Usher syndrome is a rare genetic disorder that is characterized by deafness and often paired with retinitis pigmentosa (RP), an inherited disease which causes retinal degeneration and vision loss. There are different subtypes of Usher syndrome. For example, type 1F is characterized by profound hearing loss at birth and progressive vision loss beginning in adolescence. Additional symptoms include severe balance issues, cataracts, or sitting or walking independently later than other children.
Right now, Usher syndrome treatments address the disorder’s symptoms rather than its underlying causes. But, shares an article in Medical XPress, a research team comprising members from Ohio State University, Harvard Medical School, and Massachusetts Eye and Ear are working to develop a gene therapy that could treat Usher syndrome type 1F at its source.
Unpacking the Usher Syndrome Research Findings
PCDH15 gene mutations cause Usher syndrome type 1F. This gene encodes for the production of a protein called protocadherin-15. Prior research found that protocadherin-15 plays a role in auditory and visual function. In terms of hearing, the protein partners with a protein called cadherin 23; this partnership opens ion channels and allows electrical current to enter hair cells (a type of sensory receptor) in the ear. These help the brain to identify sound. A slightly modified version of protocadherin-15 is found in the eye to assist with sight.
In this research, published in Nature Communications, the researchers began by developing a shortened version of PCDH15, which they called a “mini gene.” They created 8 versions of the mini gene, then tested them on inner ear cells. The researchers found that protocadherin-15 and cadherin 23 could still bind. They then identified 3 versions that they felt would be most successful and tested these on mice models of Usher syndrome type 1F.
Only one mini gene successfully treated the mice models. After treating the mice with this particular mini gene, the proteins banded together. The hair cells in the ears began working correctly. As a result, the mice—who had profound deafness—were now able to hear.
In humans, we may not see the same results, the researchers warn. Because children with this condition are born with profound hearing loss, they may not have the hair cells necessary to have these results. However, the researchers believe that they can use this approach and what they have learned to stop vision loss and retinal degeneration. The research team is now testing this approach on zebrafish models. If effective, they hope to continue testing and eventually evaluate the therapy in people.