TORONTO - Cognitive testing can predict with 90% accuracy which patients with memory problems will go on to develop Alzheimer's disease (AD), researchers here report.
This high score with two cognitive tests compared favorably with genetic screening for the e4 allele of the apolipoprotein E gene, which was only 74% accurate in predicting who would go on to develop AD, said Dr. Mary Tierney (PhD), a research scientist at Sunnybrook Health Science Centre.
Dr. Tierney, in collaboration with Dr. Peter St. George-Hyslop of the University of Toronto, reported the findings in two papers in the January issue of Neurology.
Their hope in undertaking this project, she said in an interview, was to help physicians who are faced with a patient with mild memory loss.
"Right now, it's really difficult for family doctors to know if they should put the patient through extensive testing or tell the family to start filling out forms for the nursing home," she said.
"We're attempting to identify those at risk so they may be able to get into the drug trials, and also to reassure those who aren't going to progress quickly."
In this study, 123 patients referred to Sunnybrook by GPs were given a series of cognitive tests and genetic testing, and then followed for two years.
They were then put through a thorough diagnostic assessment for the presence of AD. Of the 123 patients, 29 developed the disease and 94 remained stable, "which in itself is a positive finding."
They then looked at which of the baseline tests were most predictive of progression to AD. A combination of two of the cognitive tests had the best results at an 89% accuracy.
These were a delayed recall test, in which the person was taught new information and after a time delay, asked to recall it. The other was a measure of attention and concentration, performing relatively simple mental tasks as quickly as possible.
"So these two skills ... seem to be very important in predicting who later develops Alzheimer's disease."
Adding genetic testing did not appear to increase the accuracy achieved by the cognitive tests.
"This is not just an academic question," she said. "There are drug trials out right now, the pharmaceutical companies are actively trying to develop something to arrest the progression of Alzheimer's disease.
"If drugs are ever developed, you're going to want to get people as early as possible, because if you can get them before they show symptoms, you can really improve the quality of their life.
The majority of subjects did not progress, and family doctors could offer them some assurance of remaining stable at least for the next two years, she added.
Most importantly, the combination of cognitive tests did not appear to falsely identify people who did not progress as being at risk. "The worst possible thing for a patient is to tell them they will develop Alzheimer's when they won't," Dr. Tierney said.
Copyright © 1996 Maclean Hunter Publishing Limited
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