Usher Syndrome Type II
Patient Information
Characteristics
Background and History
Usher syndrome is comprised of a group of diseases with a distinctive combination of hearing and progressive vision loss. It is named for a Scottish ophthalmologist, Charles Howard Usher, who recognized their hereditary nature although he was not the first to describe the condition.
Clinical Correlations
The clinical features of type II Usher syndrome are somewhat similar to those of type I but balance problems and occasional mental deficits are lacking. Hearing is impaired somewhat from birth and there is some worsening with age but the profound congenital deafness found in type I does not occur. Hence, many individuals develop speech. Balance and coordination are usually normal.
Loss of night vision becomes symptomatic by adolescence and is progressive. By young adulthood, tunnel vision may be severe with only a small area of seeing left. Rare patients may become blind and cataracts may be present.
Genetics
Inheritance
All types of Usher syndrome follow an autosomal recessive pattern of inheritance. Parents who carry a single mutation do not have symptoms but if both mother and father carry the mutation, each of their offspring has a 25% chance of inheriting both mutations necessary which is necessary for the disease to be manifest. Mutations in at least 3 genes seem to be responsible for type II disease.
Pedigree
Autosomal recessive
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
Diagnosis and Prognosis
Most patients live productive lifestyles and have a normal lifespan. Hearing aids are useful and speech therapy early can aid in the development of normal speech. Many young children have near normal speech and the diagnosis may be missed if no family history of Usher disease is present. However, once the diagnosis is made, it is useful to monitor hearing as some progression occurs and some older patients with severe loss can benefit from cochlear implants.
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