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A genetically heterogeneous condition associating
retinitis pigmentosa and deafness. The age of onset varies. Multiple
subtypes have been described.
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Retinitis Pigmentosa-Deafness Syndrome.
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Prevalence in the general population varies from
1:20,000 to 1:30,000 in Europeans.
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This medical entity was described by Charles Usher, a British
ophthalmologist, in 1914, who emphasized the hereditary nature. However, the earliest
description was given by Albrecht von Graefe in 1858, who commented on a relatively high
frequency in Jews in Berlin.
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Magnetic resonance imaging (MRI) has demonstrated characteristic morphological
abnormalities of the central nervous system. These abnormalities vary according to the syndrome
subtype. Twelve independent loci with six known genes have been reported.
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The combination of retinitis pigmentosa, sensorineural
deafness, abnormal vestibular function, mental retardation, psychosis, and
cerebellar ataxia lead to the diagnosis of Usher syndrome. Age of onset of
visual disturbance is variable depending on the subtype.
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It should be emphasized that this is a
heterogeneous condition and mental retardation is variable from normal to
severe. Vision may be lost in late or early childhood.
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Type I (USH I) is characterized by a congenital severe to profound preverbal deafness
present at birth, absent vestibular deterioration function, and early onset
of retinitis pigmentosa-like deterioration (typically by the age of 5 or
6 years and almost always by the age of 10 years). Different entities of USH
I have been described, but cannot be currently differentiated on a clinical
basis. It is also known as the French-Acadien (“Cajun”) of Louisiana
(chromosome 11p) and the French variety (chromosome 11q).
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Type II (USH II) has a milder postverbal hearing loss, apparently present from birth and
slowly evolutive (some suggests 1 decibel/per decade of life) and a later
onset of retinitis pigmentosa-like retinal degeneration (typically
between the ages of 10 and 20 years). Vestibular functions are normal and
stable.
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Type III (USH III) is a controversial form of Usher syndrome.
It is more frequent (40% of patients) in
eastern Finland, and is distinguished from USH II by its later onset with
rapid and progressive hearing loss and retinal degeneration. There is good
genetic evidence that the gene for USH III is located on a different
chromosome than the genes for USH I and USH II.
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In view of the variety of
presentations, each case has to be treated individually. In all cases,
hearing and visual function have to be evaluated.
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Patients may be profoundly deaf and
blind, and this combination makes communication potentially very difficult, especially during
induction of anesthesia and for the immediate postoperative care. There are no specific anesthetic
techniques to recommend.
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Consideration must be given to
medication, particularly the use of aminoglycosides in patients affected with Usher syndrome types II and III. Psychosis and bipolar
affective disorder are common in this group of ...