Kleefstra syndrome (Ks) is a rare genetic disorder characterised by intellectual disability, often accompanied by a spectrum of complex physical and clinical features. The predominant cause of Ks is a tiny piece missing (known as a deletion) from near the end of chromosome 9. However individuals with a mutation, or intragenic duplication also carry a Ks diagnosis. The deletion or mutation affects a gene called EHMT1 (Euchromatic Histone Methyltransferase 1) and it's absence or disturbance is believed to cause the major symptoms of the syndrome. The syndrome was officially recognised as Kleefstra syndrome in April 2010. Ks has previously been known as 9q34.3 deletion syndrome, 9qSTDS (short for 9q subtelomeric deletion syndrome), 9q-Syndrome, 9q34.3 microdeletion syndrome.