Night Blindness, Congenital Stationary, CSNB1E
Patient Information
Characteristics
Background and History
Various conditions causing poor night vision, sometimes called night blindness, have been known for centuries. Many disorders of the retina cause night blindness and most of these are progressive and associated with other ocular disease. However, several conditions causing difficulties with night vision are not progressive nor are they part of other syndromes. These are generally referred to as congenital stationary night blindness (CSNB).
Clinical Correlations
Difficulty seeing at night is the primary symptom of congenital stationary night blindness. The condition is present at birth and does not progress. Daytime vision may be reduced to some degree as well. Mild color vision defects can sometimes be detected.
Genetics
Inheritance
At least 9 different mutated genes are known to cause CSNB. This type is inherited in an autosomal recessive pattern which requires that both parents contribute the specific mutation. The parents, who are clinically normal, are carriers and can expect that each of their children have a 1 in 4 (25%) chance of inheriting CSNB.
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
Diagnosis is based on an ophthalmological examination. An electroretinogram (ERG) test is important to establish the diagnosis and to rule out other retinal disease. This is a stationary disease without significant progression and no systemic disease is present. The clinical findings are so similar to other types of congenital stationary nightblindness that DNA studies are required to confirm the diagnosis.
The only treatment is correction of refractive errors if needed.
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