Daniel de Boer, Founder and CEO of ProQR, discussuses Usher syndrome, a genetic disorder characterized by sensorineural hearing loss or deafness and progressive vision loss due to retinitis pigmentosa. Sensorineural hearing means it is caused by abnormalities of the inner ear. Retinitis pigmentosa is an eye disease that affects the layer of light-sensitive tissue at the back of the eye (the retina). Vision loss occurs as the light-sensing cells of the retina gradually deteriorate. Night vision loss begins first, followed by blind spots that develop in the side (peripheral) vision, that can enlarge and merge to produce tunnel vision (loss of all peripheral vision). In some cases, vision is further impaired by clouding of the lens of the eye (cataracts).
Three major types of Usher syndrome have been described – types I, II, and III. The different types are distinguished by their severity and the age when signs and symptoms appear. All three types are inherited in an autosomal recessive manner. Treatment for the hearing loss may include hearing aids or surgery for a cochlear implant. Vitamin A palmitate is useful for treating the vision loss in people with Usher syndrome type II.
USH2 is most commonly caused by mutations (or mistakes) in a gene in the DNA called the USH2A gene. This gene is responsible for the formation of the usherin protein. The mutation results in a lack of (functional) usherin protein and disrupts a process called photo transduction in the light detecting cells (rods and cones) in the retina causing RP.