What is Usher syndrome?
Usher syndrome is named after the British eye surgeon who first described it in 1914. It is a rare, inherited disorder that causes deafness and gradual vision loss. It can also affect balance.
Scientists have identified 3 types of Usher syndrome (1, 2 and 3). Babies with Usher syndrome are born deaf or hard-of-hearing. The vision loss develops during childhood or adolescence.
The different types of Usher syndrome are divided by the degree of hearing and vision loss, the age when vision loss occurs and how quickly it progresses, and whether balance problems are present. Within the three main types of Usher syndrome, there are individual differences in symptoms and how quickly the condition progresses.
How common is Usher syndrome?
The National Institutes of Health reports that 3% to 6% of all children who are deaf and 3% to 6% of children who are hard-of-hearing have Usher syndrome. In developed countries such as the United States, about four babies in every 100,000 born have Usher syndrome.
What are the different types of Usher syndrome?
Type 1 and type 2 are the most common forms of Usher syndrome in the United States. These 2 types account for about 95% of all cases of Usher syndrome.
Babies born with Type 1 Usher syndrome:
- Are almost totally deaf at birth.
- Have severe balance problems.
- Sit without support at a later age than normal (normal is at 6 – 9 months old).
- Are late walkers (18-24 months).
- Develop vision problems before age 10, usually in early childhood.
- Begins with night vision problems.
- Progresses quickly to total blindness.
- May not benefit from hearing aids (devices that make sound louder). They may be candidates for cochlear implants (a surgically placed device that sends sound directly from ear to stimulate the hearing nerve).
Babies born with type 2 Usher syndrome:
- Have moderate to severe hearing loss at birth.
- Have normal balance.
- Can benefit from hearing aids.
- Develop night vision problems as teenagers.
- Progresses more slowly.
- Does not result in total blindness.
Babies born with type 3 Usher syndrome:
- Have normal hearing at birth.
- Have almost normal balance.
- Sometimes have balance problems later on.
- Have gradual hearing and vision loss.
- Rate of loss differs among children.
- Hearing loss is apparent by teens.
- Can benefit from hearing aids after hearing loss begins.
- Night blindness starts in puberty.
- Blind spots occur by late teens/young adulthood.
- Total blindness by middle age.
What causes Usher syndrome?
Scientists now know that Usher syndrome is inherited, which means it is passed from parents to children, and is caused by changes, called mutations, in genes. Genes are the chemically coded instructions in cells that tell cells what to do. The human body contains 20,000 to 25,000 genes. Every person has two copies of each gene, one from each parent.
Usher syndrome is an autosomal recessive disorder. This means:
- Males and females can both be affected by the condition.
- Both parents carry a mutated gene but do not have Usher syndrome themselves.
- A baby can get either the mutated gene or the normal gene from each parent.
- A child who gets a mutated gene from each parent will have Usher syndrome. The chance that a child from two parents who each have an Usher gene will have Usher syndrome is 1 in 4.
What causes vision loss in Usher syndrome?
The retina is a tissue at the back of the eye that is needed for vision. The gene mutation in Usher syndrome affects the retina's light-sensing cells called rods and cones. This condition is called retinitis pigmentosa or RP.
In RP, the retina's light-sensing rods and cones slowly go bad, starting at the outer edges. As RP gets worse, the person loses peripheral (edges) vision first then central vision.
What causes hearing loss in Usher syndrome?
The cochlea is a spiral structure in the inner ear that transmits sound. In Usher syndrome, the gene mutation affects the nerve cells in the cochlea so they do not transmit sound normally.