It occurs in about 1 in 1500 males and 1 in 2500 females.
Early diagnosis allows genetic counseling, therapy and testing of at risk relatives.
The most common signs of Fra X are mental retardation, learning disabilities, and developmental delay. An individual with Fra X may be hyperactive, show signs of autism such as poor eye contact, have rapid repetitive speech , hand biting and flapping, hypersensitivity to light or sound, and difficulty in adapting to changes. Physical signs are most noticeable in adults and include enlarged testes after puberty, large head and hands, long narrow face with prominent chin and forehead and large flat ears. Children may have few identifiable physical characteristics. Females maybe less severely affected and the facial features are rarely seen.