Updated April 22, 2015.
Written or reviewed by a board-certified physician. See About.com's Medical Review Board.
About 1 in 500 infants is born with or develops hearing loss during early childhood. Hearing loss has many causes: some are genetic (that is, caused by a baby’s genes) or non-genetic (such as certain infections the mother has during pregnancy, or infections the newborn baby has). A combination of genetic and non-genetic factors also can cause hearing loss. For many babies, the cause of hearing loss is unknown.
One way to describe hearing loss is as “congenital” or “acquired”. Congenital means that a person was born with the hearing loss. Babies born with hearing loss can be identified through a newborn hearing screening test. The test often is done before a baby leaves the hospital in which he or she was born. The screening test does not tell the cause of the baby’s hearing loss. It can tell only whether the baby might have a hearing loss.
Acquired hearing loss means that a person could hear when he or she was born, but developed hearing loss later in life. Acquired hearing loss also can be described by the age at which it starts. If hearing loss starts before the age when children usually begin talking, it is called “prelingual”, which means “before speaking”. If hearing loss starts after the age when children begin talking, it is called “postlingual”, which means “after speaking”.
If the hearing loss gets worse over time, it is called “progressive”. If the hearing loss does not change over time, it is “non-progressive” or stable.
“Syndromic” means that a person has other symptoms besides hearing loss. For example, some people with hearing loss also are blind. There are many different syndromes that have hearing loss as one of the symptoms. “Nonsyndromic” means that the person does not have any other symptoms.
If more than one person in a family has hearing loss, it is said to be “familial”. That is, it runs in the family. If only one person in the family has hearing loss, it is called “sporadic”. That is, it does not run in the family.
The middle ear contains small bones that help send sound from the air to the inner ear. The inner ear changes these sounds into nerve signals that go to the brain. “Conductive” hearing loss is caused by problems in the outer or middle ear. “Sensorineural” hearing loss is caused by problems in the inner ear or in the hearing nerve, or both. “Mixed” hearing loss is a result of both kinds of problems.
Genes are passed from parents to children and cause things to run in families. There are many genes that are involved in hearing. Sometimes, a gene does not form in the way it should. When this happens, it is called a mutation. Some mutations cause syndromic hearing loss and others cause nonsyndromic hearing loss. Even among some families with genetic hearing loss, a loss is not due to mutations in any of the known genes. Scientists are working to find all of the genes involved in hearing loss.
There are also a number of things that are not genetic that can cause hearing loss. For example, babies who are born too early and babies who need help breathing (for example, using a ventilator) are more likely to develop hearing loss than are other babies. Some infections (such as cytomegalovirus) the mother has during her pregnancy can cause the baby to have hearing loss. Also, some infections (such as meningitis) that babies and children have can cause hearing loss.
Sometimes, both genes and environment work together to cause hearing loss. For example, there are some medicines that can cause hearing loss, but only among people who have certain mutations in their genes.
Sources:
National Institute on Deafness and Other Communication Disorders http://www.nidcd.nih.gov/health/hearing/
Early Hearing Detection and Intervention http://www.cdc.gov/ncbddd/hearingloss/index.html
A Parent's Guide to Genetics and Hearing Loss. Centers for Disease Control. Accessed 04/15/2015.
Source...