From a Single Gene Defect Towards a Cross Species Neurocognitive Phenotype: The <em>EHMT1</em> Disruption Example (Kleefstra Syndrome)

Research Articles

Austin J Autism & Relat Disabil. 2015; 1(2): 1009.

From a Single Gene Defect Towards a Cross Species Neurocognitive Phenotype: The EHMT1 Disruption Example (Kleefstra Syndrome)

Karlijn Vermeulen1,2,3*, Wouter G. Staal1,3*, Joost G. Janzing², Jan K. Buitelaar1,3, Hans van Bokhoven3,4,5, Jos IM Egger6,7,8 and Tjitske Kleefstra3,4

¹Karakter Child and Adolescent Psychiatry University Centre, Netherlands

²Department of Psychiatry, Radboud University Medical Centre, Netherlands

³Department of Cognitive Neuroscience, Donders Institute for Brain, Cognition and Behavior, Radboud University Medical Centre, Netherlands

4Department of Human Genetics, Radboud University Medical Centre, Netherlands

5Centre for Molecular Life Sciences, Radboud University Nijmegen, Netherlands

6Centre for Cognition, Donders Institute for Brain, Cognition and Behavior, Radboud University Nijmegen, Netherlands

7Vincent van Gogh Centre of Excellence for Neuropsychiatry, Netherlands

8Behavioral Science Institute, Radboud University Nijmegen, Netherlands

*Both are equally contributing to this work

*Corresponding author: Tjitske Kleefstra, Department of Human Genetics, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, Netherlands

Received: March 07, 2015; Accepted: September 10, 2015; Published: September 25, 2015


Aim: Neuropsychiatric disorders comprise a clinically heterogeneous group of conditions that share underlying molecular and pathological mechanisms. Knowledge about how molecular pathways affect cognition and emotion is highly fragmentary. The Euchromatin Histon Methyl Transferase 1 (EHMT1) gene encodes a protein involved in chromatin modification and is presumed to have an important role in the etiology of cognitive and emotional dysfunctions. While animal studies with EHMT mutant species showed deviations in learning, attention and social cognition, systematic studies investigating behavioral characteristics in humans have been hardly conducted. Adult case studies showed behavioral disturbances with a sudden decline in functioning together with sleep problems. The focus of this report is to describe symptoms and developmental aspects in children with EHMT1 defects and compare these two previous studies in adults and animal models.

Methods: Four children with EHMT1 defects were investigated on adaptive functioning, psychiatric symptoms and temperament.

Results: All subjects have a severe developmental delay and meet the criteria for autism spectrum disorders, irrespective of severity of their intellectual disability. Three subjects have extreme sleep problems, while two subjects also have anxiety and mood disorders. Temperament is characterized by deficits in attentional focusing and inhibition.

Conclusion: These results show that EHMT1 defects severely affect cognitive processing, behavior and emotional functioning in children. This is in agreement with previous observations in animal studies and adult patients. The important role of EHMT1 in cognitive processing suggests that disruptions in a single gene can result in a broad spectrum of psychiatric pathology in human.

Keywords: Kleefstra syndrome; EHMT1 gen; Intellectual disability; Autism; Sleep; Behavior


Twin, adoption and molecular genetic studies have produced evidence that genetic factors are significant contributors to the etiology of several neuropsychiatric disorders and related traits. Although the genetic architecture of these disorders is complex, it has become evident that rare, moderate risk variants such as de novo Copy Number Variants (CNVs) are an important contributor to the disease risk [1-5]. Identification of harmful CNVs may be challenging, but even more difficult is defining how such genomic changes affect biological pathways and result in disease.

