Macular Dystrophy with Central Cone Involvement
Patient Information
Characteristics
Background and History
The macula is a specialized area of the retina containing the highest concentration of so-called receptor cells that respond to light. It is therefore the area we use for our most acute vision such as reading. The central macula primarily contains cones, the receptors that enable us to see color. There are many inherited conditions that impact these retinal receptors as the result of gene changes (mutations) and some of them, like the disorder described here, primarily cause vision problems due to the macular involvement.
Clinical Correlations
In this disorder loss of vision is usually noted about midlife, in the third to sixth decades of life. The earliest retinal changes, when this occurs, can be seen in the macula. Testing reveals loss of receptor cell function primarily in the macula, creating a blind spot (scotoma) early in the disease process but this eventually spreads outward to involve more of the retina. Sometimes, later in the disease, the optic nerve that carries light responses from the eye to the brain shows evidence of damage as well. Because the cones are primarily damaged there may be loss of normal color vision.
There are no abnormalities in other organs.
Genetics
Inheritance
This condition result when both copies of a gene are changed or mutated. Carriers such as parents that carry only one changed copy do not have this macular disease. However, children born to two such parents each have a 25% chance of inheriting this 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 is made by an ophthalmologist or medical eye doctor. Special tests such as visual fields and electroretinograms (ERG) help make the diagnosis since a simple eye examination by visual inspection of the macula and retina is usually unable to distinguish this condition from others.
Progressive damage to more receptor cells inevitably leads to increasing vision loss. There is no treatment available.
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