The first X-exome sequencing study of Finnish families with intellectual disability revealed the first two Finnish families with Allan-Herndon-Dudley syndrome, one family with a novel mutation in GRIA3, and two families with novel mutations in DLG3. In addition, a novel missense mutation in the candidate XLID gene ZMYM3 cosegregated with a novel syndrome. The gene discussed is ZMYM3; the disease is Allan-Herndon-Dudley syndrome.