Have you been told that Usher syndrome Type 3 and Type IF Carrier testing runs in your family?
Usher syndrome is a relatively common genetic disorder that affects hearing and sight. Hearing loss is probably the most recognizable symptom, but retinitis pigmentosa, a disorder of the eye, can eventually cause partial or total blindness. No cure exists for Usher syndrome. However, genetic testing can provide a definitive diagnosis so the condition can be managed.
What Is Usher Syndrome?
Medical experts divide Usher syndrome into three classifications and several subdivisions. The types are numbered one through three. A diagnosis is placed in one of the categories depending upon the age at the onset of symptoms.
Scientists have studied the symptoms of Usher syndrome since the middle of the 19th century. It was not until 1914 that C.H. Usher, an English ophthalmologist, published a study of the syndrome in which he explored the idea that the disorder was inherited. From those beginnings, researchers have discovered eleven genes which are involved in Usher syndrome. The type of the syndrome is determined by which mutated genes are inherited.
In general, the genes that are connected to the disorder are responsible for producing proteins that help with hearing, vision and balance. Because these genes are damaged or altered, the person who inherits them has difficulty with many everyday activities. However, Usher syndrome does not adversely affect life expectancy.
Symptoms of Usher Syndrome
Babies who are born with the syndrome are diagnosed with type I. Their hearing loss is profound. Retinitis pigmentosa begins to damage the ability to see early in the child's life. With this form of the disease, it's common to see abnormal development of the vestibular system. This means that sitting, walking, riding a bicycle and other activities can all be difficult.
Type II of the disorder may involve some hearing loss at birth, but the vestibular system typically develops normally. This means that children with type II do not generally have balance issues. Still, hearing loss can progress throughout childhood and into adulthood. Vision loss is progressive and often begins at adolescence or in adulthood.
People with type III Usher syndrome first develop symptoms later in life. Hearing ability may be normal at birth but begin to deteriorate in adolescence, as does vision. Some people may experience profound hearing and vision loss by the time they are middle aged.
Genetic Testing for Usher Syndrome
Scientists know of at least eleven genes that may be responsible for causing Usher syndrome, and they believe it's likely that others also may be involved. Because there are so many possibilities, genetic testing for abnormalities in these genes is not routinely performed. Nonetheless, people who have a family history of the disorder may want to find out if they are carriers.
Usher syndrome is classified as an autosomal recessive trait. This means that it can occur in either males or females. Both sexes can be carriers, and both could be affected with the disorder. Because it is recessive, both parents must have a mutated Usher syndrome gene in order to have a child who is affected by the syndrome. Currently, it is not possible to test to see if prospective parents are carriers of some of these mutated genes. However, it is possible to test for mutated genes that will cause type 1F and type III of the syndrome. This means that it may be critical for people with a family history of Usher syndrome to be tested by submitting a blood sample.
Genetic testing for Usher syndrome on an infant or young child can also answer many questions. With a definitive diagnosis, it is much easier to move forward with management of the condition.
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