问答题

Passage 2

Knowledge can be power. There is now a test to predict Alzheimer‘s disease two or three years before symptoms occur. The assessment, the first to give such early warning, identifies 10 molecules in the blood associated with the disease before symptoms start. The hope is that it might be able to predict Alzheimer‘s disease decades in advance and help the development of preventative therapies.

Globally, 35 million people are living with Alzheimer‘s. It is characterised by a toxic buildup of amyloid and tau proteins in the brain, which destroys the neurons. Several blood tests can diagnose the disease, but until now, none has had the sensitivity to predict its onset.

Howard Federoff at Georgetown University in Washington DC and his colleagues studied 525 people aged 70 and over for five years. The group showed no signs of mental impairment at the start of the study. Each year, the team performed a detailed cognitive examination and took blood samples from all the participants. During this time, 28 people developed Alzheimer‘s or mild cognitive impairment, thought to be the earliest noticeable sign of dementia, including Alzheimer‘s disease.

Analysis of the blood revealed that those who went on to develop Alzheimer‘s had depleted levels of 10 metabolites-the products of chemical reactions in the body-compared with those who showed no sign of dementia. These molecules predicted who went on to get Alzheimer‘s within the next three years with up to 96 per cent accuracy.

The 10 metabolites are involved in supporting and maintaining the neurons. "We think the decrease in these chemicals reflects the breakdown of neural populations in the brain,"says team member Mark Mapstone at the University of Rochester Medical Center in New York.

If the test is verified in trials with larger groups, it should provide a cheap and quick way of revealing Alzheimer‘s a few years in advance. Mapstone says that it may even be able to predict the disease much earlier, because the brain changes associated with Alzheimer‘s begin many years before symptoms occur. "These metabolic changes might occur 10 or 20 years earlier-that would give us a real head start on predicting the disease," he says.

The team is hoping to investigate this by looking back at other dementia studies in which blood has been taken over decades and seeing whether the chemical changes can be detected that early.

The group also analysed the full genome sequence of all of the participants in the study. That work has yet to be published, but Federoff says the changes in genes over the five years of the study are even more powerful than the metabolites at predicting who will develop dementia.

But with no treatments available, would anyone want to take these tests "In my experience, the majority of people are very interested to know whether they will get Alzheimer‘s," says Mapstone. "Knowledge is power. We may not have any therapy yet but we can get our financial and legal affairs in order, plan for future care and inform family."

If the test could predict the disease 20 years before symptoms appear, the implications are huge, he says. "Imagine what you would do in your early 40s to slow the onset of the disease. You could eat the right foods, avoid head trauma or do more exercise."

"In the short term, I think some people would want to know and some wouldn‘t," says Tracy Young-Pearse, a neurologist at Harvard Medical School. However, if treatments are developed that are only effective before neurons start dying in large numbers, then the choice will be easy, she says.

What are the implications of the test that can predict Alzheimer‘s 20 years in advance