Retinitis Pigmentosa - Macular Degeneration

What are the early onset or juvenile forms of inherited Macular Degeneration?

Increasingly sophisticated diagnostic and examination methods have helped scientists distinguish among some of the forms of Macular Degeneration and classify them according to the inheritance pattern of the disease. There are three possible inheritance patterns: Autosomal Dominant, in which an affected parent can have both affected or unaffected children; Autosomal Recessive, in which unaffected parents can have affected children if both parents are carriers of the gene; and X-Linked, in which women carry the affected gene but do not typically experience vision problems - their sons will be affected and their daughters, most often, will not have the disease but will carry the affected gene.

Inherited Autosomal Dominant conditions include:

Best Disease, or Vitelliform Dystrophy, which causes progressive changes in the retina with great variability among patients. Symptoms usually appear in affected individuals between the ages of 4 and 10, but may not be diagnosed until much later. Most patients have reasonably good vision for man ears, but eventually their vision decreases to 20/100 or less, particularly if the macula is scarred or subretinal bleeding occurs.

The gene for this disease has been mapped to the long arm of Chromosome 11, but the exact location is not yet known.

Dominant Drusen, which are caused by the accumulation of drusen, yellow-white deposits, in the macular area. Drusen deposits usually appear in the first three decades of life, and become larger as a person ages. Decreased vision may not be noticed until the fourth decade, with vision varying between 20/30 and 20/80. If the drusen causes other complications in the retina, vision may decrease to 20/200.

Sorsby Macular Dystrophy, which is a rare disorder in which new blood vessels grow under the fovea, resulting in fluid build-up in the macular, haermorrage, and general wasting of other layers of tissue in the eye. Usually symptoms do not appear until after the age of 40. Drusen may also be present. People with this disorder may experience a rapid decrease in vision. The gene for this disorder has been identified as the TIMP3 gene, which is located on the long arm of Chromosome 22.

Pigment Pattern Dystrophy, which describes a group of disorders that includes Butterfly-shaped Pigment Dystrophy of the fovea, North Carolina Macular Dystrophy, Macroreticular (Spider) Dystrophy and Sjögren Reticular Pigment Epithelium Dystrophy. The macular changes in these patients can occur at any age, but usually first appear in childhood. Many patients do not experience symptoms and may have visual acuities in the 20/20 to 20/80 range. Some of the genes have been identified for these disorders and are located on Chromosome 6.

Diseases inherited through the Autosomal Recessive pattern include:

Stargardt Dystrophy which is the most common form of Inherited Macular Degeneration in patients under the age of 20. It is usually first noticeable between the ages of 8 and 12. Patients with previously normal vision develop irregularly shaped yellowish-white flecks or spots in the macula. This causes decreased central vision, which eventually deteriorates to 20/200 as the flecks in the macula grow. In late stages of the disease, there may also be some impairment of colour vision. The major gene for this disease has been located to the short arm of Chromosome 1. The gene has recently been identified as the ABCR gene. The protein produced by this gene is involved in the energy transport to and from the photo receptor cells. Retina South Africa has a gene tracking project to identify the genes causing Stargardt Dystrophy in South African Families. This is a pre-requisite to any future gene based therapy.

Fundus Flavimaculatus, is a condition similar to Stargardt Disease but varies in its age of onset and severity. When there is macular damage, vision can deteriorate to 20/200, although it usually remains between 20/50 and 20/80. Damage to the macula first appears in the adolescent and early adult years, and the area of damage may gradually spread.

Peripapillary (pericentral) Choroidal Dystrophy is a condition which causes wasting of the blood vessels that surround the optic nerve. Patients first notice symptoms in the late adult years, when the macula is affected.

Stationary cone disorders are present at birth and have symptoms decreased acuity, decreased colour vision, sensitivity to light - that do not worsen with age. There are several types of stationary cone disorders (for example, cone monochromatism, blue cone monochromatism, dichromatism, trichromatism) with differing prognoses for visual acuity.

There are very few families whose Macular Degeneration has been mapped to the X Chromosome. At this time, no specific disease names or genes have been identified.