NORMAL VARIATION IN SIZE OF THE FMR1 GENE IS NOT ASSOCIATED WITH VARIATION IN INTELLECTUAL-PERFORMANCE

The fragile X mental retardation (FMR1) gene was examined as a potenti al single-gene candidate for variation in intelligence score, on the b asis of its well established relation with mental retardation. The siz e of the normal FMR1 gene varies across individuals, and is measured b y the number of cytosine-guanine-guanine (CGG) repeats of which it is comprised. In this study, the association between IQ score and the num ber of CGG repeats was examined among 917 school age children, includi ng 455 Caucasian children and 462 African American children. Separate analyses were conducted with the entire sample, with girls and boys ex amined separately, and with Caucasian and African American subgroups. None of the models revealed a statistically significant association be tween IQ and number of CGG repeats. The results from this study provid e strong evidence that variation in CGG size, among normal size FMR1 a lleles, does not account for variation in intelligence.