Intra-pair similarity in physical growth of monozygotic and of dizygotic twins during puberty.

The growth of 323 pairs of twins (94 MZ pairs, 133 DZ like-sexed pairs and 97 DZ unlike-sexed pairs) born in 1954/55 was studied longitudinally from 10 to 18 years for boys and 10 to 16 years for girls. Within-pair comparisons for height and weight have been made for MZ twins and DZ like-sexed twins. A significantly higher concordance in height was found for MZ pairs than for DZ pairs during puberty, for both boys and girls. Yearly height increments were also more similar for the MZ pairs, showing that the height spurt occurs more simultaneously for MZ twins in comparison to DZ twins. Height seems to be a strongly genetically regulated variable. The MZ twins also show a high concordance in weight during the whole investigation period. The DZ pairs, however, became progressively less similar in weight. This is most pronounced for the DZ girls, the intra-class correlation for weight decreasing from 0.66 at 10 years to 0.23 at 16 years. This could imply stronger interactional effects for girls than for boys with regard to weight during puberty.