Retinitis pigmentosa

From WikiMD

Other Names: RP pigmentary retinopathy rod-cone dystrophy RP tapetoretinal degeneration

Retinitis pigmentosa is a group of related eye disorders that cause progressive vision loss. These disorders affect the retina, which is the layer of light-sensitive tissue at the back of the eye. In people with retinitis pigmentosa, vision loss occurs as the light-sensing cells of the retina gradually deteriorate.

The first sign of retinitis pigmentosa is usually a loss of night vision, which becomes apparent in childhood. Problems with night vision can make it difficult to navigate in low light. Later, the disease causes blind spots to develop in the side (peripheral) vision. Over time, these blind spots merge to produce tunnel vision. The disease progresses over years or decades to affect central vision, which is needed for detailed tasks such as reading, driving, and recognizing faces. In adulthood, many people with retinitis pigmentosa become legally blind.

Fundus of patient with retinitis pigmentosa, mid stage.jpg
Fundus of patient with retinitis pigmentosa, end stage.jpg

Cause

Mutations in more than 60 genes are known to cause nonsyndromic retinitis pigmentosa. More than 20 of these genes are associated with the autosomal dominant form of the disorder. Mutations in the RHO gene are the most common cause of autosomal dominant retinitis pigmentosa, accounting for 20 to 30 percent of all cases. At least 35 genes have been associated with the autosomal recessive form of the disorder. The most common of these is USH2A; mutations in this gene are responsible for 10 to 15 percent of all cases of autosomal recessive retinitis pigmentosa. Changes in at least six genes are thought to cause the X-linked form of the disorder. Together, mutations in the RPGR and RP2 genes account for most cases of X-linked retinitis pigmentosa.

The genes associated with retinitis pigmentosa play essential roles in the structure and function of specialized light receptor cells (photoreceptors) in the retina. The retina contains two types of photoreceptors, rods and cones. Rods are responsible for vision in low light, while cones provide vision in bright light, including color vision.

Mutations in any of the genes responsible for retinitis pigmentosa lead to a gradual loss of rods and cones in the retina. The progressive degeneration of these cells causes the characteristic pattern of vision loss that occurs in people with retinitis pigmentosa. Rods typically break down before cones, which is why night vision impairment is usually the first sign of the disorder. Daytime vision is disrupted later, as both rods and cones are lost.

Some of the genes associated with retinitis pigmentosa are also associated with other eye diseases, including a condition called cone-rod dystrophy. Cone-rod dystrophy has signs and symptoms similar to those of retinitis pigmentosa. However, cone-rod dystrophy is characterized by deterioration of the cones first, followed by the rods, so daylight and color vision are affected before night vision.

Inheritance

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. In 10 to 40 percent of all cases of retinitis pigmentosa, only one person in a family is affected. In these families, the disorder is described as simplex. It can be difficult to determine the inheritance pattern of simplex cases because affected individuals may have no affected relatives or may be unaware of other family members with the disease. Simplex cases can also result from a new gene mutation that is not present in other family members.

Symptoms

Retinitis Pigmentosa- tunnel vision.jpg

Symptoms often first appear in childhood. However, severe vision problems do not often develop before early adulthood.

  • Decreased vision at night or in low light. Early signs may include having a harder time moving around in the dark.
  • Loss of side (peripheral) vision, causing "tunnel vision."
  • Loss of central vision (in advanced cases). This will affect the ability to read.

For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed.

80%-99% of people have these symptoms

  • Abnormal electroretinogram
  • Abnormal retinal vascular morphology(Abnormality of retina blood vessels)
  • Abnormal testis morphology(Abnormality of the testis)
  • Abnormality of retinal pigmentation
  • Anteverted nares(Nasal tip, upturned)
  • Atypical scarring of skin(Atypical scarring)
  • Blindness
  • Conductive hearing impairment(Conductive deafness)
  • Hypogonadism(Decreased activity of gonads)
  • Hypoplasia of penis(Underdeveloped penis)
  • Intellectual disability(Mental deficiency)
  • Nystagmus(Involuntary, rapid, rhythmic eye movements)
  • Optic atrophy
  • Photophobia(Extreme sensitivity of the eyes to light)
  • Progressive night blindness
  • Sensorineural hearing impairment
  • Wide nasal bridge(Broad nasal bridge)

30%-79% of people have these symptoms

  • Cataract(Clouding of the lens of the eye)
  • Glaucoma
  • Hyperinsulinemia
  • Keratoconus(Bulging cornea)
  • Obesity(Having too much body fat)
  • Ophthalmoplegia(Eye muscle paralysis)

5%-29% of people have these symptoms

  • Hyperreflexia(Increased reflexes)
  • Type II diabetes mellitus(Noninsulin-dependent diabetes)

Diagnosis

Tests to evaluate the retina:

Treatment

There is no effective treatment for this condition. Wearing sunglasses to protect the retina from ultraviolet light may help preserve vision.

Some studies suggest that treatment with antioxidants (such as high doses of vitamin A palmitate) may slow the disease. However, taking high doses of vitamin A can cause serious liver problems. The benefit of treatment has to be weighed against risks to the liver.

Clinical trials are in progress to assess new treatments for retinitis pigmentosa, including the use of DHA, which is an omega-3 fatty acid.

Other treatments, such as microchip implants into the retina that act like a microscopic video camera, are in the early stages of development. These treatments may be useful for treating blindness associated with RP and other serious eye conditions.

A vision specialist can help you adapt to vision loss. Make regular visits to an eye care specialist, who can detect cataracts or retinal swelling. Both of these problems can be treated.

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. The medication(s) listed below have been approved by the Food and Drug Administration (FDA) as orphan products for treatment of this condition.

  • Voretigene neparvovec-rzyl (Brand name: Luxturna)An adeno-associated virus vector-based gene therapy indicated for the treatment of patients with confirmed biallelic RPE65 mutation-associated retinal dystrophy. Patients must have viable retinal cells determined by a treating physician.

Prognosis

The disorder will continue to progress slowly. Complete blindness is uncommon.

Epidemiology

Retinitis pigmentosa is one of the most common inherited diseases of the retina (retinopathies). It is estimated to affect 1 in 3,500 to 1 in 4,000 people in the United States and Europe.

NIH genetic and rare disease info

Retinitis pigmentosa is a rare disease.

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WikiMD Resources - Retinitis pigmentosa


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