Known disruptions in a specific gene, well described in terms of biological functioning and associated phenotype will be of vital importance to understand the role of CNVs in neuropsychiatric disorders. Disruptions of EHMT1 are a clear example of a specific genetic abnormality that results in psychiatric symptoms. In a recent study using Next Generation Sequencing in humans with various cognitive dysfunctions, EHMT1 was identified as the only common mutated gene in an overlapping group of cognitive disorders: Intellectual Disability (ID), autism and schizophrenia [6]. The EHMT1 gene is located on 9q34 at the subtelomeric end. Either 9q34 micro deletions or intragenic EHMT1 mutations can similarly lead to impaired cognitive functioning [7]. The gene is expressed widely in neural tissue strongly suggesting that the EHMT1 gene plays an important role in neurodevelopment. The enzyme, for which it encodes, is capable to methylate lysine 9 of histone 3 (K9H3 methylase). Consequently, changes in chromatin modulation occur, thereby influencing epigenetic processes of gene regulation [8,9]

Importantly, the EHMT gene is studied cross species. Behavioral studies in Drosophila melanogaster and mice with EHMT defects have been performed [10,11] and show strong associations between EHMT defects and neurocognitive abnormalities. For example, in Drosophila, neurodevelopment and behavioral analyses identified EHMT as a regulator of larval loco motor behavior, non-associative learning, and courtship (complex) memory. Moreover, memory dysfunction was repaired by EHMT re-expression during adulthood, indicating that cognitive defects are reversible in EHMT Drosophila mutants [11]. Additionally, the study of heterozygous EHMT1 knockout mice demonstrated difficulties in the processing of novel stimuli, higher levels of anxiety and a deviation in social reaction to strangers [10].

In humans, mutations of EHMT1 result in a clinical syndrome, known as Kleefstra Syndrome (KS) or chromosome 9q sub telomere deletion syndrome [OMIM 610253]. Worldwide about 150 cases of this syndrome are reported so far [12-14]. The clinical picture of this syndrome is dominated by intellectual disability, hypotonia and characteristic facial dysmorphisms such as micro-/brachycephaly, mid-face hypoplasia, hypertelorism, synophrys with/without arched eyebrows, a short nose and tongue-protrusion. These can be accompanied by a variety of symptoms as congenital structural heart defects, uro-genital defects, epilepsy and severe behavioral disturbances.

Two recent reports pay attention to the behavioral characteristics in a few adults with the KS [15,16]. These patients showed clinical features like apathy and severe sleep problems and significant loss of functioning became apparent after adolescence with increasing symptoms over time. This “regressive” phenotype was suggested to be associated with the EHMT1 gene particularly since it was also observed in a patient with an intragenic EHMT1 mutation [16].

To date, no studies are reported that specifically and systematically investigate symptoms and behavioral characteristics of children with KS. Consequently, it is as yet unknown which symptoms do occur due to the EHMT1 mutation and to what degree.

Therefore, the present study focuses on mapping symptoms and developmental aspects in childhood and compares these to the results in animal studies and in adult patients, thereby connecting a single gene disruption with a biological pathway and with behavior. In addition, this cross species comparison may be of help in future studies that address development of therapeutic potentials of affected chromatin modification.

Materials and Methods


In this pilot study, four subjects with an EHMT1 defect participated: Three males etc., and one female. The participants were referred by the department of Human Genetics, Radboud University Medical Center Nijmegen, Netherlands. Informed consent was obtained from legal representatives (parents), because the subjects aren’t competent to sign for participation. However, if a subject indicated not wanting to participate or wanting to quit a task, then this was immediately followed by termination of the task or participation. The informed consent was signed by the parents on a consent form, which is included in the file of the participant. The regional medical ethics committee (Medical Ethics Committee of the Radboud University Medical Centre, Nijmegen, Netherlands) approved the consent procedure. Their ethics statement is positive about the investigation file.

Patient characteristics

Patient characteristics and developmental aspects are listed in table 1. Detailed descriptions of the subjects are added in the appendix. The medical and genetic characteristics of all cases have been published in short in previous clinical genetic studies; patient 1 was reported as patient 21 in [14] . Patient 2 and patient 3 were reported as patient 4 and patient 8 respectively in [7, 14], patient 4 was reported as patient 27 in [14]. Patient 1, 2 and 4 had an intragenic EHMT1 mutation; patient 3 had a 9q34.3 micro deletion encompassing entire EHMT1 and other genes (3.2 Mb).