Fragile X mental retardation is a prominent genetic disorder caused by the lack of the FMR1 gene product a known RNA binding protein. Specific physiologic pathways regulated by FMR1 function have yet to be identified. Adult dfmr1 (also called dfxr) mutant flies display arrhythmic circadian activity and have erratic patterns of locomotor activity whereas overexpression of dFMR1 leads to a lengthened period. dfmr1 mutant males also display reduced courtship activity which appears to result from their inability to maintain courtship interest. Molecular analysis fails to reveal any defects in the expression of clock components; however the CREB output is affected. Morphological analysis of neurons required for normal circadian behavior reveals subtle abnormalities suggesting that defects in axonal pathfinding or synapse formation may cause the observed behavioral defects.
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