In six families we identified five pathogenic mutations in three known XLID genes (SLC16A2, GRIA3 and DLG3) and one in the candidate XLID gene ZMYM3. In addition, two novel syndromes were identified, one with a novel missense mutation in a candidate XLID gene, ZMYM3[23] and the other with a previously reported benign variant in SYP in a large family (D175). The gene discussed is GRIA3; the disease is cask-related x-linked intellectual disability.