Living with Dementia May 2008

Lead researcher of the Seattle-based team Dr Suman Jayadev says,

We decided to assess the strength of genetic risk factors because enough people came to us asking, "Both my parents have Alzheimer's disease, so what's my risk?"

The 111 couples studied had 297 children who survived to adulthood. Of these, 22.6 per cent developed Alzheimer's disease compared to a rate of between six and 13 per cent in the general population. According to Dr Jayadev,

The implication is that we all have risk factors for Alzheimer's which are probably very small individually. But if you carry multiple small changes you increase your risk to a discernible difference.

The team will continue to monitor the group as the offspring get older, as some of the group have yet to reach 70.

So what is a risk factor?

A genetic risk factor is an inherited susceptibility or tendency towards developing a condition, rather than a guarantee that a condition will develop. Other factors, such as decisions about how we live our lives, will interact with this susceptibility in determining our future health. 

It is possible that someone who has inherited a genetic risk factor for Alzheimer's disease can avoid triggering it. For example, we know that being overweight or having high blood pressure increase chances of developing Alzheimer's disease. But if someone with a certain genetic risk factor exercises regularly and maintains a healthy blood pressure, the inherited weakness might not be exposed and the disease may not develop.

Genetic risk factors can be likened to slightly faulty parts in a machine: if they are not put under too much pressure, the faulty parts may not change and the person will stay healthy.

Identifying the genes

Pinning down exactly which genes are behind these risk factors will provide an important new framework for understanding Alzheimer's disease. In the UK, Professor Julie Williams at Cardiff University is co-ordinating the largest study of the genetics of Alzheimer's disease in the world.

She says,

We could spend the next 100 years researching which theories about the cause of this disease are correct, but finding the genes which are involved points us in the right direction now.

Professor Williams' team will analyse the genes from 6,000 people with Alzheimer's disease and contrast them with 10,000 control subjects who do not have the disease. Technological developments are making important differences to the possibilities of research in this area.

As Professor Williams explains,

We now have tiny chips which literally have a million mini-experiments on them. We can analyse the genes of a person for just £200, when a couple of years ago this would have cost hundreds of thousands of pounds. There is now great optimism amongst geneticists that we are going to pin down the genes that make people susceptible to Alzheimer's disease. We are on the verge of establishing very important new information about the genetic risk factors for this condition.

Professor Williams' team expect to have the first wave of their results by the end of the year.

Commenting on the role of genetics and dementia, the Society's Head of Research Dr Susanne Sorensen said,

The role of genetics in the development of dementia is still not fully understood. It is clear that genes do play a role but the largest risk factor remains your age. As one in three people who live to over 65 will die with dementia it is vital that more research is carried out to fight this devastating condition.