FMR1 and fragile X syndrome: Aside from tandem repeat polymorphism, mutations in the coding region of FMR1 have also been associated with the occurrence of FXS in patients (Quartier et al., 2017): a deletion of the last exon, which is giving rise to a truncated FMRP isoform, was recently identified in three brothers meeting FXS criteria (Hagerman’s scores = 15).