What gene change causes retinitis pigmentosa?
Retinitis pigmentosa is a term which describes a group of conditions, each with its own distinct genetic cause. There are more than 60 genes alone that cause non-syndromic retinitis pigmentosa, with an additional dozens of genes causing the syndromic and systemic forms of retinitis pigmentosa. Each of these genes provides instructions for making proteins that allow the retina, the area of the eye that responds to light, to function properly. Changes in any of these genes can cause the proteins to be made improperly or not at all, leading to damage to the retina. A list of genes associated with non-syndromic retinitis pigmentosa can be found in the Gene Review for this condition.
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How does a gene change cause retinitis pigmentosa?
There are over 60 genes which have been associated with non-syndromic retinitis pigmentosa. Each of those genes provides instructions for making proteins that allow the retina, the area of the eye that responds to light, to function properly. Specifically, these genes help build the photoreceptors ("rods and cones") and the layer of cells known as the "retinal pigment epithelium." Rods are the cells in the retina which respond to light and dark changes and are responsible for vision when there is not much light present. Cones are the cells in the retina which respond to color and are responsible for vision where there is a lot of light present. The retinal pigment epithelium is responsible for light absorption, nourishment of the retina, and immune function of the eye.
Changes in any of the genes associated with retinitis pigmentosa can cause proteins essential to the photoreceptors and/or the retinal pigment epithelium to be made improperly or not at all. This can lead to death of the photoreceptor cells, causing progressive loss of both rods and cones. The rods typically are affected first, causing night blindness to be the first symptom of retinitis pigmentosa, with the cones being lost subsequently and thus day vision being disrupted later.
There are an entirely different set of genes associated with syndromic and systemic forms of retinitis pigmentosa. Those genes cause not only retinitis pigmentosa, but other neurologic problems such as hearing loss and/or problems in other organ systems such as heart disease. These conditions are typically not called by the name "retinitis pigmentosa" and instead retinitis pigmentosa is considered one symptom among others associated with that particular diagnosis. For information about how the genes associated with a specific syndromic or systemic form of retinitis pigmentosa cause that disease, search the specific diagnosis name (such as "Bardet-Biedl syndrome" or "Usher syndrome") in the search box at Genetics Home Reference.
Does anything make retinitis pigmentosa worse?
Retinitis pigmentosa is inherently a degenerative disease. This means that it gets worse naturally over time. The age at which symptoms onset and the speed of disease progression depends on the specific type of retinitis pigmentosa that a person has. Nonetheless, it is recommended that individuals with retinitis pigmentosa avoid high-dose vitamin E supplements (≥400 IU per day). A study in 1993 showed that individuals taking these higher daily doses of vitamin E have faster disease progression than those who had no supplemental vitamin E or who took small supplementary amounts. To read more about this study you can access the summary of the journal publication here.