Gene therapy is an experimental method of using genes (the fundamental units of heredity) to prevent or treat a disease. In gene therapy, a defective gene is either inactivated or replaced with a healthy copy to slow down or halt the progression of a disease.

The therapy is still in the experimental stages, with many safety and efficacy studies required before it can be tested in clinical trials.

Gene therapy for Angelman syndrome

In Angelman syndrome, the maternal copy of the UBE3A gene (which is required for certain neurologic functions) is mutated, resulting in symptoms that include communication problems, movement and coordination issues, and scoliosis (abnormal curvature of the spine).

Gene therapy for Angelman syndrome currently focuses on introducing a healthy copy of the UBE3A gene directly into the nerve cells using a harmless adeno-associated virus (AAV).

Several gene therapy approaches are being investigated for the treatment of Angelman syndrome, and are summarized below.


AGIL-AS is an investigative gene therapy being developed by PTC Therapeutics (which acquired the therapy’s original developer, Agilis Biotherapeutics, in 2018). It uses an AAV-based approach to deliver a working copy of the UBE3A gene to the brain and spinal cord so that its protein product E6-AP — which is required for proper nervous system function — can be produced.

Preclinical studies have shown that AGIL-AS is effective in localizing to the nerve cells in the brain, increasing levels of E6-AP, and improving cognitive deficits associated with Angelman syndrome.

AGIL-AS received orphan drug designation from the U.S. Food and Drug Administration in 2015, followed by a similar designation from the European Commission in 2016.

Upcoming gene therapies

Researchers at the University of North Carolina (UNC) demonstrated the potential of gene therapy to reduce seizures in mouse models of Angelman syndrome. They found that turning on the UBE3A gene using a chemical switch was effective in preventing seizures in juvenile mice models of Angelman syndrome. However, this approach did not seem to be effective in adult mice.

Recently, UNC researchers also showed that gene therapy performed directly on the fetal brain could offer a possible one-time treatment for Angelman syndrome. They used CRISPR-Cas9 gene-editing tools directly on mouse brains in utero to switch on the paternal dormant copy of the UBE3A gene in several parts of the brain, including the cerebral cortex (which is associated with cognitive functions), hippocampus (associated with learning and memory), and cerebellum (associated with balance and movement). This approach helped in activating UBE3A gene function in these brain regions.

Follow-up studies in human nerve cells grown in the laboratory also proved to be effective. This approach could one day allow the in utero treatment of Angelman syndrome.

Safety concerns

Gene therapy, although highly promising, comes with uncertainties and therefore requires thorough safety and efficacy evaluations before it can progress into clinical trials. Some of the associated risks of gene therapy include inflammation, toxicity, and cancer.

There is also the possibility of the gene being delivered to the wrong site in the body and the uncontrollable expression of the newly inserted gene, both of which can cause serious complications.


Last updated: Sept. 10, 2019


Angelman Syndrome News is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website. 

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Özge has a MSc. in Molecular Genetics from the University of Leicester and a PhD in Developmental Biology from Queen Mary University of London. She worked as a Post-doctoral Research Associate at the University of Leicester for six years in the field of Behavioural Neurology before moving into science communication. She worked as the Research Communication Officer at a London based charity for almost two years.