Retinitis pigmentosa

Retinitis pigmentosa (RP) can be inherited in an autosomal dominant, autosomal recessive, or X-linked manner. The mode of inheritance in a particular family is determined by evaluating the family history and, in some instances, by molecular genetic testing. There are many potential complications in interpreting the family history, so in some cases, identifying the responsible gene with genetic testing is needed.

• Autosomal dominant inheritance means that having a change (mutation) in only one copy of the responsible gene in each cell is enough to cause features of the condition. In some cases, an affected person inherits the mutated gene from an affected parent. In other cases, the mutation occurs for the first time in a person with no family history of the condition. When a person with a mutation that causes an autosomal dominant condition has children, each child has a 50% chance to inherit that mutation.
• Autosomal recessive inheritance means that to be affected, a person must have a mutation in both copies of the responsible gene in each cell. Affected people inherit one mutated copy of the gene from each parent, who is referred to as a carrier. Carriers of an autosomal recessive condition typically are unaffected. When 2 carriers of an autosomal recessive condition have children, each child has a:
  • 25% chance to be affected
  • 50% chance to be an unaffected carrier like each parent
  • 25% chance to be unaffected and not a carrier
• X-linked inheritance means that the responsible gene is located on the X chromosome. Males have one X chromosome (and one Y chromosome), while females have two X chromosomes. Males who have a mutation on their X chromosome will be affected, while female carriers of the mutation may be affected or unaffected, because they have another X chromosome with a normal copy of the gene.
  • All the daughters of an affected male will inherit the mutation; none of his sons will inherit the mutation.
  • The sons of a female with a mutation have a 50% chance to inherit the mutation and be affected; the daughters have a 50% chance to inherit the mutation (and be affected or unaffected).

The prevalence of retinitis pigmentosa in the United States is estimated to be between 1 in 3,500 to 1 in 4,000 individuals.

Available treatments aim to slow the progression of the disease and primarily include light avoidance and the use of low-vision aids. Some practitioners also consider vitamin A as a possible treatment option. However, taking too much vitamin A can be toxic and the effects of vitamin A on the disease appear to be relatively weak. Studies have explored potential treatment with DHA, an omega-3 fatty acid naturally found in fish. While DHA is known to play a structural role in retinal cells, more research is needed to determine whether supplements should be recommended.

Current research is focused on the development of new treatments including gene therapy, retinal transplantation, and the use of a retinal prosthesis. Stem cell transplantation would involve the injection and integration of stem cells into the retina, in hopes these cells will replace dead cells and provide the missing enzymes and chemicals needed for sight. Gene therapy could potentially be used when the disease-causing mutation is known and would aim to restore production of the missing or abnormal protein. Studies with retinal prosthetics have tested devices that transform light into electrical signals that can be sent directly to the inner retina and brain, avoiding the diseased part of the outer retina. Though challenges remain, preliminary research into these technologies has been promising.