The vision loss associated with Usher syndrome (USH) is caused by retinitis pigmentosa (RP), regardless of the underlying gene mutation. The gene mutations initially affect the rod photoreceptors, leading to symptoms of night blindness. In the later stages of RP, there is a decline in central vision indicating damage to the cone photoreceptors. This paper explores the relationship between cone degeneration and rod demise. The researchers found that death of rod cells causes subsequent glucose starvation in cone cells. Depriving the cone photoreceptors of glucose led to loss of structural and functional characteristics, called “cone dormancy,” and dormant cones were reactivated by subretinal injections of glucose.
What this means for Usher syndrome: Therapeutic treatments that prevent the dysfunctional death of rod photoreceptors may allow them to preserve their secondary cone preservation function of providing glucose. If so, then functional vision may be maintained until more definitive treatment measures become readily available.