Treatment with donepezil led to an improvement in communication, language ability and mood stability in four people with Down's syndrome who tried out the drug.

Richard Hannaford reports: "They are calling for more research"

It is usually assumed that the disabilities associated with Down's syndrome are untreatable.

Researchers from Duke University Medical School, North Carolina, USA, noted beneficial effects on the four patients - aged 24-67 - within three months of taking donepezil.

The average time that each patient took donepezil was nine months. None of the patients experienced serious side effects.

The researchers, writing in The Lancet medical journal, do not claim their small study should lead to widespread use of donepezil.

But they say a larger study should be carried out to test the effects of the drug.

Genetic disorder

Dr Tony Holland urged caution about new drug

Down's syndrome is a genetic disorder.

Its effects, particularly in older patients, are similar to those seen in people with dementia due to Alzheimer's disease.

They include poor communication, short attention span, and changeable mood.

Donepezil, developed to combat Alzheimer's disease, alters the way brain cells communicate with each other.

However, Dr Tony Holland, of the Down's Syndrome Association, urged caution over hopes that donepezil could be a treatment for Down's syndrome.

He said people with Down's syndrome were at risk of developing Alzheimer's disease.

He said: "People with Down's syndrome may be helped by this medication that was developed for treating Alzheimer's disease.