Usher Syndrome Type I
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
Type I Usher syndrome accounts for the majority of cases and is arguably the most severe form of the disease. Deafness is profound from birth. Many children never learn to speak unless they are outfitted with cochlear implants at an early age. Balance is impaired as well since the vestibular apparatus in the inner ear is also affected. Consequently, young children often do not walk until 18-24 months of age and sitting alone is delayed as well. Athletic prowess is permanently impaired. The light-sensing cells of the retina are also involved leading to nightblindness by the second decade of life and progressive deterioration may lead to blindness in adults. Side vision progressively narrows and severe ‘tunnel vision’ results. Some individuals have cognitive deficits and may be mentally retarded. Some have psychotic symptoms.
Genetics
Inheritance
Usher syndrome is an autosomal recessive disorder in which the carrier parents are normal. However, offspring of such parents have a 25% risk of inheriting Usher syndrome. Mutations in at least 7 genes have been identified as causative.
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
Auditory testing can detect deafness at birth but this is often missed in the absence of a family history. Of course, other causes of deafness (infections, birth defects) must be ruled out before the diagnosis of Usher syndrome can be made, and this may require gene testing. The visual problem is not present at birth but an eye examination in young children may detect early signs of retinitis pigmentosa. Speech therapy and visual aids are recommended.
The prognosis for life is good. Hearing aids are usually of little benefit and therefore cochlear implants should be considered to enable speech to develop. The balance difficulties, tunnel vision, and nightblindness create special problems in sporting activities and carrying out normal tasks, especially at night. Swimming requires special precautions due to the risk of disorientation under water.
Web Resources
Printer Friendly Version: Ctrl/Cmd+P