Gene mutations can cause hearing loss in several ways.
Genetic factors make some people more susceptible to hearing loss than others. Their genes make them more predisposed to hearing loss due to ageing or induced by noise, drugs or infections. It is estimated that the causes of age-related hearing loss are 35-55% genetic.
Genes in ear cells affect our hearing
Genes are chemical units found inside all cells of the human body. Inside the cell the genes form specific structures called chromosomes, which make up our DNA and hold our hereditary characteristics. Every cell in the human body is composed of some 30,000 genes.
Some of the genes in ear cells affect our hearing and help determine how sounds are turned into signals that the brain understands.
At times, changes occur in the DNA of the genes, affecting their functioning. If these mutations occur in a gene with important information about our sense of hearing, the result may be hearing loss or, in extreme cases, deafness.
Examples of hereditary hearing loss causing hearing impairment include Otosclerosis, Usher's syndrome and Pendred syndrome. You can find more specific information about different syndromes under "syndromes of hearing loss".
Inner ear sensory hair cells play a vital role in our hearing, and mutations in these cells can prevent them from functioning properly, resulting in hearing loss.
Finally, gene mutations may cause several non-hearing related, hereditary conditions combined with a deformation of the inner ear, resulting in deafness at birth or later in life.
Inherited from parents
All human genes exist in two copies passed on from the mother and the father, respectively. The risk of hearing loss may depend on whether a possible mutation is dominant or recessive. A dominant mutation causes hearing loss if just one of the inherited copies from the parents is damaged. Recessive mutations manifest themselves as hearing loss only if both copies are damaged, i.e. if both parents are carriers of the gene mutation.
Different types of hearing loss
Pinpointing the genetic causes for a specific hearing loss is complicated. Many different genes can cause the same type of hearing loss and the same genes can also be involved in different types of hearing loss. Two people with the same gene mutation may still have very different levels of hearing ability.