OMIM ID:
Retinal Dystrophy with Inner Retinal Abnormalities
Alternate Names
Defective Genes
Clinical Characteristics
Ocular Features
Otherwise healthy individuals note onset of light sensitivity between 25 and 40 years of age. Central vision is progressively lost with average vision levels of 20/50. In some patients vision is 20/400 but peripheral vision remains normal on visual field testing. Small central and centrocecal scotomas can be demonstrated. There is general hyper-reflectivity of the ganglion cell and nerve fiber layers with the latter decreased in thickness especially in the foveal area of all patients. The optic nerve is often pale. The ERG recordings are consistent with inner retinal dysfunction with an absent b-wave and a normal a-wave response. Older patients have additional photopic response abnormalities and delayed implicit times. Color vision in younger individuals was reported to be normal but older persons had mild deuteranopia.
Systemic Features
No systemic disease was noted in the single reported family. Specifically, no dementia was present in affected individuals (vida infra).
Genetics
Inheritance
This condition has been identified in a single large 3-generation family. A missense heterozygous mutation in the ITM2B gene (13q14.2) is responsible. The gene product localizes to the inner nuclear and ganglion cell layers in the eye and co-localizes with the amyloid beta precursor protein of Alzheimer disease in cerebral tissue.
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