Retinal Dystrophy, Newfoundland Type
Patient Information
Characteristics
Background and History
A large number of gene mutations lead to diseases of the retina. Some such as retinitis pigmentosa are relatively common while others such as the one described here are more rare and limited in distribution. Six family pedigrees of the Newfoundland type have been reported from that country.
Clinical Correlations
Young children in the first decade of life report difficulty seeing at night (night blindness). Physical examination of the eye may not reveal changes until later but a special test called an electroretinogram documents some damage to the light-responsive cells in the retina. Vision loss is progressive and by the 2nd and 3rd decades loss of vision becomes pronounced and legal blindness is common among young adults. By then there are obvious pigmentary changes and narrowing of the blood vessels of the retina may be seen. There are no known abnormalities outside of the eye.
Genetics
Inheritance
This is an autosomal recessive condition requiring that both copies of a specific gene are changed. Parents who carry one copy have normal retinas but each of their children has a 25% chance of developing the condition.
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
The diagnosis can only be made by an ophthalmologist after an examination of the eye. No treatment is available and many individuals become legally blind before middle age. Tinted lenses though may be helpful.
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