Disease characteristics/Usher syndrome type II is characterized by congenital (i.e., prelingual) bilateral sensorineural hearing loss that is mild to moderate in the low frequencies and severe to profound in the higher frequencies, intact vestibular responses, and retinitis pigmentosa (RP). RP is progressive, bilateral, symmetric retinal degeneration that begins with night blindness and constricted visual fields (tunnel vision) and eventually includes decreased central visual acuity; the rate and degree of vision loss vary within and among families. Diagnosis/testing/The diagnosis of Usher syndrome type II is established on clinical grounds using electrophysiologic and subjective tests of hearing and retinal function. Biallelic mutations in one of three genes are known to cause Usher syndrome type II: USH2A (accounting for up to 80% of cases), GPR98 (VLGR1), and DFNB31. A fourth locus has been provisionally mapped to 15q. Management/ Treatment of manifestations: Early fitting of hearing aids and speech training to normalize language. Surveillance: Routine auditory evaluation to detect changes that may require modifications to hearing aids; routine ophthalmologic evaluation to detect potentially treatable complications such as cataracts. Agents/circumstances to avoid: Tunnel vision and night blindness can increase the likelihood of accidental injury. Competition in sports requiring a full range of vision may be difficult and possibly dangerous. Progressive loss of peripheral vision impairs the ability to safely drive a car. Evaluation of relatives at risk: The hearing of at-risk sibs should be assessed as soon after birth as possible to allow early diagnosis and treatment of hearing loss. Genetic counseling/Usher syndrome type II is inherited in an autosomal recessive manner. Each subsequent pregnancy of a couple who has had a child with Usher syndrome type II has a 25% chance of resulting in an affected child, a 50% chance of resulting in an unaffected child who is a carrier, and a 25% chance of resulting in an unaffected child who is not a carrier. Prenatal testing is possible for pregnancies at increased risk if the disease-causing mutations have been identified in the family.
Posted on: Thu, 26 Sep 2013 03:39:23 +0000
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