Fragile x premutation is a genetic condition defined by an intermediate expansion of the CGG trinucleotide repeat (typically 55-200 repeats) in the 5' untranslated region of the *FMR1* gene, serving as a key research area investigating its molecular mechanisms, associated clinical phenotypes (such as Fragile X-associated Tremor/Ataxia Syndrome and Fragile X-associated Primary Ovarian Insufficiency), and implications for carrier health and risk of having children with Fragile X Syndrome.