Your genetic make-up
We know that there are 28,000 different genes, but we don't know exactly what each of them does.
We know that some genes have an impact upon hearing and deafness. But we need to know more about these genes, and we need to keep finding other genes that play a role in hearing loss. This will help us develop new treatments in the future.
Once scientists know which protein is coded by a deafness gene, they can find out what the protein does in a normal ear, and investigate how its function is affected by genetic mutation.
This understanding will form the basis of research into drug treatments - or perhaps even genetic therapy. But these developments take a lot of hard work and won't happen overnight. This is where we come in. We exist to fund research into deafness and hearing loss, with a view to curing these conditions. There are lots of different ways to support our work.
How many people are affected by inherited deafness?
In the UK, about one in every 850 children is born with significant sensorineural (ie relating to the inner ear) deafness. Half of these children's deafness is caused by genetic faults passed on from parents.
In around 70% of cases of inherited deafness there are no other accompanying medical problems. In around 30% of cases the hearing problems exist alongside other medical problems.
Genes often play a role in hearing loss later in life. In fact, most of the cases of human autosomal dominant deafness show progressive hearing loss.
How are genetic conditions passed from one generation to the next?
Genes come in pairs. When having a child, each parent passes on one gene from each pair to the child. These two genes - one from each parent - are then combined in a pair of genes in the child.
There are four main ways that genetic hearing loss can be passed on.
The most common mode of inherited deafness is autosomal recessive, which accounts for around 75% of all cases. Autosomal dominant genes account for about 25% while linked and mitochondrial genes only account for about 1% of cases.
1) An autosomal dominant gene
The parent has a 50% chance of passing on the hearing loss to his or her child if they have an autosomal dominant gene.
They have a 50% chance of passing on the single dominant gene to their child. If this happens, it can cause a genetic hearing loss in the child.
2) An autosomal recessive gene
A recessive mutation will not become apparent unless both genes in the pair carry the fauly.
Only when both parents carry the same recessive gene is there a chance of their child being affected by a genetic hearing impairment.
There are three differnet possible outcomes when two autosomal carriers have a child:
- There is a 1 in 4 (25%) chance that the child will receive both hearing loss genes and therefore have a hearing impairment.
- There is a 1 in 4 (25%) chance that the child will receive neither hearing loss gene, and will therefore have normal hearing.
- There is a 2 in 4 (50%) chance that the child will have normal hearing but be a carrier like the parents.
3) An X-linked recessive gene
A woman who carries an X-linked recessive gene has a 50% chance of passing it on to each of her children but how this affects the child will depend on the sex of the child. This is because the X chromosome is a sex chromosome.
- A son who receives the X-linked recessive gene will have hearing loss.
- A daughter who receives the X-linked recessive gene will most likely receive a normal gene for normal hearing on the X chromosome from her father and therefore be a carrier like her mother with normal hearing.
Children of fathers with an X-linked recessive gene will also be affected differently:
- A male with the X-linked recessive gene cannot pass it on to his son because if he has a male child, he must have given his Y chromosome to him.
- A daughter who receives the X chromosome from her affected father will inevitably be a carrier because the father only has the one X chromosome with that gene to give to a daughter.
4) Mitochondrial DNA
Mitochondrial DNA is only passed on by the mother but to all of her children.
A father does not pass mitochondrial DNA to any of his children.