Usher Syndrome is a genetic condition, caused by an autosomal recessive gene. Most people with Usher Syndrome are the only ones in their families with the condition although some families do have more than one affected child. In fact, in many families no one else had either a hearing loss or RP. So how can this possibly be inherited?

We inherit much from our parents via genes. Each gene has a different function, one may determine what colour of hair we may have or another may determine whether we have curly or straight hair. Some traits need two or more genes working together. For example, your height is determined by several genes, as well as by diet and general health levels throughout childhood.

What happens in a 'genetic condition' is that the gene that carries out a particular function is either missing or not working correctly. An abnormal gene sends the wrong message to the body, and the body part that the message is sent to is unable to function correctly. Some genes are called 'dominant' genes, and some are called 'recessive' genes. Dominant genes always prevail.

Many conditions are the result of a recessive gene, cystic fibroses is one of the most common.

Usher Syndrome is caused by one of the recessive genes. If a man and a woman each have a pair of unmatched genes, one is a dominant gene, and the other is a recessive Usher gene. As they each have a dominant gene their eyes and ears work correctly, and they have no idea they 'carry' the Usher gene. If this couple have children each parent will pass either the dominant or recessive gene onto the child. They each cannot give both genes or else the child would receive twice the usual number.

If both parents give their child the dominant gene then the child will have normal hearing and vision and have no Usher gene. If the father gives the dominant gene and the mother gives the recessive gene, then the child would be like the parents with normal hearing and vision. The same happens if the mother carries the dominant gene. However, if both the father and mother give the recessive Usher gene then this is the only time the Usher condition appears.

So, there are four possible combinations:

1. Dominant with dominant
2. Dominant with recessive (a carrier)
3. Recessive with dominant (a carrier)
4. Recessive with recessive (Child will have Usher)

Therefore two carriers have a 1 in 4, or 25%, risk of each child conceived being born with Usher Syndrome.

It is not until two carriers have a child with the recessive-recessive combination that it becomes obvious that the gene was even in the family.

If two people with Usher Syndrome have children, then all of their children could also have Usher Syndrome if the parents both have the exact same pair of recessive genes (eg. both on the long arm of chromosome number 11). Every child will receive two recessive genes.

The Usher parent gives a recessive Usher gene and the other parent gives a dominant gene. All the children will be carriers of Usher Syndrome.

The carrier parent will either give the dominant gene or the recessive gene while the Usher parent gives a recessive gene. Therefore, there is a 50:50 chance that the child will have Usher Syndrome or the child will be a carrier.

At least three types of Usher Syndrome are known at present. Different genes cause each type. So far we know that at least three genes cause Usher Type 1 (people born deaf) and are located on the long and short arms of chromosome number 11 as well as on the long arms of number 14. Type 2 (people born hard of hearing) is located on the long arm of chromosome number 1 and another locus will undoubtedly be found. Type 3 (people with a progressive loss of hearing) is located on the long arm of chromosome number 3.

None of their children would have Usher Syndrome as they have two different Usher genes. The person with Type 1 would have a normal gene at the Type 2 location and vice-versa. The children ought to be carriers for both types but do not actually have Usher Syndrome. The same is true for a person with Usher Type 1 who has the gene on the short arm of chromosome number 11 and has a child with someone with the gene on the long arm of chromosome number 11.