What are CGG repeats
Fragile X is caused by a lengthening in the FMR-1 gene on the X chromosome. The change is an increase in the size of a small section of the FMR-1 gene. This gene is responsible for producing a protein called the FMR-1 protein which is necessary for normal brain function.
Part of the FMR-1 gene is made up of the chemical bases, CGG, repeated a number of times. The number of CGG repeats varies from one person to another and can be classified as being in the normal range if these repeats are between 1-50, the intermediate range of 50-58 repeats, the premutation range of 59-200 repeats and the full mutation range of over 200 repeats.
An intermediate or premutation range does not stop the gene from functioning and producing the FMR-1 protein.