Corneal Dystrophy, Congenital Endothelial 2
Patient Information
Characteristics
Background and History
This congenital disorder of the cornea (windshield) of the eye was first described in 1960. It is only one of many causes of cloudy corneas but this one usually has its onset in early childhood.
Clinical Correlations
The cornea may be cloudy at birth and at that time may be confused with congenital glaucoma or another form of congenital corneal clouding (Harboyan syndrome). The latter, however, is associated with hearing loss which may not be evident at birth. The swelling of the cornea, which results in the clouding, may be progressive. Vision is, of course, impacted but near normal vision occurs in many individuals. The disorder is caused by a genetic defect that leads to damage in the posterior layer of the cornea, called the endothelium. This single layer of cells is importance in the maintenance of normal hydration of the cornea and, when damaged, allows the cornea to swell with fluid.
Genetics
Inheritance
This is an autosomal recessive disorder resulting from a gene mutation on chromosome 20. It occurs in sibships usually without a family history because the clinically normal parents are carriers with only a single mutation. The parents are often related. The disease results when each of the parents passes on their mutant gene, leading to a double dose of the mutation.
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 can diagnose this disorder although simple inspection of the eye can discern the clouding of the cornea. Other conditions must be ruled out and a gene test must be used to confirm the diagnosis. The visual prognosis is good. In severe cases a corneal graft may be necessary to restore good vision. The surgical success rate is high.
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