Fragile X syndrome 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 normal development of the connection between neurons. Diagnosis is by genetic testing to determine the number of CGG repeats in the FMRI 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 occur. Testing for premutation carriers may allow for genetic counseling.
how did fragile x syndrome get its name
expansion of the CGG triplet repeat within the Fragile X mental retardation 1 (FMR1) gene on the X chromosome