The FMR1 gene can undergo changes that cause these Fragile X-associated disorders.
These changes affect a pattern of DNA called CGG repeats.
Typically, the FMR1 gene has up to 54 CGG repeats.
A premutation in the FMR1 gene results in 55–200 CGG repeats, and a full mutation in more than 200 CGG repeats.
The range of 45-54 is called the “gray zone.”