Kleefstra Syndrome

is a rare genetic condition.

is caused by the loss of function in the EHMT1 gene (chromosome 9).

affects development and involves many body systems.

What are the symptoms and causes?

People with Kleefstra Syndrome (KS) usually have distinct facial features, developmental delay, intellectual disability, low muscle tone (hypotonia) and communication difficulties. Kleefstra syndrome causes a range of symptoms that can differ from person to person.

Kleefstra syndrome is caused by a mutation in a gene called EHMT1 or the deletion of a specific region of chromosome 9 that includes EHMT1. Other names for Kleefstra syndrome include 9q-syndrome, 9q34.3 deletion syndrome, and chromosome 9q deletion syndrome.

Kleefstra syndrome is caused by the loss of function of one copy of the EHMT1 gene. In about 50 percent of cases, a variation or “mutation” in one copy of the EHMT1 causes the loss of function. The remaining cases are caused by the deletion of one copy of a segment of chromosome 9, which includes the gene EHMT1.

The role of EHMT1 is to produce an enzyme, histone methyltransferase 1, that controls the activity of other genes in the body. When one copy of EHMT1 loses its function, it affects a large number of other genes involved in development and functioning of organs and tissues throughout the body.

Individuals with Kleefstra syndrome have one standard copy of EHMT1 and one that does not work or is deleted. This means they have a 50 percent chance of passing the condition on with each pregnancy. Almost all cases reported have been de novo (not inherited).



We lead the Kleefstra Syndrome Europe Alliance.

The Kleefstra Syndrome Europe Alliance is a central coordination hub for Kleefstra syndrome (type 1) in Europe. The hub brings together national Kleefstra patient organisations and groups from Europe. We work together to improve the lives of our children with Kleefstra syndrome (type 1, gene EHMT1) by providing contacts and information to national and regional contact points for families affected by Kleefstra syndrome.

National Kleefstra patient organizations in Europe (click on the map)

Outside Europe

Kleefstra sydrome USA (IDefine)
Kleefstra syndrome Japan
Kleefstra syndrome community in South America
Kleefstra syndrome community in Canada
Kleefstra syndrome community in Australia

For more information you may contact IDefine Europe for Europe related inquiries at info@idefine-europe.org and IDefine for America/Canada/Australia related questions.

We are part of the international Kleefstra syndrome movement.

The international Kleefstra syndrome movement advocates for Kleefstra syndrome to be recognised as a rare disease and to be researched as much as possible. We strive to include all Kleefstra syndrome cases worldwide. That is the mission of the Kleefstra Syndrome worldwide map. It displays the locations of KS individuals around the globe.

By adding your child or relative with Kleefstra syndrome to the map, you will help determine the prevalence of Kleefstra syndrome. To do so go to https://www.kleefstraworldmap.org/.

Active data collection projects/surveys for Kleefstra syndrome:

Share valuable information about your child to support the collection of patient data and help accelerate progress. Click on the provided logos below and you will be diverted to the survey site/data collection platform for Kleefstra syndrome. 

RARE-X is a collaborative platform for global data sharing and analysis to accelerate treatments for rare disease.

By joining AllStripes, you can contribute your de-identified medical records to multiple research efforts.

Accelerate knowledge about genetic forms of intellectual disability, autism and epilepsy by sharing caregiver-reported data.

Research into speech and language skills in individuals with Kleefstra syndrome.