Variability in FMRP and early development in males with fragile X syndrome

To test the hypothesis that variability in development in fragile X syndrom e is related to FMRP (the protein deficient in this syndrome expression), w e studied 53 males between 23 and 98 months of age. For the entire group, w hich included males with either mosaism, partially methylated full mutation , and fully methylated full mutation, FMRP expression ranged from 1% to 40% and accounted for a small but significant amount of variance in level, but not rate, of total development as well as motor, social, adaptive, cogniti ve, and language development. For males with a fully methylated full mutati on, the association was in the hypothesized direction, but not statisticall y significant. Findings support the hypothesized relationship between FMRP and individual capabilities but suggest that other factors also play a majo r role.