How Does the FMR1 Gene Change From Stable to Premutation to Full Mutation?
A person who inherits fragile X syndrome does so as the result of a series of steps that occurred in their ancestors. The first step involves the shift from a stable version of the FMR1 (fragile X mental retardation) gene to an unstable version (premutation). This event is very rare. Once the first step has occurred, change is no longer rare. Instead it is common for someone with the premutation to pass on the full mutation to an offspring. We use the word “mutation” for an event and the result of that event. When part of the DNA is changed, that event is called a mutation. The variation that is a result of that event is also called a mutation. So we refer to a change in the number of repeats as a mutation event. We also say that someone who has more than 55 repeats has a mutation in their FMR1 gene. Stable to premutation Most people with the stable version (about 30 CGG repeats) pass on the stable version to their offspring. In other words, most people with the stable version pass on
