April 2019 Korea Biomedical Review
Researchers at Seoul National University Bundang Hospital have developed a new protocol for screening specific genetic variants in congenital auditory neuropathy. In Korea, congenital middle ear deafness affects 1 out of 1,000 newborns, while 8 percent of those newborns suffer from auditory neuropathy. Auditory neuropathy is a disorder that causes hearing loss due to problems in the process of transmitting the sound which enters through the inner ear to the brain. As of now, there are many difficulties in choosing the appropriate treatment method and predicting the treatment outcome as there are various causes and patterns. In particular, although cochlear implantation has received much attention as it is the only surgery that can restore hearing in auditory neuropathy caused by OTOF gene mutation, there are limitations in the early diagnosis and treatment of the OTOF gene mutation in the Korean population.
To resolve such limitations, the team, led by Professor Choi Byung-yoon of the department of otorhinolaryngology at the hospital, confirmed the types and ratios of OTOF gene mutations through genealogy and nucleotide sequence analysis for patients diagnosed with auditory neuropathy. The study showed that 90.9 percent of local auditory neuropathy patients have mutations in the OTOF gene. “Auditory neuropathy patients may have residual hearing, while sometimes the symptoms heal itself, making it difficult to determine the appropriate time for surgery,” the team said. “If an OTOF mutation that accounts for a large proportion of auditory neuropathy is discovered in a patient, it may help doctors decide on cochlear implant surgery sooner.”
According to the team, however, one of the problems which limited the medical professionals from finding the OTOF mutation is the next-generation sequencing method as it may not be able to detect specific mutations in the OTOF gene commonly observed in patients with congenital auditory neuropathy, which may delay the cochlear implant surgery. To overcome such limitations, the researchers proposed a new protocol for diagnosing mutations based on genetic analysis. The new protocol was able to detect variations in auditory neuropathy patients by performing direct sequence analysis on seven OTOF variants found in local auditory neuropathy patients.
The study also compared the degree of hearing recovery according to the time of cochlear implantation in patients with auditory neuropathy. The group that received the transplantation before 18 months scored 4.2 points in the hearing performance test performed six months after surgery, whereas the group that underwent surgery after 18 months scored 1.5 points.
“In the future, proper genetic testing to identify congenital auditory neuropathy will allow for early detection of OTOF mutations,” Professor Choi said. “It is important for parents who have a baby suffering from congenital hearing neuropathy to take the genetic test as it can help the recovery process.”