Vision loss is a symptom associated with a number of disorders, one of which is Usher syndrome. Medical professionals have spent years trying to fully comprehend the underlying mechanisms of this loss, and a recent study seems to have done just that. Titled, “Proposed therapy, developed in a Pcdh15-deficient mouse, for progressive loss of vision in humans with Usher syndrome,” this study identified the cellular mechanism driving vision loss within this rare disorder, along with a possible treatment.
About Usher Syndrome
Firstly, let’s dive into what Usher syndrome is. This rare disorder is characterized by hearing and vision loss and is often accompanied by retinitis pigmentosa. There are three forms, distinguished by the symptoms’ severity and the age at which they begin. In the first form, children are born deaf in both ears with vision problems, and they begin to lose their vision around age ten. The second form sees progressive hearing loss beginning at birth, which is joined by progressive vision loss in the teens or 20’s. Lastly, the third form sees hearing loss, vision loss, and balance problems all begin in the third or fourth decade of life.
In terms of causes, Usher syndrome is a genetic disorder that is passed down in an autosomal recessive pattern. At least ten genes have been identified in connection with this condition, including MYO7A (USH1B), USH1C, CDH23, PCDH15 (USH1F), SANS (USH1G), USH2A, ADGRV1, WHRN, USH3A, and HARS. Regardless of which genetic mutation one has, treatment is symptomatic. Hearing aids, cochlear implants, and visual aids may all be helpful.
About the Research
This research looks specifically at Usher syndrome type 1F (USH1F), a disorder that disproportionately affects the Ashkenazi Jewish population. In terms of prior research into this condition, there is minimal. A study from 2000 discovered that half of its participants with USH1F had lost their vision to the point of legal blindness by age 50 and identified the key mutation in the PCDH15 gene, but other than that, scientists remained largely in the dark when it came to this form of Usher syndrome.
Armed with the knowledge of the PCDH15 gene, the researchers created a mouse model of Usher syndrome with this mutation. As in humans, the mouse with this alteration produced a shorter version of the protocadherin-15 protein. However, the researchers were unsure as to how this change led to the characteristic vision loss seen in Usher syndrome.
Using healthy mice as a control, the team found two purposes of this protein:
- It plays a role in moving light-dark cycle proteins back and forth between the photoreceptors of the eyes
- It is necessary to help recycle retinoids
After discovering this information, the researchers decided to administer retinoid injections to the affected mice to see if it would combat vision loss. They found increased electrical activity after the injections, pointing to improvements in vision.
While these drugs will not be a cure, they point to a way to slow the vision loss that accompanies Usher syndrome. Similar drugs have already been approved by the FDA, and others will hopefully enter the clinical trial space to treat Usher syndrome.
You can find the source article here.