Hearing loss that is inherited through genetics and has its root cause in the vestibulocochlear nerve, the inner ear, or central processing centers of the brain is the most common sensory impairment in humans. In fact, 1 in 500 newborn babies and an estimated 278 million people around the globe have moderate to severe hearing loss, with 185 million of those cases being inherited.
Luckily, modern genetics is very good at determining if people losing their hearing have mutant genes responsible for the ailment. Unluckily, there are 54 known genetic mutations that can cause deafness, and some of them are nastier than others.
For example, babies born with Usher Syndrome only show signs of deafness at an early age. But by age 10, they become blind as well. Knowing that kids have this and other genetic mutations can help parents prepare themselves and their children for these eventualities. Additionally, some hearing loss genetic defects can be mitigated through aversion to sunlight or vitamin therapy, for example.
The problem with determining exactly which genetic mutation is at fault – if any – is that these tests must be run on a gene-by-gene basis in order to be accurate, and can take up to a year per test. And it’s not cheap. Since there are so many known genes to test, this can cost up to $75,000.
Researchers at the University of Iowa in collaboration with the Baylor College of Medicine have developed a new test called OtoSCOPE that covers each and every genetic mutation at once. This one single run takes just three months and only costs around $2,000.
There are two developments in technology that have allowed this to happen. One is the ability to enrich specific regions of the entire genome rather than having to remove and test certain sections one at a time. The second is new technologies in genetic testing that allows for many different samples to be analyzed at once and at record speeds. Specifically, they used both a 454 GS FLX pyrosequencing machine and Illumina GAII cyclic reversible termination sequencing machine.
To make sure that these techniques worked, senior author Richard Smith, Sterba Hearing Research Professor and vice-chair of otolaryngology at the University of Iowa, tried the new test on 10 patients. Three were deaf and already knew which genetic defect was the cause. Another six were deaf but did not know which gene was to blame. The final three could hear just fine.
The test worked beautifully. Not only did it correctly identify the three known patients’ defects, nail five of the six unknown causes and ignore the three healthy subjects, it also identified three previously unknown genetic mutations that cause deafness. These new genes – and many more that have yet to be discovered – can be easily added to the test for future patients.
Smith and his collaborators believe that OtoSCOPE will be available for clinical use by the spring of 2011.