Children who are born with a single functioning copy of the SCN2A gene develop a condition called SCN2A haploinsufficiency, one of the most frequent causes of neurodevelopmental disorders. Patients with the condition have defects in the connections between some brain cells and experience symptoms such as seizures and speaking difficulties. Now, scientists from the University of California, San Francisco (UCSF), and their collaborators elsewhere are assessing whether they can use CRISPR technology to address some of the features of the disease.
Details of their preclinical work in mice engineered to carry the form of the mutation found in humans are published in a new Nature paper titled “CRISPR activation for SCN2A-related neurodevelopmental disorders.” In it, the scientists explain that rather than trying to edit the defective copy of SCN2A, they used CRISPR activation (CRISPRa) technology to up the expression of the functional one. The procedure, they reported, worked in mice that were about the same age as 10-year-old children. It suggests that young brains could still respond to treatment even after most development has been completed.
“We were surprised to see that the anatomy of the brain is totally intact—the synapses are there, but they fail to mature—when there isn’t enough SCN2A,” said Kevin Bender, PhD, a professor in the UCSF Weill Institute for Neurosciences and co-senior author of the study. “By ramping up SCN2A levels in the brain, we brought those synapses online and restored signaling that prevented seizures.”
Bender’s laboratory is responsible for one of the key discoveries underpinning the current study. Last year, his team found that a disrupted reflex identified in SCN2A mice mapped to humans. Specifically, children with a variant of SCN2A that is associated with severe autism had an unusual form of an eye reflex called the vestibulo-occular reflex (VOR). This reflex stabilizes the gaze when the head is moving. Children with autism have a hypersensitive VOR compared to neurotypical children. Scientists in Bender’s lab were able to tell which children had autism by measuring and tracking the movement of their eyes during head movements. In addition, the scientists also found that mice with this condition were more prone to seizures and altered brain signals.
The findings meant that the scientists could use mouse models of SCN2A deficiency to test possible therapeutic approaches. To that end, Bender’s lab worked with collaborators in the laboratory of Nadav Ahituv, PhD, director of the UCSF Institute for Human Genetics and a professor of bioengineering at the university, who designed the CRISPRa needed to double the expression of the healthy copy of SCN2A.
When they tested the CRISPRa intervention in mice, they saw higher levels of SCN2A throughout the brain, including normal amounts of the protein in nerve cells. Further, the added protein improved existing neural connections in the mice as well as normal brain signals. The treated mice were also no longer prone to seizures. The intervention worked both when the CRISPRa was introduced directly to the brain and also when it was injected into the blood, according to the team.
The scientists also tested the treatment in mice with two functioning copies of SCN2A and found that having extra protein present did not appear to harm them. While those results are encouraging, additional testing is needed before a therapy like this could be used in human children. “Too much of any protein might cause a lot of trouble,” Ahituv said. “We found that there is a natural limit to levels of this protein in SCN2A mice, but future therapies will need to confirm the safety of the approach in humans.”
Regel Therapeutics, a biotech company developing precision therapeutics using its so-called Targeted EpiEditing platform, has licensed this technology from UCSF to develop treatments for patients with SCN2A haploinsufficiency disorders.
