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In 1990 the cost to Britain of Alzheimer's disease was estimated at up to Pounds 3 billion a year. There is no reversing this cruel illness, which robs sufferers, literally, of their minds; the medics' best hope is to slow the process of neural decay with drugs developed to protect nerve cells from dying. But this is only possible if methods are perfected for identifying the disease early - before dementia sets in.

"The problem with trying to identify Alzheimer's early is that there are two other common causes of cognitive deficit in the elderly - the relatively benign cognitive decline caused by ageing and that associated with depressive illness,'' explains David Smith, head of Optima, the Oxford project to investigate ageing. Researchers have now developed brain scanning methods which prove that Alzheimer's is not an inevitable part of normal ageing but a true disease process that may follow a catastrophic event in the brain. This raises fresh hope that effective treatment may be found. "If we could slow down that catastro- phic loss of tissue by even 5 per cent, most sufferers would die of natural causes before suffering the desperate indignity of the loss of their minds," says Smith.

One solution may lie in Hormone Replacement Therapy, best known for its success in maintaining bone density in post-menopausal women. Researchers at Columbia University observed 1,124 elderly women, 968 of whom had not used oestrogen to reduce symptoms associated with the menopause. Over 16 per cent of the HRT-free group went on to develop Alzheimer's, compared with just 5.8 per cent of those taking the drug. Since oestrogen is known to promote the growth of certain brain cells, the hormone may delay the formation of the plaque deposits in the brain that characterise the disease. In men, the brain converts testosterone to a form of oestrogen, so giving men the male hormone may have similar effects.