The epidemiology of FXTAS

Abstract

The prevalence of the FMR1 premutation ranges from 1/116 to 1/259 in women and from 1/251 to 1/1,250 in men. Population studies investigating the prevalence of FXTAS in the general population have not been conducted due to the rarity of the disorder. The prevalence of FXTAS is estimated to be 1/4,000 in men over the age of 55, due to age-dependent penetrance. The prevalence in women is thought to be much lower, at approximately 1/7,800, because of the protection of the second X chromosome. Many screening studies have been conducted in movement disorder populations, attempting to ascertain undiagnosed FXTAS cases and premutation expansions. These studies have yielded low rates, with a rate of 1.3% in cerebellar ataxia patients, <1% in parkinsonian disorders, such as Parkinson disease and multiple system atrophy, and 0% in essential tremor. Screening studies vary widely in the type of patients included, both in ethnicity and in gender. Wider inclusion criteria for screening should increase the rates of ascertainment of both FXTAS and premutation expansions in future studies.