Of the 13 patients with XLID, 7 (53.8%) patients (2 males, 5 female) had de novo variants, 5 male patients harbored hemizygous variants inherited from their asymptomatic heterozygous mother, and 1 female (patient 70) inherited the heterozygous variant c.445C > T in PCDH19 from her non-symptomatic father. Here, PCDH19 is linked to cask-related x-linked intellectual disability.