Refining reproductive risk for FMR1 premutation carriers in the general obstetric population.

Female FMR1 premutation (FMR1 PM) carriers for fragile X syndrome (FXS) are at risk to have a child with FXS based on their CGG repeat size and AGG interruption number. Studies examining this risk in unselected populations of female PM carriers are lacking. This retrospective cohort study analyzed carrier status, CGG repeat length, AGG interruption result, and reproductive risk refinement in a population of female patients who underwent routine carrier screening for FXS. A total of 1536 PM carriers (0.43%) were identified, 95% of whom had between 55 and 90 CGG repeats. A number of 1334 carriers underwent AGG interruption testing. The majority had at least one AGG interruption and received a lower reproductive risk for FXS following AGG interruption testing (89% and 85%, respectively) as compared to their risk calculated based on CGG repeat size alone. The average change in risk across the population following AGG interruption testing was -3.4%, with a range from -50.8% to 48.9%. This article describes the range of CGG repeats and AGG interruptions in an unselected population of female PM carriers and suggests that most carriers would benefit from AGG interruption testing to refine their reproductive risk of having a child with FXS.