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Q1: My father suffered from senile dementia in his seventies and I have never been able to establish whether it's something I'm likely to contract? Is there a dementia gene, or could my father have passed on the seed of dementia to me? I'm in my late fifties now and most of the time I convince myself that my forgetfulness is just a product of age. But occasionally I forget things completely and, even if I'm reminded of what happened by someone else, I can't summon up even the slightest hint of a memory. Is there a test I should take or something I can do to ward off dementia? Name and address withheld

A1: Although it has become fashionable to refer to all cases of dementia as Alzheimer's this is medically unsound. Alzheimer's is the most common cause of dementia but there are many others. Estimates of the percentage of patients with dementia who suffer from Alzheimer's varies but it is usually assumed to be around 55 per cent. About 15 per cent have vascular dementia also known as multi infarct dementia, the condition in which the blood vessels of the brain become blocked and this results in a progressive loss of intellectual prowess - the patient in fact has a series of small strokes. In about 12 per cent of cases the dementia is the consequence of a combination of vascular dementia and Alzheimer's, the two conditions co-exist. Other authorities reckon that Alzheimer's disease is a factor in up to 80 per cent of cases of dementia. Parkinson's disease accounts for at least eight per cent of cases of dementia, brain injury for another four or five and an equal number are the result of other less common neurological conditions.

Alzheimer's is divided up into early disease and mild, moderate and severe. Other authorities like to describe seven stages ranging from possible dementia through very mild, mild, moderate, moderately severe, severe and very severe.

Alzheimer's disease is thought to have a genetic factor in around 20 per cent of cases, the familial link is found more often in cases in which the symptoms have appeared early in life. Even patients who have inherited the gene may not ever show signs of Alzheimer's disease and the potential effects of it remain, as doctors say, unexpressed. In others it might have been that they would have shown signs and symptoms but had died before they became apparent.

In the 80 per cent of patients of which there is no obvious familial link it is thought that environmental factors may be important. High blood pressure, and any other condition that might affect the blood supply to the brain, seems to be a factor in causing some cases of Alzheimer's disease as well as vascular dementia. Brain damage from whatever cause may also be a significant factor. The high incidence of Lewy body dementia in Parkinson's disease is now being understood.

Doctors usually tell patients that when a first degree relative has developed senile dementia - your father doesn't seem to have been given a more precise diagnosis - in old age there may be a slightly increased risk of developing it but this is very much less of a hazard than having the first degree relative who developed early Alzheimer's. The underlying problems associated with vascular dementia such as high blood pressure and atherosclerosis of the arteries, the furring up of the arteries, also has a familial pattern. Differentiating between normal forgetfulness, questionable dementia and very mild dementia is exceptionally difficult.

There are set questions and tests but drawing conclusions from them is difficult. In the early signs of Alzheimer's as well as memory loss and a shortened attention span there are several other symptoms to look out for. Has the patient difficulties in acquiring new knowledge and new techniques? Do they even find it difficult to perform well rehearsed simple tasks? Can they remember names for people and places? Are they ever searching not only for their keys, cheque book, spectacles, passport and pen but also for the correct word to describe something that is always "just on the tip of their tongue". More importantly are they finding it difficult to plan and do they become agitated by having to organise the simplest expedition? Are they unusually depressed or apathetic. There are very few people who are in their late fifties who don't have some of these symptoms and although there are 800,000 people with diagnosed dementia in the UK there are a great many more that have nothing wrong with them other than the benign dementia of old age.

Can you prevent Alzheimer's and other dementias? To keep intellectually, socially and physically active are important preventative measures as is a healthy diet. Blood pressure should of course be rigidly controlled and so should levels of cholesterol. Over the years there have been repeated suggestions that statins used to reduce cholesterol levels may also help reduce the incidence of dementia, presumably by helping to maintain an efficient cardiovascular system. One interesting piece of research done recently by the Alzheimer's Research Trust has shown that there is a relationship between a low IQ in childhood and vascular dementia in later life.

In my opinion the clue to lessening the effects of Alzheimer's and other dementias will be early diagnosis and early treatment. Both the Alzheimer's Research Trust and the Alzheimer's Society are doing sterling work into the research into methods that will detect early dementia and new forms of treatment when it is diagnosed. The tragedy, in fact it's a disgrace, is that when early diagnosis of Alzheimer's is made there is difficulty in persuading the National Health Service to pay for what treatment there is available to help it. It is a golden rule in medicine that early treatment, or the prevention of a condition so that it never becomes established, is of fundamental importance.

Q2: My sister, 78 has had declining memory and increasing confusion for three years and earlier this year was diagnosed with Alzheimer's. She is now on Aricept which seems to be helping to some degree but some days she is better than others. She also lives on her own so there is no way of knowing if she takes the medication regularly. Is there a pattern and time frame for further deterioration for people on Aricept? Name and address withheld