An estimated 100,000 people in the U.S. have RP, mainly caused by mutated genes inherited from one or both parents. Mutated genes give the wrong instructions to photoreceptor cells, telling them to make an incorrect protein, or too little or too much protein. (Cells need the proper amount of particular proteins in order to function properly.) Many different gene mutations exist in RP. In Usher syndrome, for example, at least 14 disease-causing genes have been identified.
Genetic mutations can be passed from parent to offspring through one of three genetic inheritance patterns – autosomal recessive, autosomal dominant, or X-linked. In autosomal recessive RP, parents who carry the gene but have no symptoms themselves could have some children who are affected and others who are not. Similarly, in autosomal dominant RP, an affected parent could have affected and unaffected children. In families with X-linked RP, only males are affected; females carry the genetic trait but do not experience serious vision loss.
If a family member is diagnosed with RP, it is strongly advised that other members of the family also have an eye exam by a physician who is specially trained to detect and treat retinal degenerative disorders. Discussing inheritance patterns and family planning with a genetic counselor can also be useful.