August 27, 2025 

Andrew P.  Levy MD PHD 

 IQSEC2 is a protein which is critical for normal brain development.  Without a properly functioning IQSEC2 molecule children will develop seizures, poor language skills, and a moderate to severe learning disability.  All children with IQSEC2 disease have a change in their DNA (mutation). We and our collaborators have created mice with the same DNA mutations found in children with IQSEC2 disease.  These mice display seizures, behavioral changes, and learning disabilities similar to children with IQSEC2 disease.      

In this research study we set out to test whether providing a normal copy of the IQSEC2 DNA could prevent or rescue mutant mice from developing the disease.  We introduced the IQSEC2 DNA using a special type of virus which doesn’t infect people (adeno associated virus).   We also used genetic methods to make sure IQSEC2 would only be made in the brain.  

After the mice received the virus we monitored their growth, seizure activity, and behavior.   In all cases we were able to demonstrate that mice that received the virus had a dramatically improved condition.   The treated mice grew to be larger, had fewer seizures, and showed improved social behavior.  

Another important finding in the study was that treated adult mice, not just young mice, showed improvement.  This suggests that the window for this type of therapy may be quite broad, allowing teenagers or young adults with IQSEC2 mutations to be helped.  

One of the most important aspects of this study is that it was done in three different laboratories, increasing the reliability and confidence of the generated data. 

This does not represent a cure for IQSEC2 disease.  It does, however, represent a major step forward in providing a treatment that could significantly improve the lives of many children with IQSEC2 disease.   Our next step is to carry out a clinical trial within the next year which will depend on fund raising and regulatory compliance to make sure the study is done safely.  Our goal is to make treatment available to all children with IQSEC2. More details will be discussed in an upcoming webinar for the IQSEC2 community.

The research projects selected for funding were selected based on their ability to develop new therapeutics for treating our children with IQSEC2 mutations. Each project is funded for one year. 

The project let by Dr Cheryl Shoubridge will be generating brain cortical neurons derived by genetic reprogramming of skin cells taken from children with three different IQSEC2 mutations. It is known that cortical neurons from mice with IQSEC2 mutations display abnormalities in the way they can spontaneously discharge (the in vitro correlate of a seizure). This study will compare how neurons from children with IQSEC2 human mutations may differ in this abnormality and will allow the assessment of multiple anti-epileptic drugs on their ability to restore the normal electrical activity of the cells and may suggest which drugs would be best for which IQSEC2 mutations. As many parents with children with IQSEC2 mutations know, the search for an epilepsy drug is generally done by trial and error on the child with some children needing to go thru 10-20 medications. This would represent a personalized approach to the epilepsy treatment of children with IQSEC2 mutations and allow mixing and matching of multiple different treatments to help find the optimal approach for a given child’s mutation.  

The project led by Dr Takuma Mori will be to design a female model of IQSEC2 mutation associated disorders in mice. Virtually all IQSEC2 research to this point has been done in male mouse disease models. As the IQSEC2 gene is on the X chromosome, males have only one copy of the IQSEC2 gene and females have two copies. In general one of the two X chromosomes is inactivated in a cell in females and this is generally random so that if a female had one mutated copy of a gene on the X chromosome and one normal copy of the gene on the other X chromosome half of the cells would express only the mutated copy and half would express the normal copy.   In mice, this is indeed how the IQSEC2 gene is regulated on the mouse X chromosome (X inactivation). However, in humans it appears that IQSEC2 at least partially escapes X inactivation- the inactivation is skewed and both copies of the IQSEC2 gene may be expressed in a given cell. This means that currently available mouse models of IQSEC2 mutations may not mimic what is going on in female IQSEC2 patients. Dr Mori will be developing a model to introduce heterogeneity (resulting in variable degrees of IQSEC2 dysfunction) between neurons in IQSEC2 expression in the mouse brain similar to what occurs in human female brains and assessing how this heterogeneity influences disease in the mice. Furthermore, Dr Mori will assess the ability of viral mediated gene therapy to rescue abnormalities in this female model of IQSEC2 disease in the mice.  

The project led by Dr Sahar Daas will be to develop a zebrafish model of the IQSEC2 mutation.  The IQSEC2 gene is remarkably conserved in its structure and function in every known vertebrate organism. The zebrafish is a model organism that is transparent allowing one to visualize the development of the nervous system in a living animal. Furthermore, zebrafish have been used to study seizures, neurodevelopment, behavior and learning. Dr Daas and his group will first eliminate the expression of IQSEC2 from the zebrafish and then will study how this influences development, seizures and learning.  The zebrafish with IQSEC2 mutations will  then be used as a high throughput system for screening small molecules (drugs) that can block seizures and allow more normal development in these organisms.    The zebrafish has been used in a similar capacity to identify drugs to treat other genetic epilepsy conditions (i.e. Dravet Syndrome).

