<s>[INST] <<SYS>> This is a medical question of type : frequency <</SYS>> How many people are affected by fragile X-associated tremor/ataxia syndrome ? [/INST] Studies show that approximately 1 in 450 males has the genetic change that leads to FXTAS, although the condition occurs in only about 40 percent of them. It is estimated that 1 in 3,000 men over age 50 is affected. Similarly, 1 in 200 females has the genetic change, but only an estimated 16 percent of them develop signs and symptoms of FXTAS. </s>