This disorder and finding of Fragile X syndrome has an X-linked dominant inheritance. It is typically caused by an expansion of the CGG triplet repeat within the "FMR1" (fragile X mental retardation 1) gene on the X chromosome. This results in silencing (methylation) of this part of the gene and a deficiency of the resultant protein (FMRP), which is required for the normal development of connections between neurons. Diagnosis requires genetic testing to determine the number of CGG repeats in the "FMR1" gene. Normally, there are between 5 and 40 repeats; fragile X syndrome occurs with more than 200. A premutation is said to be present when the gene has between 40 and 200 repeats; women with a premutation have an increased risk of having an affected child. Testing for premutation carriers may allow for genetic counseling.