The FMR1 gene has a pattern of DNA, called a CGG repeat.
The gene is located on every X chromosome; women have two X chromosomes (X,X) and men have one (X,Y).
Each person has a different number of CGG repeats at this site.
The FMR1 gene can undergo changes, when inherited, which can cause these Fragile X disorders.
The FMR1 gene usually has between 5 and 44 CGG repeats, with most people having 29 or 30.
Three different types of FMR1 expansions can occur:
- Full mutation
These expansions are defined by the number of CGG repeats.
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