Neuroanatomy of fragile X syndrome: the temporal lobe

Fragile X syndrome, an X-linked genetic disorder caused by a mutation in the FMR-1 gene, is associated with a particular profile of abnormalities of behavior, learning, language, and memory, suggesting temporal lobe dysfunction. We undertook a quantitative neuroimaging study investigating the neuroanatomy of the temporal lobe in individuals with the fragile X mutation. The temporal lobe neuroanatomy of 15 young fragile X subjects was quantified and compared with that of 26 age- and IQ-matched control subjects. Analyses showed the right and left hippocampal volumes to be significantly larger in the fragile X group compared with the control group. Subjects with the fragile X mutation showed an age-related increase in volume of the hippocampus an age-related decrease in volume of the superior temporal gyrus. Along with the findings of previous imaging studies of fragile X subjects, the results of the present investigation are consistent with studies showing a nonrandom distribution of expression of the FMR-1 gene in the developing brain, with increased expression in the cerebellum, hippocampus, and specific cortical regions. The results also suggest involvement of temporal lobe regions in the behavioral and cognitive abnormalities associated with fragile X syndrome.