Genetic Treatments for Autism Spectrum Disorder: The Example of a Single Gene Disorder, Angelman Syndrome

Ben Philpot, Ph.D. - Neuroscience Center, Carolina Institute for Developmental Disabilities, Autism Research Center, Department of Cell Biology and Physiology at UNC Chapel Hill.

Sponsored research agreements with various pharmaceutical companies and Biotech companies

Background

Most neurological disorders have a genetic basis and disorders are oftentimes caused by genetic mutations. The human genome has about 25,000 genes and we each have about 60 mutations within out genome. All of these genes makeup the blueprint for our body, coding for proteins which allow us to function properly.

Example: collagen is a protein that is important for the health of joints and ligaments. If there were a mutation that disrupted collagen production we would have issues with our joints and their ability to function properly. Most neurological disorders are caused by multiple genetic mutations combined. There are some neurological disorders that result from a single gene mutation. Angelman Syndrome is one of these disorders, and this is what is studied in the following research.

Angelman Syndrome overview

Symptoms

Frequent laughter and smiling. THese individuals are very endearing and happy individuals but face many challenges
Movement or balance disorder
Severe developmental delay
Severe speech impairment, some may be nonverbal
90% have seizures
80% have rhythmic EEG patterns
About 75% have sleeping disorders.

Caused by a single gene deletion. The deleted gene is UBE3A and results in the expression of Angelman Syndrome

Prevalence is 1 in 20,000

There is a high presence of ASD comorbidity

Extra copies of the UBE3A gene are linked to the expression of ASD.
- ASD has a prevalence of 1 in 59

Quick Genetics 101

You inherit genes from both the mother and the father, allowing you to have two copies of each gene.

Therefore you have two copies of the UBE3A gene, however the UBE3A gene in the paternal strand of DNA is silent because there is another gene that silences UBE3A inorder to form proteins… This is a neurotypical occurrence

The presence of the UBE3A gene in the maternal DNA is the determining factor of whether or not an individual will have Angelmans Syndrome

Because the presence of Angelmans Syndrome is dependent on a single gene from one strand of DNA it is vulnerable to “genetic distractions”

Angelman Syndrome occurs when:

An individual does not express the UBE3A gene inherited from the mother
Or when a mutation occurs causing the deletion of the gene

The absence of the UBE3A gene prevents the creation of a protein that is important for neurotypical brain functioning

Studying Angelman syndrome in mice

When the UBE3A gene is deleted in mice they experience the same impairments as a child with the disorder.
- Memory impairments
- Movement impairments
When looking at a slice of cerebellum in mice stained for the protein created by UBE3A:
- A neurotypical brain will light up green due to the presence of the protein
- The brain with Angelman syndrome will not light up at all.
Desired outcome from Angelman treatment: Restore the proper functioning of the UBE3A gene so that the proteins can be properly made.
- This should be able to improve things like memory, speech, movement, and decrease seizures

Treatment

Two ways to restore proper gene functioning:

#1: The Gene Activation Strategy

Treating individuals with angelman syndrome with a small molecule drug that will turn off the STOP code on the gene that silences UBE3A in the paternal DNA
Topoisomerase inhibitors were found to unsilence the UBE3A in neurons in vitro
- This drug is already FDA approved for cancer treatments
- The drug is inserted into the spinal cord of mice and can successfully unsilence paternal UBE3A
- The mice took treatments for two weeks and were analyzed a year after their last treatment and the UBE3A gene seemed to still be unsilenced and producing the necessary proteins.

Complications of the drug:

They do not know the mechanism that allows the drug to work
It needs to have improved brain delivery
It needs to be made out of safer compounds that will not result in negative side effects similar to those of individuals going through chemotherapy.

#2: Direct Gene Therapy

Take a virus and genetically modify it so that it no longer has the negative side effects of a typical virus. Instead, give it the information that it needs to code for the production of the desired protein.
These treatments can be directly injected into the brain, through an IV or intrathecal injection.
When The gene therapy was injected into mice brains they were able to properly code for the missing protein in individuals with angelman syndrome
- This significantly decreases the severe and life threatening symptoms of an individual with angelman syndrome

Complications:

This form of gene therapy is permanent and not enough research has yet gone into the long term impact of this form of gene therapy