FMR1 and fragile X syndrome: In this trial, ZYN002 was well tolerated in patients with FXS and demonstrated evidence of efficacy with a favorable benefit risk relationship in patients with ≥ 90% methylation of the promoter region of the FMR1 gene, in whom gene silencing is most likely, with little or no FMRP production, and the impact of FXS is typically most severe.