'Retinitis Pigmentosa (RP),' refers to a group of inherited diseases that cause retinal degeneration in a person's eyes. The cell-rich retina lines the back inside wall of a person's eye. It is responsible for capturing images from the person's visual field. People with RP experience a gradual decline in their vision because, 'photoreceptor,' cells or, 'rods and cones,' die. Forms of RP and related diseases include Leber's congenital amaurosis, Usher syndrome, Bardet-Biedl syndrome, rod-cone disease, and Refsum disease.
Causes of Retinitis Pigmentosa
Instead of being considered a single disease, retinitis pigmentosa (RP) is perceived as a group of diseases that affect how light-sensitive cells in the back of a person's eye function. Not very much is known about what causes RP except that the disease is inherited. Retinitis pigmentosa causes light-sensitive cells in the back of a person's eye to deteriorate, often times leading to gradual blindness.
Medical science has discovered that the eye condition is associated with at least 32 different genes which control traits that are passed on in a variety of different ways. At times, the genetic trait is dominant and likely to be passed on to a child when a parent has the disease. At other times, the trait for RP is recessive and might be present for a number of generations before it appears in a member of a family.
What this means is that even if your father or mother do not have retinitis pigmentosa, you might still have the eye disease if at least one of your parents carries an altered gene that is associated with the trait. Approximately 1% of the population may be considered to be carriers of genetic tendencies for retinitis pigmentosa (RP). The disease occurs in around 1 out of every 4,000 people in the United States of America. When the trait is dominant it is more likely to appear when people are in their 40's. When the trait is recessive, RP tends to first appear when a person is in their 20's.
Symptoms of Retinitis Pigmentosa
The symptoms of RP depend on whether a person's rods or cones are initially involved. In most forms of RP, a person's rods are affected first. Due to the fact that rods are concentrated in the outer portions of a person's retina and are triggered by dim light, their degeneration affects both night and peripheral vision. When the more centrally located cones, which are responsible for sharp and color central vision become involved, the loss is in central vision and color perception.
One of the earliest and most common symptoms of RP is night blindness. People with mainly cone degeneration; however, first experience decreased central vision and ability to discriminate color.
Retinitis pigmentosa is usually diagnosed in adolescents and young adults and is a progressive disorder. The rate of progression and degree of visual loss differs from person to person. The majority of people with RP are legally blind by the age of 40 and experience a central visual field of less than 20 degrees in diameter. In families with X-linked RP, men are more often and more severely affected. Women carry the genetic trait and less frequently experience vision loss.
Retinitis Pigmentosa and Inheritance
An estimated 100,000 people in America have RP, mainly caused by gene variations inherited from either one or both of their parents. Mutated genes present incorrect instructions to photoreceptor cells, telling them to make an incorrect protein, or too little or too much protein. Cells need the appropriate amount of specific proteins to function right. A number of different gene mutations exist in retinitis pigmentosa. In Usher syndrome; for example, at least 14 disease-causing genes have been identified by researchers.
Genetic mutations may be passed from parent to child through 1 of 3 genetic inheritance patterns:
In autosomal recessive retinitis pigmentosa, both of a person's parents carry 1 copy of the mutated gene, yet do not experience symptoms themselves. Their children have a 25% chance of being affected by inheriting a mutated copy from each of their parents.
In autosomal dominant RP, usually 1 parent is affected and is the only parent with a gene variation. The parent's child has a 50% chance of being affected by inheriting the gene mutation from that parent.
In families with X-linked retinitis pigmentosa, a person's mother carries the mutated gene and her sons have a 50% chance of being affected by the disease. Daughters are carriers and are not usually affected. Some daughters; however, are affected - yet experience symptoms that are milder.
If one member of a person's family is diagnosed with retinitis pigmentosa it is strongly advised that other members of the person's family pursue an eye examination by a doctor who is specially trained to detect and treat retinal degenerative disorders. Discussing inheritance patterns and family planning with a genetic counselor may also be helpful.
Treating Retinitis Pigmentosa
At this point in time there is not much to be said concerning treatment of RP, although this may change at some point in the near future. Researchers are working towards treatments for retinitis pigmentosa. Work is being done to create implants for those with RP.
Genetic testing is available for retinitis pigmentosa. The testing assists with assessment of the risk of passing the disorder from parent to child. It also helps with receiving an accurate diagnosis, something that is very important. A person with an accurate diagnosis is in a better position to keep track of research developments, new findings, as well as new treatment approaches. It is important to make sure whether or not a person has RP and not a related syndrome, such as Usher's syndrome.
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