FMR1 and fragile X syndrome: To test our hypothesis that folate deficiency could affect the stability of regions containing large number of repeats, we started our analysis with a FXS mutant cell line GM09237, which is known to contain more than 900 CGG repeats at the FRAXA locus (Vincent et al., 1991; Seneca et al., 2012) and display missegregation in mitosis when it is cultured under folate stress conditions (Bjerregaard et al., 2018).