- Fragile X-associated Disorders
- Treatment & Intervention
- Support the NFXF
There have been a number of studies aimed to determine the prevalence of FXS in males and females. Studies have been undertaken both in the “special needs” population and the general population. The agreed upon prevalence of FXS in males is approximately 1 in 3600 to 4000 and in females is approximately 1 in 4000 to 6000. The reason it is lower in females is that, while all males with an FMR1 full mutation will have fragile X syndrome, some females with an FMR1 full mutation will not have behavioral, cognitive or physical features of FXS.
General population studies in both the newborn and adult populations have found that approximately 1/260 females and 1/800 males are carriers of the FMR1 premutation worldwide. There may be some variation in some populations. For example a large Israeli study found approximately 1/130 women were FMR1 carriers. However, at this time, the accepted carrier rates internationally stand at approximately 1/260 females and 1/800 males
Approximately 1 in 50 (2%) of individuals have an intermediate allele. There appear to be no clinical associations with intermediate alleles. Most intermediate alleles are stable and do not change over generations. In a small number of families intermediate alleles show some slight instability and can lead to a premutation in future generations. Individuals with an intermediate allele are not at risk for any for the FXD’s or to have children with fragile X syndrome.
Based on the best available evidence: