Familial Internal Retinal Membrane Dystrophy
Alternate Names
Defective Genes
Clinical Characteristics
Ocular Features
Folds in the internal limiting membrane are commonly seen, especially in the macula. Intraretinal edema is seen throughout but may be most evident in the macula which often appears cystic. Superficial microcystic changes in the retina are concentrated in the posterior pole. The internal limiting membrane often appears thickened and filamentous material may be present in areas where it is separated from the retina. The inner retina may have schisis cavities. Visual acuity remains good until midlife.
This disorder is considered by some to result from a primary defect in Muller cells resulting in permeability defects on the retinal surface. Evidence for this hypothesis comes from ERG studies in which light adapted responses showed a delayed and reduced b-wave, with broad and delayed ON and OFF responses and a missing flicker response. However, responses may be inconsistent between the two eyes and more studies are needed.
Histologic studies show endothelial cell swelling, pericyte degeneration, and basement membrane thickening in retinal capillaries.
Systemic Features
No systemic abnormalities have been reported.
Genetics
Inheritance
Several families with transmission patterns characteristic of autosomal dominant inheritance have been reported. However, no locus or mutation has been reported.
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