Prevalence of FXTAS
Current estimates suggest that about 30-40 percent of male FMR1 premutation carriers over 50 years of age, within families already known to have someone with a Fragile X-associated disorder, 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 (see Testing and Diagnosis), some men may only exhibit some of the symptoms, and may not develop all of the cardinal features of the condition. (See Symptoms in Males) The chance of developing core symptoms of FXTAS (tremor, problems with walking/balance) increases with age. From age 50-59 the chance is about 17 percent, from age 60-69 about 38 percent, from age 70-79 about 47 percent, and in males over 80 years old, about 75 percent will develop symptoms of FXTAS.
Studies of females have found that about 8-16 percent of premutation carriers, within families already known to have someone with a Fragile X-associated disorder, develop some FXTAS symptoms. The symptoms in females tend to be milder. (see Symptoms in Females)
Research to date indicates that approximately 1 in 100 to 260 females and 1 in 260 to 813 males in the general population are carriers of an FMR1 premutation. This would indicate that about 1 in 3000 men and about 1 in 5200 women in the general population will develop symptoms of FXTAS. 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.