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Retinitis Pigmentosa

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Overview

Retinitis pigmentosa (RP) describes a group of genetic disorders that damage light-sensitive cells in the retina, leading to gradual vision loss over time as the cells die off. While the condition is classified as a “rare disease,” it is one of the most common inherited diseases of the retina, affecting between 1 in 3500 to 1 in 4000 Canadians.[1] RP is often referred to as an inherited retinal disease, meaning that it is passed along genetic lines and inherited from one’s parents. Though it is usually diagnosed during childhood or adolescence, a minority of patients report symptoms later in life.

Specialized cells called photoreceptors are responsible for absorbing light and translating it into signals that are interpreted by the brain—it is these essential cells that gradually die off as a result of RP. The cells come in two varieties: rod cells and cone cells. Rod photoreceptors are responsible for peripheral and night vision, while cone photoreceptors are responsible for central, high-acuity vision as well as detail and colour. Since it is the rod cells that are first damaged by RP, peripheral and night vision are affected during the early stages of the disease, followed by a narrowing of the visual field, often referred to as a progressive form of “tunnel vision.” The death of rod cells eventually affects the cone cells as well, leading to the loss of central vision and often resulting, during the later stages of the disease, in near or total blindness. The length of this process varies from individual to individual.

A cross-section of the retina showing its different layers. The rod and cone photoreceptors can be seen at the top of the magnified section. Image taken from the National Center for Biotechnology Information.

RP was originally considered a single disease, but after decades of research—including research funded by FBC—we now know that there are several forms of RP, and that these forms involve mutations in any one of more than 64 different genes. The gene or genes affected determine the disease type and symptoms.

There are several different ways that RP can be inherited, which is usually described as the “inheritance pattern.” The different RP inheritance patterns include: autosomal dominant, autosomal recessive, and x-linked recessive. A genetic counsellor can talk with you about your family history and determine which of these patterns is associated with your vision loss. With this information, the genetic counsellor may be able to tell you more about how your condition will progress, and give you and your family information about the risks of vision loss for other family members. To learn more about genetic testing for RP, please consult our Genetic Testing Primer.

Typically, each person with RP only has damage in one pair of genes. Scientists have now identified more than 64 genes that can have mutations that cause RP. It is likely that mutations in more than 100 different genes will eventually be identified. Because so many RP-causing gene mutations are still unknown, there is about a 50:50 chance that genetic testing will provide a definitive result. Given your family history and the inheritance pattern of your RP, your genetic counsellor will be able to advise you about the likelihood that a genetic test will provide a definitive result.

Different genetic mutations can damage the retina or impair its function in different ways; for example, some mutations affect how the retina processes nutrients, while others damage the photoreceptors. It’s important to identify the specific gene and mutation, because many treatments being developed for RP will be for particular genetic types.

Content on this page was written by Dr. Chad Andrews and Dr. Mary Sunderland, and was most recently updated on August 23, 2018. An earlier version of the content was approved by Dr. Jane Green and Dr. Bill Stell.

tELL uS wHAT IT’S lIKE TO lIVE wITH rp

Fighting Blindness Canada is undertaking a study about how RP affects peoples’ daily lives. Share your experience and support our efforts to give Canadians access to the latest treatments for RP by filling out the survey below.

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