The exact number of people with a premutation is unknown. Research shows that about 1 in 151 females and 1 in 468 males may have an
FMR1 gene premutation, which puts them at risk for FXTAS.1 But not everyone with a premutation will show symptoms.
FXTAS is less common among women, and their symptoms are generally milder.2
In people with a premutation, 30% to 40% of men older than 503 and 8% of women older than age 50 will develop FXTAS.4
Seltzer, M. M., Baker, M. W., Hong, J., Maenner, M., Greenberg, J., & Mandel, D. (2012). Prevalence of CGG expansions of the FMR1 gene in a US population-based sample.
American Journal of Medical Genetics. Part B, Neuropsychiatric Genetics, 159B(5), 589–597.
National Fragile X Foundation (n.d.).
FXTAS vs FXS. Retrieved May 7, 2012,
Jaquemont, S., Hagerman, R. J., Leehey, M. A., Hall, D. A., Levine, R.A., Brunberg, J. A., et al. (2004) Penetrance of the fragile X associated tremor/ataxia syndrome in a premutation carrier population.
Journal of the American Medical Association, 291,460–469.
National Fragile X Foundation. (2011).
Prevalence of FXTAS. Retrieved May 7, 2012, from