FMR1 and fragile X syndrome: Whereas FXS has a prevalence of around 1 in 4,000 males and 1 in 7,000–10,000 females, the FMR1 premutation (PM; FMR1 expansion between 55 and 200 CGG repeats) is more prevalent and occurs in approximately 1 in 468 males and 1 in 151 females in the United States (Seltzer et al., 2012).