FMR1 and fragile X syndrome: Whereas full mutation CGG-repeat expansions (>200 repeats) of the fragile X gene (FMR1) give rise to the neurodevelopmental disorder, fragile X syndrome (FXS); smaller, ‘premutation’ expansions (55 to 200 repeats) are now gaining increasing recognition as the basis for a spectrum of clinical involvement, from neurodevelopmental problems, to mid-adult disorders, such as the fragile X-associated primary ovarian insufficiency (FXPOI) and mood and psychiatric disorders, to the late-adult-onset neurodegenerative disorder, fragile X-associated tremor/ataxia syndrome (FXTAS).