Usher syndrome

Usher syndrome affects two senses at once: hearing and vision. The vision loss gets worse over the years. The deafness is sensorineural, meaning the problem is not that sound fails to get through, but that something is wrong in the inner ear, which is where sound is turned into a nerve signal.

The vision loss has a name of its own: retinitis pigmentosa, a disease of the retina, the light-sensitive layer of tissue at the back of the eye. Behind all of it are mutations, errors in the genetic instructions the body is built from, and the same defect wears down two different systems: the one that hears and the one that sees. With most of those mutations, the inner ear loses its hair cells, the cells that turn sound into signals for the brain; in the retina, by contrast, the loss is gradual: the rods and cones, the two cell types that detect light, disappear.

Three main types have been identified, I through III, and all three are inherited in an autosomal recessive pattern, the form of inheritance in which both copies of the gene have to be altered. Among all the causes of deafblindness, this syndrome accounts for half of the cases.