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Retinitis pigmentosa is the leading cause of inherited blindness, with approximately 1/4,000 individuals experiencing the non-syndromic form of their disease within their lifetime. It is estimated that 1.5 million people worldwide are currently affected. Early onset RP occurs within the first few years of life and is typically associated with syndromic disease forms, while late onset RP emerges from early to mid-adulthood.
Autosomal dominant and recessive forms of retinitis pigmentosa affect both male and female populations equally; however, the less frequent X-linked form of the disease affects male recipients of the X-linked mutation, while females usually remain unaffected carriers of the RP trait. The X-linked forms of the disease are considered severe, and typically lead to complete blindness during later stages. In rare occasions, a dominant form of the X-linked gene mutation will affect both males and females equally.
Due to the genetic inheritance patterns of RP, many isolate populations exhibit higher disease frequencies or increased prevalence of a specific RP mutation. Pre-existing or emerging mutations that contribute to rod photoreceptor degeneration in retinitis pigmentosa are passed down through familial lines; thus, allowing certain RP cases to be concentrated to specific geographical regions with an ancestral history of the disease. Several hereditary studies have been performed to determine the varying prevalence rates in Maine (USA), Birmingham (England), Switzerland (affects 1/7000), Denmark (affects 1/2500), and Norway. Navajo Indians display an elevated rate of RP inheritance as well, which is estimated as affecting 1 in 1878 individuals. Despite the increased frequency of RP within specific familial lines, the disease is considered non-discriminatory and tends to equally affect all world populations.
"Best disease" is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In most cases, an affected person has one parent with the condition.
The inheritance pattern of adult-onset vitelliform macular dystrophy is definitively autosomal dominant. Many affected people, however, have no history of the disorder in their family and only a small number of affected families have been reported. This is because the penetrance of the condition is incomplete; therefore, it is possible for an individual to have a copy of the mutant allele and not display the VMD phenotype. The ratio of males to females is approximately 1:1.
RP may be:
(1) Non-syndromic, that is, it occurs alone, without any other clinical findings,
(2) Syndromic, with other neurosensory disorders, developmental abnormalities, or complex clinical findings, or
(3) Secondary to other systemic diseases.
- RP combined with deafness (congenital or progressive) is called Usher syndrome.
- Alport's syndrome is associated with RP and an abnormal glomerular-basement membrane leading nephrotic syndrome and inherited as X-linked dominant.
- RP combined with ophthalmoplegia, dysphagia, ataxia, and cardiac conduction defects is seen in the mitochondrial DNA disorder Kearns-Sayre syndrome (also known as Ragged Red Fiber Myopathy)
- RP combined with retardation, peripheral neuropathy, acanthotic (spiked) RBCs, ataxia, steatorrhea, is absence of VLDL is seen in abetalipoproteinemia.
- RP is seen clinically in association with several other rare genetic disorders (including muscular dystrophy and chronic granulomatous disease) as part of McLeod syndrome. This is an X-linked recessive phenotype characterized by a complete absence of XK cell surface proteins, and therefore markedly reduced expression of all Kell red blood cell antigens. For transfusion purposes these patients are considered completely incompatible with all normal and K0/K0 donors.
- RP associated with hypogonadism, and developmental delay with an autosomal recessive inheritance pattern is seen with Bardet-Biedl syndrome
Other conditions include neurosyphilis, toxoplasmosis and Refsum's disease.
Vitelliform macular dystrophy or vitelliform dystrophy is an irregular autosomal dominant eye disorder which can cause progressive vision loss. This disorder affects the retina, specifically cells in a small area near the center of the retina called the macula. The macula is responsible for sharp central vision, which is needed for detailed tasks such as reading, driving, and recognizing faces. The condition is characterized by yellow (or orange), slightly elevated, round structures similar to the yolk (Latin "vitellus") of an egg.
This condition is linked to the X chromosome.
- Siberian Husky - Night blindness by two to four years old.
- Samoyed - More severe disease than the Husky.
Few studies have examined the prevalence of FCED on a large scale. First assessed in a clinical setting, Fuchs himself estimated the occurrence of dystrophia epithelialis corneae to be one in every 2000 patients; a rate that is likely reflective of those who progress to advanced disease. Cross-sectional studies suggest a relatively higher prevalence of disease in European countries relative to other areas of the world. Fuchs' dystrophy rarely affects individuals under 50 years of age.
At least one type of autosomal dominant cone-rod dystrophy is caused by mutations in the guanylate cyclase 2D gene (GUCY2D) on chromosome 17.
A cone dystrophy is an inherited ocular disorder characterized by the loss of cone cells, the photoreceptors responsible for both central and color vision.
Reis-Bücklers corneal dystrophy is not associated with any systemic conditions.
Different corneal dystrophies are caused by mutations in the CHST6, KRT3, KRT12, PIP5K3, SLC4A11, TACSTD2, TGFBI, and UBIAD1 genes. Mutations in TGFBI which encodes "transforming growth factor beta induced" cause several forms of corneal dystrophies including granular corneal dystrophy, lattice corneal dystrophy, epithelial basement membrane dystrophy, Reis-Bucklers corneal dystrophy, and Thiel–Behnke dystrophy.