The project led by Dr Donald Joseph will investigate the abnormal neural circuits, which exist in a mouse model of IQSEC2 mutation in which the mice have seizures. The triggers for the start of the seizures and how the seizures propagate in the brain will be investigated. This basic mechanistic understanding of how IQSEC2 seizures are generated is critical for the development of new treatments to prevent these seizures. Dr Joseph will may use this system to assess the efficacy of new treatments (small molecules or viral gene therapy) to restore the normal neural networks and prevent seizures. Theoretically, this model may also allow for the ability to change abnormal neural circuits associated with IQSEC2 mutations and the developmental time window during which this change may be possible.

The first gene therapy trials in three distinct laboratories are underway using the IQSEC2 minigene

Adeno-associated virus (AAV) has recently been demonstrated to successfully deliver a replacement copy of a defective gene for several diseases in humans. The FDA, the major licensing body in the USA that has been given the task of ensuring that new therapeutics are safe and effective, has approved the use of AAV in humans. There are now many clinical trials underway for other genetic diseases.

Applying AAV to deliver a “good” copy of the gene, as we wrote in October, has two major hurdles for a given gene. First, the way that we deliver gene therapy with AAV is by replacing the genes that normally appear in the virus with our gene of interest (in our case IQSEC2). The problem is that the size of the gene that can fit in the AAV has to be small and over half of all genes are too big. IQSEC2 is way too big to fit in an AAV. The second problem is providing specificity for where the gene is delivered and how it gets into the brain.

The IQSEC2 gene is only used in brain neurons and getting into the brain is challenging due to the existence of a barrier between the rest of the body and the brain (known as the blood brain barrier or BBB). The purpose of the BBB is to block the ability of molecules that get into our blood from our diet, or from other entry points, from getting into the brain.

Over the past few months we have surmounted these problems. First, we have found a way to reduce the size of the IQSEC2 gene so that it can fit within the AAV virus. This has entailed reducing the size of the IQSEC2 gene by over 40%. This was possible based on our ability to model the molecular structure of the protein made by the IQSEC2 gene (see our new paper in Journal of Biomolecular Structure and Dynamics). We were then able to identify regions in the IQSEC2 protein which were not important in its function per se; rather their function was merely to connect functional regions of the protein. An appropriate analogy might be when you look at a map of a country you see big cities connected by lines (highways). The cities provide the function to the country: factories, major places of employment, services, whereas the highways serve to connect the cities. Each city has its own function and together the network of highways serves to connect all the functions to work together. All of the reduction in IQSEC2 which we have achieved has been in its highways or connectors between the functional domains of IQSEC2. We have created a new way to reconnect the domains using a very short stretch of the simplest amino acid glycine. We have studied this miniature IQSEC2 (hereafter referred to as miniIQSEC2) in terms of its function in a virtual and experimental setting and found that the miniIQSEC2 gene is similar, if not identical, to the normally existing IQSEC2 gene in terms of the protein that is produced and its functionality in multiple different measurements.

The second problem – one of specificity – has been surmounted by inserting control regions in front of the IQSEC2 gene that will only allow it to be made in neurons. Finally, the ability of the AAV to cross the BBB has been recently been shown to be possible.

Therefore, we are excited to say that the first gene therapy trials in three distinct laboratories are underway using the IQSEC2 minigene. All three labs will be using the same AAV construct to see if it can prevent IQSEC2 disease in mice with different IQSEC2 mutations. These experiments will be examining the ability of the AAV with the IQSEC2 minigene to prevent seizures, to improve learning, and to correct abnormalities in behavior (including speech). In science it is extremely important to show that results are reproducible and thus having three different labs working on the same problems will be extremely helpful in providing confidence that the approach will work. We are hoping to know by this fall if the AAV with the IQSEC2 minigene is effective.

This is a major step forward. We are hopeful, but also realistic, that the AAV we create may need to be refined and may only be effective for a subset of IQSEC2 mutations. However, the current studies underway are the translational bridge for our previous basic science studies and the establishment of clinical trials in children with IQSEC2 disease.

If we are able to demonstrate benefit with the IQSEC2 minigene AAV our next step would be in clinical trials. We hope to come back to you soon with an update!

Andy Levy
Technion Israel Institute of Technology
Haifa, Israel