Usher syndrome type 2A

Other Names: USH2A; USH2; US2 Usher syndrome type 2A is a genetic condition characterized by hearing loss from birth and progressive vision loss that begins in adolescence or adulthood. Vision loss is due to retinitis pigmentosa. Unlike other forms of Usher syndrome, people with type 2A do not have difficulties with balance caused by inner ear problems.

Epidemiology

Usher syndrome affects approximately 4 to 17 per 100,000 people,1,2 and accounts for about 50 percent of all hereditary deaf-blindness cases. The condition is thought to account for 3 to 6 percent of all children who are deaf, and another 3 to 6 percent of children who are hard-of-hearing.

Cause

Usher syndrome type 2A is caused by mutations the USH2A gene. The genes associated with Usher syndrome provide instructions for making proteins involved in normal hearing, balance, and vision. In the inner ear, these proteins are involved in the development and function of specialized cells called hair cells, which help to transmit sound and signals from the inner ear to the brain. In the retina, the proteins contribute to the maintenance of light-sensing cells called rod photoreceptors (which provide vision in low light) and cone photoreceptors (which provide color vision and vision in bright light). For some of the proteins related to Usher syndrome, their exact role in hearing, balance, and vision is unknown.

Most of the gene mutations responsible for Usher syndrome lead to a loss of hair cells in the inner ear and a gradual loss of rods and cones in the retina. Degeneration of these sensory cells causes the hearing loss, balance problems, and vision loss that occur with Usher syndrome.

In some people with Usher syndrome, the genetic cause of the condition has not been identified. Researchers suspect that several additional genes are probably associated with this disorder.

Inheritance

Autosomal recessive inheritance, a 25% chance

Usher syndrome is inherited in an autosomal recessive manner. This means that a person must have a disease-causing change (mutation) in both copies of the gene associated with the syndrome in each cell to have Usher syndrome. One mutated copy is typically inherited from each parent, who are each referred to as a carrier. Carriers of an autosomal recessive condition usually do not have any signs or symptoms.

When two carriers of an autosomal recessive condition have children, each child has a 25% (1 in 4) chance to have the condition, a 50% (1 in 2) chance to be an unaffected carrier like each parent, and a 25% chance to not be a carrier AND not be affected.

Signs and symptoms

Night vision loss begins first, followed by blind spots that develop in the side (peripheral) vision. Over time, these blind spots enlarge and merge to produce tunnel vision. In some cases, vision is further impaired by clouding of the front surface of the eye (cataracts). Hearing loss ranges from mild to severe and mainly affects high tones. The degree of hearing loss varies within and among families with this condition. Unlike other forms of Usher syndrome, people with type 2A do not have difficulties with balance caused by inner ear problems.

For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. 80%-99% of people have these symptoms

• Abnormal electroretinogram
• Hemianopia
• Iris hypopigmentation(Light eye color)
• Nyctalopia(Night blindness)
• Scotoma
• Sensorineural hearing impairment
• Visual loss(Loss of vision)

30%-79% of people have these symptoms

• Cataract(Clouding of the lens of the eye)
• Myopia(Close sighted)

5%-29% of people have these symptoms

• Abnormality of dental color(Abnormality of tooth color)
• Abnormality of dental enamel(Abnormal tooth enamel)
• Anxiety(Excessive, persistent worry and fear)
• Aplasia/Hypoplasia of the cerebellum(Absent/small cerebellum)
• Ataxia
• Carious teeth(Dental cavities)
• Cerebral cortical atrophy(Decrease in size of the outer layer of the brain due to loss of brain cells)
• Depressivity(Depression)
• Hallucinations(Hallucination)
• Microdontia(Decreased width of tooth)
• Nystagmus(Involuntary, rapid, rhythmic eye movements)
• Schizophrenia
• Subcortical cerebral atrophy

Diagnosis

Diagnosis of Usher syndrome involves pertinent questions regarding the person’s medical history and testing of hearing, balance, and vision. Early diagnosis is important, as it improves treatment success. An eye care specialist can use dilating drops to examine the retina for signs of RP. Visual field testing measures peripheral vision. An electroretinogram [e-lec-tro-RET-in-o-gram] measures the electrical response of the eye’s light-sensitive cells in the retina. Optical coherence tomography may be helpful to assess for macular cystic changes. Videonystagmography [vi-de-o-nigh-stag-MAH-gra-fee] measures involuntary eye movements that could signify a balance problem. Audiology testing determines hearing sensitivity at a range of frequencies.

Genetic testing may help in diagnosing Usher syndrome. So far, researchers have found nine genes that cause Usher syndrome. Genetic testing is available for all of them: Type 2 Usher syndrome: USH2A

Treatment

Hearing. Hearing aids are helpful. Young children can benefit from early fitting of hearing aids and speech training to normalize language.

Environmental trauma (e.g., noise) or a genetic susceptibility (e.g., presbycusis) in addition to the congenital, stable deficit of USH2 may combine to produce severe-to-profound hearing loss in older individuals with USH2; in such individuals, cochlear implantation may be warranted. Tunnel vision and night blindness can increase the likelihood of accidental injury.

NIH genetic and rare disease info

• NIH info on Usher syndrome type 2A

Usher syndrome type 2A is a rare disease.

Usher syndrome type 2A Resources
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