Corneal dystrophies may have a simple autosomal dominant, autosomal recessive or rarely X-linked recessive Mendelian mode of inheritance:
Several mutations have been implicated as a cause of Oguchi disease. These include mutations in the arrestin gene or the rhodopsin kinase gene.
The condition is more frequent in individuals of Japanese ethnicity.
This type of PRA has an early onset of severe vision loss. It is caused by a defect in the gene for cGMP-phosphodiesterase, which leads to retinal levels of cyclic guanosine monophosphate ten times normal.
Recurrence within a few years occurs in all patients following corneal transplantation. Soft contact lenses are effective in decreasing recurrences.
Granular corneal dystrophy is a slowly progressive corneal dystrophy that most often begins in early childhood.
Granular corneal dystrophy has two types:
- Granular corneal dystrophy type I , also corneal dystrophy Groenouw type I, is a rare form of human corneal dystrophy. It was first described by German ophthalmologist Arthur Groenouw in 1890.
- Granular corneal dystrophy type II, also called Avellino corneal dystrophy or combined granular-lattice corneal dystrophy is also a rare form of corneal dystrophy. The disorder was first described by Folberg et al. in 1988. The name Avellino corneal dystrophy comes from the first four patients in the original study each tracing their family origin to the Italian province of Avellino.
Choroideremia (; CHM) is a rare, X-linked recessive form of hereditary retinal degeneration that affects roughly 1 in 50,000 males. The disease causes a gradual loss of vision, starting with childhood night blindness, followed by peripheral vision loss, and progressing to loss of central vision later in life. Progression continues throughout the individual's life, but both the rate of change and the degree of visual loss are variable among those affected, even within the same family.
Choroideremia is caused by a loss-of-function mutation in the "CHM" gene which encodes Rab escort protein 1 (REP1), a protein involved in lipid modification of Rab proteins. While the complete mechanism of disease is not fully understood, the lack of a functional protein in the retina results in cell death and the gradual deterioration of the choroid, retinal pigment epithelium (RPE), and retinal photoreceptor cells.
As of 2017, there is no treatment for choroideremia; however, retinal gene therapy clinical trials have demonstrated a possible treatment.
Corneal transplant is not needed except in very severe and late cases.
Light sensitivity may be overcome by wearing tinted glassess.
DM1 is the most common form of myotonic muscular dystrophy diagnosed in children, with a prevalence ranging from 1 per 100,000 in Japan to 3-15 per 100,000 in Europe. The prevalence may be as high as 1 in 500 in regions such as Quebec, possibly due to the founder effect. In most populations, DM1 appears to be more common than DM2. However, recent studies suggest that type 2 may be as common as type 1 among people in Germany and Finland.
The incidence of congenital myotonic dystrophy is thought to be about 1:20,000. DM occurs in about 1 per 7,000–8,000 people and has been described in people from all over the world. It affects males and females approximately equally. About 30,000 people in the United States are affected.
While nothing currently can be done to stop or reverse the retinal degeneration, there are steps that can be taken to slow the rate of vision loss. UV-blocking sunglasses for outdoors, appropriate dietary intake of fresh fruit and leafy green vegetables, antioxidant vitamin supplements, and regular intake of dietary omega-3 very-long-chain fatty acids are all recommended.
One study found that a dietary supplement of lutein increases macular pigment levels in patients with choroideremia. Over a long period of time, these elevated levels of pigmentation could slow retinal degeneration. Additional interventions that may be needed include surgical correction of retinal detachment and cataracts, low vision services, and counseling to help cope with depression, loss of independence, and anxiety over job loss.
The disease has been associated with mutations in TGFBI gene on chromosome 5q which encodes for keratoepithelin. The inheritance is autosomal dominant.
Oguchi disease, also called congenital stationary night blindness, Oguchi type 1 or Oguchi disease 1, is an autosomal recessive form of congenital stationary night blindness associated with fundus discoloration and abnormally slow dark adaptation.
Corneal dystrophy is a group of rare hereditary disorders characterised by bilateral abnormal deposition of substances in the transparent front part of the eye called the cornea.
Phototherapeutic keratectomy (PTK) done by an ophthalmologist can restore and preserve useful visual function for a significant period of time in patients with anterior corneal dystrophies including EBMD.
Lattice corneal dystrophy has two types:
- type I: with no systemic association. It is caused by mutations in TGFBI gene encoding keratoepithelin, which maps to chromosome 5q.
- type II or Finnish type amyloidosis: associated with manifestations of systemic amyloidosis due to accumulation of gelsolin. Associated conditions may include cutis laxa and ataxia.
- type III is also described which has an onset at age 70 to 90 years and is not associated with systemic amyloidosis.
The disease is found across 5 continents (30 countries) and is frequently seen in French Canadians, with a prevalence 1:1000. OPMD affects males and females equally, and affected individuals have been found in Europe (France), Jewish Ashkenazi, and Spanish Americans.
A number of mutations causing this disease have been described in the M1S1 (TACSTD2) gene encoding "Tumor-associated calcium signal transducer 2", but not all patients have these mutations, suggesting involvement of other genes.