The Harvard Medical School Center for Hereditary Deafness (HMSCHD) seeks to understand, diagnose, and treat hereditary hearing loss in humans. It does so by coordinating activities of scientists and clinicians at Harvard Medical School and Harvard Affiliates in gene discovery, molecular diagnosis, therapeutic development, patient education, and training of physicians and scientists.
How We Hear
Sound enters the ear and is converted into vibration by tiny cells. The vibration of these cells is then converted into an electrical signal, which the brain can understand.
The outer ear carries sound into the ear drum, middle ear, and then finally the inner ear, which hosts the cochlea, the organ that converts vibration into a neural signal. This signal is then carried by the auditory nerve to the brain.
To learn more about how hearing works, watch the above video.
Hearing is a complex process, so it should be no surprise that the causes of hearing loss are also complex. Hearing loss can occur because of damage to the ear, especially the inner ear. For example, infants may be born with hearing loss caused by a viral infection that was acquired during pregnancy. At other times the cause is genetic and therefore due to changes in the genes involved in the hearing process. Sometimes, hearing loss is due to a combination of genetic and environmental factors. There is, for example, a genetic change that makes some people more likely to develop hearing loss after taking certain antibiotic medications. Understanding the genetic causes of deafness has important benefits. This knowledge not only allows doctors to inform families about their chances of having children with hearing loss, but it can also influence the way a person’s deafness is treated. Whether a person’s hearing loss is going to worsen can sometimes be predicted if the specific cause is known. Also, deafness may be only one of a group of medical problems that a person may have. For example, some people with hearing loss also have problems that affect other parts of the body, such as the heart, kidneys, or eyes. Knowing the genetic cause in these cases allows a doctor to be aware that there might be problems in other systems as well. It might seem reasonable to suspect a genetic cause of deafness only if the hearing loss runs in the family. But it is common for children to have genetic deafness even though neither one of their parents are affected. This deafness can also be passed on to future generations. Genetic tests can therefore be helpful even if there is only one person in the family with hearing loss. The genetics of hearing loss can be complicated and difficult to understand. This booklet is designed to help explain the role of genetics in hearing loss, how genetic testing is done, what the results of genetic tests mean, and what options are available for treatment and counseling. For more information, please refer to the online booklet, "Understanding the Genetics of Deafness A Guide for Patients and Families", or ask your physician or your child’s physician.