Corneal Dystrophy, Posterior Polymorphous 2
Patient Information
Characteristics
Background and History
Numerous gene mutations lead to degeneration (dystrophy) of the cornea. These dystrophies are generally classified according to the clinical appearance which may include clouding of the cornea or the appearance of various types of deposits. The cornea is the normally clear windshield of the eye and when it becomes cloudy, vision becomes blurred.
Clinical Correlations
Posterior polymorphous corneal dystrophy has been divided into three types, each of which are caused by mutations in different genes. All of these may be apparent in early childhood, or they may not be diagnosed until early adult life. They commonly appear as small bumps on the back surface of the cornea and when these become large enough or coalesce sufficiently, the cornea retains too much fluid and becomes cloudy. If this is extensive enough, the vision becomes blurry.
No systemic disease is consistently associated with posterior polymorphous dystrophy of the cornea.
Genetics
Inheritance
All three types of posterior polymorphous corneal dystrophy are inherited as autosomal dominant diseases. This means that family patterns show the disease to be passed from parent to child in a vertical pattern.
Pedigree
Autosomal dominant
Autosomal dominant disorders require only one mutation for the disease to be expressed. Since an affected parent has two chromosomes, only one of which has the mutant gene, parents can expect that half (50%) of their children will receive that one and inherit the disease. It is common for individuals that inherit the mutation, however, to not have evidence of the disease (nonpenetrance).
Autosomal dominant inheritance leads to a vertical pattern of transmission
Diagnosis and Prognosis
The prognosis for vision and health is generally good. However, the severity of disease is highly variable and predictions cannot be made in individual cases. It is not uncommon for vision to be sufficiently reduced by the third decade that a corneal transplant is required. However, transplants have been done in older individuals, and many times no treatment is required.
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