When does a fragile X premutation become full mutation?

Fragile X syndrome (FXS) is caused by a mutation in the FMR1 gene. Premutation is an intermediate allelic state between a normal allele and a full mutation. Premutation carriers have an increased risk of developing various health conditions, including fragile X-associated tremor/ataxia syndrome (FXTAS) and fragile X primary ovarian insufficiency (FXPOI). A fragile X premutation becomes a full mutation when the number of CGG repeats in the FMR1 gene increases from the premutation range (55–200 repeats) to the full mutation range (>200 repeats). This expansion can occur over several generations or can happen spontaneously in an affected individual.