- Fragile X
- Treatment & Intervention
- Support the NFXF
There have been a number of studies aimed at determining 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 3,600 to 4,000 and in females is approximately 1 in 4,000 to 6,000.
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.
These statistics are important because both men and women are at risk for having symptoms linked to Fragile X-associated Disorders.
This study of 6,747 older adults in Wisconsin found 30 people with a change in the FMR1 gene. Based on this relatively small number of people, the results should be interpreted with caution. These findings may not reflect all people in the United States with an FMR1 premutation For example a large Israeli study found approximately 1/130 women were FMR1 carriers.
Current estimates suggest that about 30-40% of male FMR1 premutation carriers over 50 years of age, within families already known to have someone with Fragile X, will ultimately exhibit some features of FXTAS.
This figure may be as low as 10-20% in the general population, since the majority of carriers have a premutation in the lower range of CGG repeats, where the occurrence of FXTAS appears to be reduced.
Though there are specific diagnostic criteria for FXTAS, some men may only exhibit some of the symptoms, and may not develop all of the cardinal features of the condition.
For men who are premutation carriers, the chance of developing core symptoms of FXTAS (tremor, problems with walking/balance) increases with age.
Studies of females have found that about 8-16% of premutation carriers, within families already known to have someone with a Fragile X condition, develop some FXTAS symptoms. The symptoms in females tend to be milder.
FXTAS may be one of the most common adult onset, single-gene neurological diseases; similar in prevalence to other neurodegenerative diseases such as ALS (Lou Gehrig’s disease); however more studies within the general population will be necessary before the true incidence is known.
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 FXDs or to have children with Fragile X syndrome.
Based on the best available evidence: