Abstract
A decline in IQ through childhood has been reported by several centers in boys with fragile X syndrome. Fisch et al. have recently reported that girls with fragile X syndrome have a similar decline in IQ through childhood. This study is a longitudinal follow-up of cognitive testing in 21 girls who are cytogenetically positive and have fragile X syndrome. Fourteen had DNA testing and all demonstrated the full mutation except one who had a high end premutation and 10% cytogenetic expression. The control population consisted of 18 females who were fragile X negative with a variety of developmental problems and IQs and ages comparable to the fragile X patients. Cognitive testing utilized the Stanford Binet, the Wechsler Scales and the Kaufman Assessment Battery for Children. The IQ scores were transformed to z scores for comparisons. The mean age for the first IQ test was 11, and the mean age for the final test was 16 years in the patients with the fragile X syndrome. A significant IQ decline was seen in 29% of the fragile X patients and 22% of the controls (p = 0.69). The girls with the highest initial IQ were at greatest risk for a significant decline (p < 0.001). Overall 24% of the girls with fragile X syndrome were mentally retarded (IQ < 70). Although a limited group of girls with fragile X syndrome experience a significant IQ decline, this is a less severe problem than what has been reported in boys with fragile X syndrome. The decline in IQ in girls with fragile X syndrome is comparable to controls, but further studies are necessary to assess possible predictive factors in molecular or FMRP studies so that the subgroup at high risk for IQ decline can be identified early and receive optimal intervention.