How Genetic Testing Can Provide a Head Start on Usher Syndrome
Education & Research New advances in genetic testing mean that children and adults with Usher syndrome are being diagnosed at an earlier age than ever before.
Usher syndrome (USH) is characterized by hearing loss that is usually present from birth and a form of blindness called retinitis pigmentosa that usually arises between late childhood to adulthood. Some people with USH also have problems with balance. There are currently at least nine genes known to cause USH.
The problem of diagnosis
Before genetic testing became available, a diagnosis of USH was not made until the retinitis pigmentosa was first noticed. This means that many people who were born with hearing loss were not diagnosed with USH until later in life. Genetic causes of hearing loss are very common. Of the approximately one in 300 children with hearing loss, about half are thought to be due to genetic causes. There are over 80 genes that cause hearing loss, many of them in isolation. However, there are some genes like the ones that cause USH that can have implications for other medical concerns.
“Genetic testing is the only way to make a diagnosis of USH before the onset of retinitis pigmentosa ...”
Genetic testing can now test many genes at once. Since the hearing loss in USH is usually present from birth, genetic testing can provide a diagnosis for young children born with hearing loss years or decades before the onset of retinitis pigmentosa. A review of test results since 2012 in which over 1100 individuals were tested for hearing loss confirmed this. The average age of a genetic diagnosis of USH was 1 year when genetic testing was performed. This is compared to an average age of about 27 years when testing only included the USH genes, since these individuals were already diagnosed with retinitis pigmentosa.
Furthermore, about 4 percent of individuals who underwent genetic testing of hearing loss were given a definitive diagnosis of USH, with another approximately 1 to 2 percent of individuals having an elevated suspicion of USH based on the test results. This is consistent with the conservative estimate that approximately 3 to 6 percent of all childhood hearing loss is due to USH.
Genetic testing is the only way to make a diagnosis of USH before the onset of retinitis pigmentosa, and can provide a diagnosis at an earlier age than ever before. Early diagnosis makes it possible to plan for the future. While there is no cure yet, there are recommendations that can be made.
These include protecting the vision as much as possible, optimizing the acquisition of language, accommodating educational requirements for a child with hearing or vision problems and being aware of safety concerns arising from balance issues, vision loss or difficulty seeing at night. Another benefit to genetic testing is that clinical trials may require knowing the causative gene.
However, limitations to genetic testing still persist. Unexpected or inconclusive results can arise, and therefore anyone undergoing genetic testing should receive appropriate pre-test counseling. Genetic testing may not always provide a diagnosis, but we can expect these limitations to decrease over time as the understanding of human genetics and testing technologies continue to advance.