In our previous RCT study conducted between 2016 and 2019, boys with FXS were included if they had a confirmed genetic diagnosis of FXS (> 200 CGG repeats on the FMR1 gene with evidence of aberrant methylation), were aged between 3 and 10 years inclusive, and exhibited at least one form of challenging behavior daily on the Behavior Problems Inventory–Short Form (BPI-S) [21]. The gene discussed is FMR1; the disease is fragile X syndrome.