Retinitis pigmentosa is an inherited disorder, and therefore not caused by injury, infection or any other external or environmental
factors. People suffering from RP are born with the disorder already programmed into their cells. Doctors can see the first
signs of retinitis pigmentosa in affected children as early as age 10. Research suggests that several different types of gene
mutations (changes in genes) can send faulty messages to the retinal cells which leads to their progressive degeneration.
In most cases, the disorder is linked to a recessive gene, a gene that must be inherited from both parents in order to cause
the disease. But dominant genes and genes on the X chromosome also have been linked to retinitis pigmentosa. In these cases,
only one parent has passed the disease gene. In some cases, a new mutation causes the disease to occur in a person who does
not have a family history of the disease. The disorder also can show up as part of other syndromes, such as Bassen-Kornzweig
disease or Kearns-Sayre syndrome.
What do we know about heredity and Retinitis Pigmentosa?
Since RP is an inherited disorder, it can potentially affect another member of the family. With retinal cells being among
the most specialized cells in the human body, they depend on a number of unique genes to create vision. A disease-causing
mutation in any one of these genes can lead to vision loss. Researchers have discovered over 100 genes that can contain mutations
leading to retinitis pigmentosa. Approximately 50 percent of RP cases are isolated and have no previous family history. The
cause of these cases cannot be explained. Other cases of RP, where family history has been determined, fall into three main
categories: autosomal recessive, autosomal dominant, and X-linked recessive.
Autosomal recessive RP occurs when both parents are unaffected carriers of the same defective gene. The chances of a child
being affected is one in four. This means the affected child must inherit the defective gene from each parent. The chances
of a parent having an unaffected child who would be a carrier of the defective gene is one in two. The chance of parents having
a child completely free of the RP gene is one in four.
In autosomal dominant RP, the disease is present in males or females only when a single copy of the gene is defective.
Typically, one of the parents is affected by the disease. The chance is one in two of any given offspring being affected by
the disease, if the affected parent has one normal and one defective gene.
X-linked recessive RP may occur in offspring in two ways. The fathers can be affected or mothers can be carriers of the
defective gene. If the father is affected, all sons will be unaffected and all daughters will be carriers. If the mother is
the carrier, 1 in 2 sons will be affected and 1 in 2 daughters will be carriers. In families with the X-linked type, only
males are affected, while females carry the genetic trait but do not experience serious vision loss.