Gene Therapy Could Restore Function in Angelman Syndrome Patients

Scientists at the UNC School of Medicine have shown that gene editing and gene therapy techniques can be used to restore UBE3A in human neuron cultures and treat deficits in an animal model of Angelman syndrome. The study was published today in Nature.

"Our study shows how multiple symptoms associated with Angelman syndrome could be treated with a CRISPR-Cas9 gene therapy," senior author Mark Zylka said. "And we are now pursuing this with the help of clinicians at UNC-Chapel Hill."

Angelman syndrome is caused by a deletion or mutation of the maternal copy of the gene that encodes the ubiquitin protein ligase E3A (UBE3A). The paternal copy of UBE3A is typically silenced in neurons, so the loss of maternal UBE3A results in a complete absence of the UBE3A enzyme in most areas of the brain. That's crucial because the enzyme targets proteins for degradation, a process that maintains normal function of brain cells. When that process goes awry, the result is Angelman syndrome, a brain disorder with symptoms that include severe intellectual and developmental disabilities, seizures, and problems with speech, balance, movement, and sleep.

"Turning on the paternal copy of UBE3A is an attractive therapeutic strategy because it could reverse the underlying molecular deficiency of the disease," Zylka said. However, the paternal gene is silenced by a long strand of RNA, produced in the antisense orientation to UBE3A, which blocks production of the enzyme from the paternal copy of the gene.

The team set out to devise a way to use CRISPR-Cas9 to restore the UBE3A enzyme to normal levels by disrupting the antisense RNA. Preliminary data in cell cultures were promising, and Zylka received grants from the NIH, the Angelman Syndrome Foundation, and the Simons Foundation to test their findings in human neurons and in a mouse model of the disease. They used an adeno-associated virus (AAV) gene therapy to deliver the Cas9 protein throughout the brain of embryonic mice that model Angelman syndrome. Because UBE3A is essential for normal brain development, early treatment is crucial. The researchers found that embryonic and early postnatal treatment rescued physical and behavioral phenotypes that model core deficits found in Angelman syndrome patients. Remarkably, a single neonatal injection of AAV unsilenced paternal Ube3a for at least 17 months, and the data suggest this effect is likely to be permanent. The researchers also demonstrated that this approach was effective in human neurons in culture.

"We were blown away when we got these results," Zylka said. "No other treatments currently being pursued for Angelman syndrome last this long, nor do they treat as many symptoms. I am confident others will eventually recognize the advantages of detecting the mutation that causes Angelman syndrome prenatally and treating shortly thereafter."