Corneal Dystrophy, Macular
Patient Information
Characteristics
Background and History
The cornea is the normally clear windshield at the front of the eye. A number of gene mutations result in the deposition of abnormal material in this tissue which causes cloudiness and interferes with vision.
Clinical Correlations
Macular corneal dystrophy may have its onset in infancy but sometimes is not diagnosed until the second or third decade of life. Cells in the deeper layers of the cornea accumulate abnormal material creating a general cloudiness which is progressive. The impairment of vision can be severe by mid-life and may require a corneal transplant. This is not a systemic disease although abnormal levels of a sulfur containing compound have been detected in the blood.
Genetics
Inheritance
This is an autosomal recessive disorder which requires the inheritance of two copies, one from each parent, of the mutation. The family pattern of affected individuals is, therefore, horizontal since the disorder is not passed from an affected parent to a child.
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
It is often possible to make a tentative diagnosis by seeing cloudiness in the corneas (this is a bilateral disease) but the exact diagnosis requires an ophthalmological examination since several corneal dystrophies appear superficially similar.
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