Hearing Loss and Genetics
 

     With 15% of Americans over age 18 (37.5 million people) experiencing some trouble hearing, hearing loss is an exceedingly prevalent ailment that becomes more likely with age. Over recent decades, it has becoming increasingly understood that genetics play a major role in many cases of hearing loss, both age-related and not.
     Our knowledge of human genetics has grown substantially in the last two decades, thanks to advances like the Human Genome Project that have allowed mapping of the entire human genetic code (genome). Many large scale “biobanks” – huge repositories of genetic information from many patients, in the form of biologic samples (blood and tissue) – have been developed, including the UK Biobank and our own Penn Medicine BioBank. These research initiatives have allowed the collection and categorization of genetic samples from individuals with a wide array of disorders, in order to facilitate research efforts into the genetic causes of and contributions to diseases. 
     In hearing loss, the role of genetics can be variable. For children born with hearing loss, genetic causes can be identified a large proportion of the time. On the other hand, hearing loss from some causes – like loud noise exposure – seem to be clearly the result of environmental factors. Yet even so, in the latter case, an individual’s genetics may play a greater role in determining susceptibility to hearing loss as a result of noise exposure than we may have previously thought. In middle-aged and older adults, individual genetics likely underpin susceptibility to hearing loss and interact with a variety of environmental factors to determine the development of hearing loss, including its type and severity. 
     Identifying the role of genetics in hearing loss – including specific causative genes and how they interact with environmental factors (such as medications and noise exposure) to cause hearing loss – is an important pursuit for several reasons. First, in families with multiple members with hearing loss, identifying a gene in one individual may enable prediction of the development of hearing loss in others who possess the same gene variant. Second, we may come to recognize that specific genes portend different hearing loss prognoses, such as whether the loss will be mild or severe, stable or progressive. This could result in more personalized management for individuals with hearing loss. For those who receive cochlear implants, we could even use genetics to predict who is more likely to get a good outcome with the implant.
     Identification of the multitude of genes that can cause or contribute to hearing loss can help to pave the way for the development of individualized gene therapy for hearing loss – a goal that seems futuristic but may be achievable in our lifetimes. Gene therapy would involve the delivery of a functional copy of the nonfunctional gene in order to restore hearing. Several studies have been underway for years, testing gene therapy for hearing loss both in cells and in animals. While results are promising, there is work to do yet. Still, genetics research is a vital part of the development of gene therapy that could help members of our or future generations with hearing loss. 
     For more information about the Genetics of Hearing Loss program at Penn Medicine, follow the link below.

https://www.pennmedicine.org/for-patients-and-visitors/find-a-program-or-service/ear-nose-and-throat/general-audiology/genetic-analysis-for-adul-onset-hearing-loss

Alexandra Quimby, MD MPH
Fellow, Neurotology
Department of Otorhinolaryngology - Head & Neck Surgery