Retinal Dystrophy with or without Macular Staphyloma
Patient Information
Characteristics
Background and History
This is a recently reported and rare form of progressive hereditary retinal degeneration. It has many characteristics of the more common retinal dystrophy (degeneration) widely known as retinitis pigmentosa. However, some patients have a posterior, localized bulging of the eyeball known as a staphyloma.
Clinical Correlations
Only a few patients have been reported and not all have had complete eye examinations. However, night vision difficulties and a general reduction in vision have been reported by individuals in the first decade of life. This is a progressive condition and legal blindness is common by midlife. Visual field testing shows a typical constriction of side vision while electrophysiological testing of retinal function (using an ERG or electroretinogram) shows severe dysfunction of the rods and cones. It is not known what proportion of patients have staphylomas.
There are no characteristic abnormalities in the rest of the body and there is no known impact on longevity.
Genetics
Inheritance
This is an autosomal recessive condition in which mutations in both members of a specific pair of genes are responsible. The parents, each of whom carries one mutation, are clinically normal, but in such pairings they confer a 25% risk for this condition to each of their children.
Pedigree
Autosomal recessive
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
Diagnosis and Prognosis
Only an ophthalmologist is able to diagnose this disorder by a complete eye examination. It is not known if any of the eye signs are present at birth but abnormalities have been reported by the age of 5 years and appropriate tests should be done. No treatment has been reported but low vision aids could be helpful, especially for educational purposes early in life.
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