MORE than half of us become deaf with age, part of the ''sans everything'' syndrome which affects the over-60s. Loss of hearing does not happen, however,

simply because our ears wear out, even though many married men would maintain this was a scientifically proven fact.

The incredible mechanism which brings us the pleasure and pain of sound is governed by a range of genes, and new American research with mice has made a start on isolating them. Applied to humans, this miracle of genetic

science could, some years down the line, not only help babies born profoundly deaf to hear, but could also be instrumental in slowing hearing loss as we grow older.

According to Andy Irvine, of the Council for the Advancement of Communication with Deaf People, the deaf are not required to register as the blind do, but the Royal National Institute for Deaf People (RNID) estimates that there are about 8.7 million deaf and hard of hearing people in the UK. Of the 730,000 people in Scotland suffering from all degrees of deafness, 528,000 are over 60.

That figure is rising as the over-60 population increases, but the number of children who are prelingually deaf (the 13 in every 10,000 children who are deaf before developing language) has remained static for the past 20 years. Rubella vaccination means there are fewer babies born deaf as a result of their mothers having had German measles during pregnancy, but this drop has been offset by more babies being born deaf from other causes.

Professor Karen Steel, of the Medical Research Council's Institute for Hearing Research in Nottingham, says the current American research is aimed at helping severe childhood deafness, but explains that people suffering from other forms of deafness may benefit

in the long term. Although illness or excessive noise might appear to be the cause of the loss of hearing in

older people, there is usually a genetic pre-disposition to deafness. Even the baby who loses its hearing because

of rubella probably also carries a faulty gene.

It is the identification of the faulty genes that the hearing experts are getting so excited about. With the customary caution of the researcher, Professor Steel says: ''If and when there is a breakthrough, it could be that several genes are involved, and that will just be the start of the research into what those genes are doing to the ear.''

Treatment evolving from such research would, she believes, be some five to 10 years away.

For the lay person, the question is, what are these genes doing at all, not what are they doing to the ear. With great patience, Professor Steel explains that each gene is coded for a protein which has a job of work to do. Sometimes there is a mistake, and the protein will not be able to function properly, and so a particular part of the body goes wrong. Most of the deafness genes are coded for proteins in the

ear, and when they go wrong, the ear can't work.

Explaining the technical terms, Professor Steel says a recessive gene is

one where two copies of a defect are needed to cause a problem. Only one copy of an abnormal gene is needed to cause a problem in what is described as a ''dominant'' gene. We inherit deafness because somewhere along the line, a bad copy is made of one of the many genes involved in hearing.

At the British Deaf Association, they are ''cautiously excited'' by the American researchers' latest findings. Today, however, the spectre of genetic engineering must hover over any such discoveries, and a spokeswoman points out that while members of the association feel it would be helpful if parents could find out through gene identification that their baby would be deaf and so prepare for it, no-one is against a baby being born deaf. Professor Steel is only too aware that the issue is an emotive one, and although she believes that almost every parent would want a normally hearing child, she is quick to reassure that her research is to enable professionals to be able to treat the child who is already deaf.

''Pre-natal diagnosis and selective abortion is absolutely not the aim of my research,'' she stresses, explaining that this sort of scenario is unlikely to ever be on the cards because most children born deaf ''pop up out of the blue''. With no prior deafness in the family, there would be no reason to look for it pre-natally. ''The idea of identifying genes which cause deafness is to get a better idea of the biology of the ear, which we know very little about now,'' she says. So, successful treatment, not eugenics, is the name of the game.

While that treatment is still in the realms of science fiction, Professor Steel suggests that we all offset any genetic pre-disposition to deafness by looking after our ears. The cells lost at the age of 14 at a rave, she warns, will never regenerate.