An interstitial deletion of chromosome sub‐band Xp11.4, fusing USP9X to DDX3X (Supporting Information Figure 3A), was observed in 2/26 cases by SNP6.0 arrays and 7/24 cases by FISH, including one DS patient, giving an incidence of 19% (Supporting Information Figure 3B). Here, DDX3X is linked to Dravet syndrome.