FMR1 and fragile X syndrome: In addition, FMR1 levels are elevated in most tissues in FXTAS patients and CGG repeat expressing mice, despite probable compensatory mechanisms related to FXR1 and FXR2 functions in these tissues and the lack of a significant tissue phenotype in FXS patients [3], [10], [11], [57]; it is unclear why there would be a strong feedback trigger for transcription of FMR1 in tissues where its function is not clearly essential.