FMR1 and fragile X syndrome: Several case reports have also indicated that individuals mosaic for unmethylated PM and FM alleles express FMR1 mRNA from expanded PM and FM alleles, and have a fragile X-associated tremor/ataxia syndrome (FXTAS) phenotype, based on clinical assessments and MRI features [11–13]; though associations with other FXS characteristics have not been explored in large samples of FXS individuals.