Kleefstra syndrome (KS) (OMIM#610253) is a rare genetic condition affecting at least 1 in 120,000 individuals who have a neurodevelopmental disorder and is caused by a mutation in euchromatin histone lysine methyltransferase 1 (EHMT1) gene or the deletion of a specific region of chromosome 9 that includes the EHMT1 gene (1–3). This evidence concerns the gene EHMT1 and Kleefstra syndrome.