Abnormal repeats in FMR1 in the so-called premutation range of 55–200 repeats express as FXTAS whereas more than 200 repeats manifests as FXS (4), markedly reducing the expression of FMR1. Despite the shared genetic background, these two conditions have discrepant phenotypes. This evidence concerns the gene FMR1 and fragile X-associated tremor/ataxia syndrome.