Microphthalmia with Coloboma, AD
Patient Information
Characteristics
Background and History
During embryological development, the eye sometimes does not develop to its full size, a condition known as microphthalmia. This can occur by itself but is occasionally accompanied by incomplete formation of the eyeball leading to a defect known as a coloboma (from the Greek word meaning unfinished). This malformation may involve various eye structures such as the iris (colored part of the eye), retina, and optic nerve.
Clinical Correlations
In the condition described here, the eyes are abnormally small and the colobomas can be seen as a ‘keyhole’ defect in the iris. The cornea (windshield of the eye) may be small along with other ocular structures and this creates an appearance suggesting the eyelids are not completely open. Vision defects are variable depending on what eye structures are involved. Rarely, the eye contains a cyst as well.
Genetics
Inheritance
This condition is rare and many reports involve only single kinships. The inheritance pattern in most families is autosomal dominant in which case the disorder is passed directly from parent to child in a vertical pattern since only a single mutation is necessary. A parent with this type of microphthalmia and coloboma can expect that half of his or her children will have the same condition.
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
In most cases of microphthalmos with coloboma, there are other abnormalities in the body. However, in the disorder described here, only the eye is abnormal. The diagnosis can be suspected from simple inspection when the normally round pupil has a ‘keyhole’ shape. This may be the only abnormality but sometimes there are other parts of the body that are involved and it is always important to have a complete eye and physical examination to detect other problems.
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