However, they are unstableupon transmission to offspring and, when maternally transmitted, the premutation repeatmay eventually expand to (CGG)>200, thus characterizing the full mutationthat causes the Fragile X syndrome (FXS) as a result of FMRP deficiency.2 FXS is the most common cause ofinherited mental retardation.2,3 FXTAS is not the only conditionassociated with the premutation of the FMR1 gene. This evidence concerns the gene FMR1 and Intellectual disability.