ITM2B

Retinal Dystrophy with Inner Retinal Abnormalities

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

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
Treatment
Treatment Options: 

No treatment for the retinal disease is available but photosensitive individuals may benefit from tinted lenses.  Low vision aid can be useful for near vision.

References
Article Title: 

The familial dementia gene revisited: a missense mutation revealed by whole-exome sequencing identifies ITM2B as a candidate gene underlying a novel autosomal dominant retinal dystrophy in a large family

Audo I, Bujakowska K, Orhan E, El Shamieh S, Sennlaub F, Guillonneau X, Antonio A, Michiels C, Lancelot ME, Letexier M, Saraiva JP, Nguyen H, Luu TD, Leveillard T, Poch O, Dollfus H, Paques M, Goureau O, Mohand-Said S, Bhattacharya SS, Sahel JA, Zeitz C. The familial dementia gene revisited: a missense mutation revealed by whole-exome sequencing identifies ITM2B as a candidate gene underlying a novel autosomal dominant retinal dystrophy in a large family. Hum Mol Genet. 2014 Jan 15;23(2):491-501..

PubMed ID: 
24026677

Cerebral Amyloid Angiopathy

Clinical Characteristics
Ocular Features: 

Posterior polar cataracts appear during the third decade of life.

Systemic Features: 

Progressive hearing loss has its onset in the third decade and becomes severe in the 5th decade.  Progressive dementia, often in the form of paranoid psychosis, begins about age 50.  Cerebellar ataxia and intention tremor have their onset in midlife.  There is a diffuse atrophy throughout the brain and cranial nerves are demyelinated.  Blood vessels throughout the CNS, spinal cord and retina show an amyloid angiopathy.  Intracranial hemorrhage is a significant risk and, when lobar in location, carries a significant risk of mortality within months.  Death generally occurs in the 5th and 6th decades of life.

Genetics

Pedigree patterns in the few reported families are consistent with autosomal dominant inheritance.  A mutation has been found in the ITM2B gene located at 13q14.

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

No treatment is available.

References
Article Title: 

Heredopathia ophthalmo-oto-encephalica

Stromgrem, E. Heredopathia ophthalmo-oto-encephalica. In: Myrianthopoulos, N.C. Handbook of Clinical Neurology. Neurogenetic directory. New York: Elsevier/North Holland (pub.) 42, Part I: 150-152, 1981.

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