Hearing loss, of which deafness is only one kind, is an impairment or disability involving the function of the ears. Like all other human conditions, it can be caused by factors internal or external to the person or a combination of both. In general, though, the cause of deafness is not known but at present there are reportedly about 400 different types of hereditary hearing loss known.
In the US, for example, while most babies are born with perfect hearing, it is estimated that about 2 to 3 in every 1,000 healthy babies are born with some form of deafness, making it one of the most common birth defects. While this may look genetic in origin, some of these may be caused by infections suffered by the mothers while pregnant. This number of hearing impaired babies may increase as soon as the baby is exposed to such external factors as noise in the environment. Other factors may come into play as the child grows like malnutrition or some infection to the inner ear.
Nadol (1993) reported that an estimated 4 percent of people under 45 years of age in the US and 29 percent of those 65 years or over have a handicapping loss of hearing, while a similar study in Great Britain showed approximately 25 percent of the population questioned had some hearing difficulty . This does not mean, however, that these people have genes for deafness. But it can mean they may have genes with predilection towards deafness when exposed to certain conditions. As of 2013, hearing loss affected about 1.1 billion people .
It is estimated that 50% to 60% of babies born with a hearing impairment have inherited the genes that lead to hearing loss but it is also reported that 25% or more of hearing loss in babies is due to “environmental” causes such as maternal infections during pregnancy and complications after birth . For example, there are some medicines that can cause hearing loss, but only in people who have certain mutations in their genes involved in hearing. One of these genes is one labelled GJB2. Mutations in this gene is now known to be the cause of the most common form of hereditary deafness. Such mutations are found to run in families.
Whether deafness is completely hereditary, however, could be determined after more studies on GJB2 and other genes affecting hearing.
If you think you need a hearing aid, make sure that you get a hearing aid prescription. For more details of our hearing test & assessment, and hearing aid services, please contact HK Hearing & Speech Centre.
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