Influence of the fragile X mental retardation (FMR1) gene on the brain and working memory in men with normal FMR1 alleles.

The fragile X mental retardation 1 (FMR1) gene plays an important role in the development and maintenance of neuronal circuits that are essential for cognitive functioning. We explored the functional linkage(s) among lymphocytic FMR1 gene expression, brain structure, and working memory in healthy adult males. We acquired T1-weighted and diffusion tensor imaging from 37 males (18-80 years, mean ± SD= 40.7 ± 17.3 years) with normal FMR1 alleles and performed genetic and working memory assessments. Brain measurements were obtained from fiber tracts important for working memory (i.e. the arcuate fasciculus, anterior cingulum bundle, inferior longitudinal fasciculus, and the genu and anterior body of the corpus callosum), individual voxels, and whole brain. Both FMR1 mRNA and protein (FMRP) levels exhibited significant associations with brain measurements, with FMRP correlating positively with gray matter volume and white matter structural organization, and FMR1 mRNA negatively with white matter structural organization. The correlation was widespread, impacting rostral white matter and 2 working-memory fiber tracts for FMRP, and all cerebral white matter areas except the fornix and cerebellar peduncles and all 4 fiber tracts for FMR1 mRNA. In addition, the levels of FMR1 mRNA as well as the fiber tracts demonstrated a significant correlation with working memory performance. While FMR1 mRNA exhibited a negative correlation with working memory, fiber tract structural organization showed a positive correlation. These findings suggest that the FMR1 gene is a genetic factor common for both working memory and brain structure, and has implications for our understanding of the transmission of intelligence and brain structure.