estimated according to maximum likelihood procedures for endomorphy, mesomorphy, ectomorphy and somatotypical attitudinal distance (SADi), after having adjusted for age, sex and the two other components (Model I), and after taking into account several environmental variables shared by all members of each sibship (Model II). All sibling correlations of the somatotype components were significant, tending to be higher in the case of mesomorphy than in the case of endomorphy. Same-sex siblings (BB and SS) displayed significant mesomorphic and ectomorphic resemblances, but in the case of endomorphy, sisters (SS) revealed relatively low correlation compared with brothers (BB). The sex of sibs had a significant influence on correlations of mesomorphy, but not on the other two components. Further control of socio-familial variables such as the father's occupation and education, and the sibship size, resulted in lower mesomorphy correlation coefficients, but had no effect whatsoever on the other two components. SADi correlations were very low and not significant, indicating high degrees of dispersion in the individual somatotypes of the sample. [ABSTRACT FROM AUTHOR]