Fragile X syndrome (FXS) is a genetic disorder. Symptoms often include mild to moderate intellectual disability. The average IQ in males is under 55. Physical features may include a long and narrow face, large ears, flexible fingers, and large testicles. About a third of those affected have features of autism such as problems with social interactions and delayed speech. Hyperactivity is common and seizures occur in about 10%. Males are usually more affected than females.Fragile X syndrome is inherited in an X-linked dominant pattern. Women with a premutation have an increased risk of having an affected child. It is typically due to an expansion of the CGG triplet repeat within the Fragile X mental retardation 1 (FMR1) gene on the X chromosome. This results in not enough fragile X mental retardation protein (FMRP), which is required for the normal development of connections between neurons. Diagnosis is by genetic testing to determine the number of CGG repeats in the FMR1 gene. Normal is between 5 and 40 repeats, fragile X syndrome occurs with more than 200, and a premutation is said to be present when a middle number of repeats occurs. Testing for premutation carriers may allow for genetic counseling.There is no cure. Early intervention is recommended as it provides the most opportunity for developing a full range of skills. These interventions may include special education, speech therapy, physical therapy, or behavioral therapy. Medications may be used to treat associated seizures, mood problems, aggressive behavior, or ADHD. Fragile X syndrome is estimated to occur in 1.4 in 10,000 males and 0.9 in 10,000 females.