What is an IQSEC2-related disorder?
IQSEC2 plays an important role in brain development and function. Changes in the IQSEC2 gene, which alter the gene’s ability to function, result in IQSEC2-related disorder.
What are the health implications associated with a disease-causing change in the IQSEC2 gene?
All males with IQSEC2-related disorder have some degree of intellectual disability, some will also have autism and/or seizure disorders (epilepsy or fits).
The effect of an IQSEC2 gene change on females is variable, ranging from no affect to severe disability. Some of this variation may depend on how badly the gene’s function has been affected.
Only a small number of individuals and families around the world have been found with IQSEC2-related disorder, therefore we are still learning more about this condition.
How is an IQSEC2-related disorder inherited?
Some individuals with an IQSEC2-related disorder come from families with a family history of intellectual disability, behavioural and mental health conditions and/or seizures. Other individuals have no family history.
The IQSEC2 gene is located on the X chromosome. Therefore, the pattern of inheritance is referred to as X-linked inheritance.
Males inherit an X chromosome from their mother and a Y chromosome from their father. Males who inherit an X chromosome with a change in the IQSEC2 gene, which can’t work properly, will have IQSEC2-related disorder.
Females have two X chromosomes: one inherited from their mother and one from their father. Both of these X chromosomes carry an IQSEC2 gene. Females with a gene change in one of their IQSEC2 genes are called carriers. Female carriers usually do not show symptoms of IQSEC2-related disorder because they have a second working copy of the gene. However, sometimes they can be affected, if that working copy is not functioning in enough cells in the brain, or the gene change is particularly severe. It is not possible to predict before birth whether a female carrier will be affected or not.
What are the chances of a female carrier having a child with an IQSEC2-related disorder?
When a female carrier is having children, for each pregnancy, there is a 50% (1 in 2) chance of passing on the X chromosome with the working IQSEC2 gene and a 50% (1 in 2) chance of passing on the X chromosome with the IQSEC2 gene change. This means there is a 25% (1 in 4) chance of having a son with IQSEC2-related disorder and a 25% (1 in 4) chance of having a daughter who is a carrier (please see the diagram below).
Female carriers have choices when planning children, and these options can be discussed with a genetic counsellor at your Regional Medical Genetics Unit.