| Mutation type | Number of CGG trinucleotide repeats | Methylation status of FMR1 | Clinical status | |
| Male | Female | |||
| Premutation | Approximately 55 to 200 | Unmethylated | At risk for FXTAS* | At risk for POI and FXTAS |
| Methylated full mutation | >200 | Completely methylated | 100% with intellectual disability | Approximately 50% with intellectual disability, approximately 50% normal intellect |
| Repeat size mosaicism | Varies between premutation and full mutation in different cell lines | Partial: Unmethylated in the premutation cell line; methylated in the full mutation cell line | Nearly 100% affected with ID; may be higher functioning¶ than males with full mutation | Highly variable: Ranges from normal intellect to affected |
| Methylation mosaicism | >200 | Partial: Mixture of methylated and unmethylated cell lines | Nearly 100% affected with ID; may be higher functioning¶ than males with full mutation | Highly variable: Ranges from normal intellect to affected |
| Unmethylated full mutation | >200 | Unmethylated | Nearly all have ID but often have high functioning ID to low-normal intellect | Highly variable: Ranges from normal intellect to affected |
CGG: cytosine-guanine-guanine; FMR1: fragile X mental ribonucleoprotein 1; FXTAS: fragile X-associated tremor/ataxia syndrome; POI: premature ovarian insufficiency; ID: intellectual disability; IQ: intelligence quotient.
* Both males and females with premutations and manifestations of some symptoms of fragile X syndrome have been reported[1].
¶ FMR1 mutations are complex alterations involving nonclassic gene-disrupting alterations (trinucleotide repeat expansion) and abnormal gene methylation. This complexity at the gene level affects production of the FMR1 protein and may result in an atypical presentation in which affected individuals occasionally have an IQ above 70, the traditional demarcation denoting mental retardation.Reproduced with permission from: Saul RA, Tarleton JC. FMR1-Related Disorders (August 2008). In: GeneReviews at GeneTests: Medical Genetics Information Resource (database online). Copyright © University of Washington, Seattle. 1997-2010. Available at: http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene∂=fragilex (Accessed on December 22, 2009).
