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Disease Profile


Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.


US Estimated

Europe Estimated

Age of onset





Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable


Other names (AKA)

IQSEC2-related intellectual disability; IQSEC2-related epilepsy; X-linked intellectual disability 1/78;


IQSEC2 is a genetic condition that causes intellectual disability and sometimes other physical, neurological, or psychiatric symptoms.[1] People with this condition can have seizures that are often difficult to control with medications. Other symptoms may include motor and language development delay, regression of learning abilities, autistic-like behavior, characteristic hand movements, and behavioral problems. Physical features may include abnormal head shape (plagiocephaly), very small head (microcephaly), reduced muscle tone (hypotonia), and crossed eyes (strabismus). This condition is caused by mutations in the IQSEC2 gene, which is located on chromosome X.[1][2][3] Depending on the severity of the gene mutation, the features can range from only intellectual disability to a syndrome that includes the other symptoms. In general, males are more affected than females.[1] Most cases are not inherited from a parent but are caused by a new (de novo) mutation. When the condition is inherited, the pattern is called X-linked recessive. There is no specific treatment, but early intervention and other services can support development. Seizure medications such as lamotrigine and rufinamide have been reported to control seizures in some people.[4]


This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

Medical Terms Other Names
Learn More:
5%-29% of people have these symptoms
Postnatal microcephaly
Percent of people who have these symptoms is not available through HPO
Short and broad skull
Generalized hypotonia
Decreased muscle tone
Low muscle tone

[ more ]


[ more ]

Intellectual disability
Mental deficiency
Mental retardation
Mental retardation, nonspecific

[ more ]

Poor speech
Squint eyes

[ more ]

X-linked dominant inheritance
X-linked recessive inheritance


Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

Social Networking Websites

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These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

In-Depth Information

  • Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
  • PubMed is a searchable database of medical literature and lists journal articles that discuss IQSEC2. Click on the link to view a sample search on this topic.


  1. Alexander-Bloch AF, McDougle CJ, Ullman Z & Sweetser DA. IQSEC2 and X-linked syndromal intellectual disability. Psychiatr Genet. June 2016; 26(3):101-108. https://www.ncbi.nlm.nih.gov/pubmed/27010919.
  2. Gandomi SK, Farwell Gonzalez KD, Parra M et al. Diagnostic exome sequencing identifies two novel IQSEC2 mutations associated with X-linked intellectual disability with seizures: implications for genetic counseling and clinical diagnosis. J Genet Couns. June 2014; 23(3):289-298. https://www.ncbi.nlm.nih.gov/pubmed/24306141.
  3. Tran Mau-Them F, Willems M, Albrecht B, et al. Expanding the phenotype of IQSEC2 mutations: truncating mutations in severe intellectual disability. European Journal of Human Genetics. 2014; 22(2):289-292. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3895633/.
  4. Zerem A, Haginoya K, Lev, D. et al. The molecular and phenotypic spectrum of IQSEC2-related epilepsy. Epilepsia. 2016; 57:1858-1869. https://www.ncbi.nlm.nih.gov/pubmed/27665735.