A genetically heterogeneous condition associating retinitis pigmentosa and deafness. The age of onset varies. Multiple subtypes have been described. Leading cause of deaf-blindness.
Retinitis Pigmentosa-Deafness Syndrome.
Prevalence in the general population varies from 1:20,000 to 1:30,000 in Europeans.
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.
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.
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.
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.
Type I (USH I): Accounts around 40% of patients affected with this medical condition. 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). Seven causal mutation subtypes (A-G) of USH I have been described, but cannot be currently differentiated on a clinical basis. It is also known as the French-Acadian (“Cajun”) of Louisiana (chromosome 11p) and the French variety (chromosome 11q).
Type II (USH II): Affects approximately 60% of patients with this disease. Characterized by 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. Three subtypes described (A-C).
Type III (USH III): Represents less than 3% of affected individuals. It is a controversial form of Usher Syndrome. It is more frequent in eastern Finland and Ashkenazi Jewish population. It is distinguished from USH II by its later onset with rapid and progressive hearing loss and retinal degeneration.
Precautions before anesthesia
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.