INSULIN-LIKE GROWTH FACTOR-I COMPARISONS IN HEALTHY TWIN CHILDREN

Insulin-like growth factor-I (IGF-I) levels in plasma were measured in healthy twin children. The within-pair correlation for 43 monozygotic pairs was r = 0.91 (P less than or equal to 0.0001), an association s ignificantly higher than that for same sex dizygotic pairs (r = 0.40; P less than or equal to 0.06). The high correlation for monozygotic tw ins indicated a marked genetic influence on IGF-I levels. After correc tion for age and sex, the correlation between IGF-I level and height w as r = 0.38 (P less than or equal to 0.0001). These findings provide c lear evidence that IGF-I levels correlate with height, a growth charac teristic known to be genetically controlled.