Two tests

The study, conducted by Andy Ellis of the University of York and his collaborators at the Universities of Hull and Aberdeen, characterised shrinking vocabulary in the early stages of the disease.

The researchers asked 96 Alzheimer's patients and 40 healthy people of similar age to list all the animals they could in one minute. In a second minute, the test subjects were asked to list types of fruit.

While the healthy subjects were able to list 20-25 words, on average, those suffering from Alzheimer's could list only 10-15, indicating a constriction of their active vocabulary.

The lost words tended to be those learned later in childhood and encountered less frequently in everyday life.

Clear distinction

Common words like "dog" and "cat" were generally learned before the age of five, said Professor Ellis, and were listed by both groups.

In contrast, "giraffe" and "zebra", usually learned later in life and less frequently used, were seen to drop out of the vocabulary of the Alzheimer's sufferers.

The pattern of vocabulary loss was so consistent that it was possible for researchers to correctly identify the healthy and ill test subjects on the basis of their word lists alone.

It is this, says Professor Ellis, which may allow development of improved diagnostic screening for Alzheimer's.

Early intervention

"What we're going to try to explore is the possibility that a very simple task - generating words from categories - might alert GPs to the fact that something is beginning to go wrong," he told the British Association's Festival of Science, which is being held this year in Ireland.

The word task involves a slightly different part of the brain than those probed by currently used memory tests, according to Professor Ellis, and so may provide an alternative, possibly earlier, indication of the illness.

"It may be that the reason why this test is sensitive to the condition is because it requires the functioning of areas of the brain which are affected early in the development of Alzheimer's disease," he explained.

Because the drugs which are beneficial in treating Alzheimer's work best when they are administered early in the illness, there may be considerable benefit in the new test.

Future screening

The word task may also be valuable because its interpretation could be tuned to account for natural variation in vocabulary among people.

"People with a high vocabulary will often detect that they are having problems," explained Professor Ellis, "but if you give them a standardised test they perform above average."

The novelist Iris Murdoch was able to complete her last novel while in the early stages of Alzheimer's, but a vocabulary analysis of the book published in the journal Brain last year revealed a loss of more obscure words similar to that identified by Professor Ellis and his colleagues.

If it is possible to generate simple and reliable cognitive tests, says Professor Ellis, annual screening for Alzheimer's may become desirable as the population ages. According to a UN study, nearly 35% of the population of developed countries will be over 60 by 2050.