Genetic researchers in Germany believe their research will lead to better ways to diagnose Usher syndrome. This condition causes up to ten percent of all cases of deafness in children and 50 percent of combined deafness and blindness in adults.
Usher Syndrome Defined
Approximately 10,000 to 15,000 people in the United States have Usher syndrome, which is a combination of deafness and blindness. There are three basic types of Usher syndrome:
• Type 1 causes deafness at birth and progressive vision loss from retinitis pigmentosa as early as age five.
• Type 2 causes moderate to severe hearing loss at birth which progresses to deafness. Vision can be near normal at birth but progresses slowly toward blindness beginning in the teens.
• Type 3 patients are born with normal hearing and vision but begin to lose both senses by about age 20.
Recessive Genes Defined
Usher syndrome has long been considered to be an autosomal recessive condition. This means that the condition is inherited and is caused by a mutation to a gene that is recessive, or non-dominant. During conception, a child receives one-half of her genes from her mother and the other matching half of her genes from her father. In order to function, both halves of each gene must be present.
Each half of a gene pair can be either dominant or recessive. If a gene is dominant, it is going to “win” over a recessive gene in controlling whether that trait shows up in the new baby or not. In the case of Usher syndrome, we can call a normal, dominant gene a “good” gene. The genetic mutation that causes Usher syndrome, which is a recessive or “submissive” gene we will call a “bad” gene.
If each parent gives the baby a good gene, her gene pair will be normal and she will not have Usher syndrome. If one parent gives her a good gene and the other parent gives her a bad gene, the good gene will overpower the bad gene and she will not have Usher syndrome. But if both parents give her a bad or recessive gene, there is no good gene present to overpower them and she will have Usher syndrome.
New research into Usher Syndrome
This is a very simplistic way to talk about a very complicated process. Research has shown that there are several genes that must all be recessive in order for a person to have Usher syndrome. Dr. Hanno Bolz, Associate Medical Director of the Bioscientia Centre for Human Genetics in Ingelheim, Germany said his team is working to better understand how genetic mutations cause Usher syndrome (USH). New studies show that some patients with USH have only one “bad” copy of a gene believed to contribute to Usher syndrome. This does not make sense based on current knowledge of how recessive genes normally work. Bolz also cited unexplained variations in the visual characteristics of the disease between close family members. A disease that is inherited is usually very similar in close family members.
Bolz and fellow researchers are working on ways to study several genes at the same time, as well as studying genes that produce other proteins that are similar to the ones affected in Usher syndrome. They hope to pinpoint genetic variations that can cause Usher syndrome as a tool in providing earlier diagnosis of the disease.
Currently, USH is not diagnosed until both hearing and sight are affected. When research on the genetic cause of Usher syndrome can be turned into a functional genetic test for the condition, parents will have a valuable tool to help them make the best choices about how to treat early deafness in their children. Knowing at a young age that a child may also lose vision may change how hearing loss is treated and will give eye doctors advanced notice to watch for early symptoms of retinitis pigmentosa.
Sources:
Science Daily
Hear See Hope: Usher Syndrome Foundation
National Institutes of Health: Office of Rare Diseases Research