Explore Causes of Hearing Loss in more detail :
Genetic Hearing Loss
Genes are small structures which can be found inside many of the cells of our body which determine our individual characteristics. Genetic hearing loss simply means any hearing loss that is known to be caused by a genetic factor, as opposed to an environmental factor, such as infection. Sometimes genetic hearing loss is identified by undertaking chemical analysis taken from blood samples, while in other cases it can be identified through a detailed family history. When a genetic hearing loss is identified in combination with other disabilities, and there is known single genetic cause for those disabilities including the hearing loss, the cause is said to be a “syndrome”. Genetic causes of hearing loss can therefore be divided into “syndrome” and “non-syndromic”. You can find more information about syndromes that are associated with hearing loss (and the definition of what a syndrome is) in section SoundSpace Online - Syndromes, while the rest of this section focuses on non-syndromic genetic hearing loss.
Types of genetic inheritance
Any genetic condition can be classified either by the way it is inherited, in particular whether both parents or just one carry the gene that causes the condition. This is particularly important for families when thinking about, for example, having another child or whether other children should be tested. “Recessive” hearing loss means that the gene causing the hearing loss can only be passed on if both parents carry that gene. When this happens, each of the couple’s children has a 25% chance of having the disorder, a 25% chance of being free of the gene itself (e.g. not a carrier of the gene) and a 50% chance of carrying the gene but without being affected by the condition (in this case hearing loss). By contrast, “dominant” genetic conditions can be passed on by just one parent.
Identifying specific genes that cause individual hearing loss
The other approach is to figure out the exact genetic mutation by undertaking blood tests. The focus of the second is to identify genetic mutations, a permanent change in the sequence of proteins which make up DNA. There are a number of genetic mutations which are known to cause non-syndromic hearing loss. The single most commonly identified genetic mutation of this type is a mutation in the GJB2 gene, which is responsible for making the protein Connexin-26. a protein which is necessary for the survival or function of the tiny “hair cells” which help the inner ear respond to sound (see below right picture for the connexin cell). Children born with a mutation in this gene therefore have missing or non-functioning hair cells and therefore permanent sensorineural hearing loss.
There are thought to be around 400 different genetic causes for hearing loss but Connexin 26 accounts for fully a third of all cases of genetic hearing loss. Please visit this Boys Town website page for more information on genetic hearing loss. Another relatively common genetic mutation is GJB6, which is responsible for making the protein Connexin-30.