Microphthalmia with Retinitis Pigmentosa
Patient Information
Characteristics
Background and History
Several gene mutations result in eyeballs (globes) that are either larger or smaller than normal. In nanophthalmos and microphthalmia, the globe is smaller than average and for some, but not all patients, there can be problems in the retina as well. Many patients with such small eyeballs have a significant risk of acute glaucoma.
Clinical Correlations
In this disorder, the small globe results in extreme farsightedness. The retinal problems associated with this syndrome are responsible for loss of vision with nightblindness beginning in the third decade of life. The loss of vision can be severe. The outside coating of the eye (sclera) is thickened, the retina may be split and abnormal clumping of pigment is seen throughout the retina. Small deposits called drusen are present in the optic nerve. Glaucoma is not a feature.
No systemic disease is present and lifespan is normal.
Genetics
Inheritance
Based on the single family reported and the pattern of mutations seen in the DNA, this seems to be an autosomal recessive disorder. The parents have a single dose of the mutation while the affected children have a double dose as expected for this pattern of inheritance. The parents can expect that on average one in four of their children will be affected.
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 clinical features of this disorder are seen only in the eyes and therefore an ophthalmological examination is necessary to make the diagnosis. An electroretinogram (ERG) documents the retinal damage. No treatment is available but low vision aids could be helpful at least in early stages of the disease.
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