The three most common causes of hearing loss are age, environmental factors and genetic factors.
Most people experience some degree of hearing loss between the ages of 30 and 40, and almost all by 80. Repeated exposure to noises such as loud music and factory machinery can damage the ears over time, while one loud noise such as an explosion can result in instant damage – it’s one reason that so many people serving in the armed forces suffer (3,500 out of 156,000 according to an FOI request in 2014).
Between 50-60% of hearing loss in infants can be put down to genetic factors, and when one considers the complexity of life, building a human from just a few cells it is perhaps not a surprise that the percentage is so high – three in every 1,000 babies born. The hearing loss might be due to a blockage or disorder in the bones, known as conductive hearing loss, or sensori-neural hearing loss occurring when the hair cells in the cochlea or auditory nerve are damaged.
The statistics of genetic hearing loss can be broken down further. Around three quarters of cases of deafness in children are the result of inheritance by recessive genes, while 20–25% of inheritance is due to inheritance of dominant genes. A few other cases arise as a result of other genetic factors.
Without this knowledge one might imagine that two deaf parents would almost certainly create a deaf child, but this explains why this is not the case – if the gene for deafness is passed on in recessive form, it might not be expressed in the child.
While a lack of hearing loss is obviously good for the child an upbringing by deaf children might be slightly different, as they cannot hear their child crying or being naughty. Babysitters or day care providers might be surprised at the volume of crying from a child who has grown up in an environment where their demands cannot be heard. And as a final note genetic deafness might skip a generation – meaning that an unlucky person might have deaf parents and children, despite suffering no hearing loss themself.
Statistically 70% of mutations causing hearing loss are non-syndromic, which means that it is an issue in its own right as opposed to being one abnormality within a wider syndrome.
But there are more than 400 genetic syndromes where hearing loss is a possible characteristic. Down’s Syndrome is one of the more common ones, and according to Sense somewhere between 40 and 80% of people with the syndrome – caused by an extra chromosome – have some form of hearing loss. Around 750 people with the syndrome are born in the UK each year, and may also suffer from eyesight and heart problems, alongside learning disabilities.
Another genetic syndrome where hearing loss is common is Usher Syndrome, which is a leading cause of deafblindness – affecting 1 in every 23,000 people in the US. Treacher Collins Syndrome affects the bones and tissues in the face and can sometimes cause ears to be small or completely absent, with possible defects in the bones in the middle ear. Around 1 in every 50,000 people is affected, and half of them may suffer from hearing loss.
Other syndromes in which deafness is a possible characteristic include Waardenburg Syndrome (1 in 40,000 people), Stickler Syndrome (1 in 7,500-9000 people) and Alport Syndrome (1 in 5,000 people).
Most of these syndromes and genetic abnormalities can be established before birth through genetic testing and/or amniocentesis, so the parents are at least psychologically prepared.
Further related news comes from Biomedical Research company Novartis Institutes. Bloomberg reports that the Switzerland-based company is trialling a gene therapy that they hope will stimulate the regrowth of damaged or lost ear hairs, and could give people their hearing back. Unfortunately it will not work for all of those with genetic hearing loss as the genes have to be initially present to be stimulated for the technique to work – but it is still cause for excitement in the industry.