| VOL. 23, NO. 16||FEBRUARY 27, 1998 |
Genetic Test for Alzheimers May Improve Diagnoses
BY CAROLYN CONWAY
n the largest cooperative investigation to date among 26 federally-funded Alzheimers Disease Centers (ADCs) nationwide, researchers from Columbias College of Physicians & Surgeons, in collaboration with the National Institute on Aging (NIA), have discovered that the ApoE genetic test for Alzheimers coupled with a thorough clinical evaluation may help to confirm the diagnosis.
The study, in the Feb. 18 issue of The New England Journal of Medicine, emphasizes that results from the ApoE-4 genetic testwhich detects the presence of the apolipoprotein E (ApoE) gene in the DNA of a patients bloodby itself is inconclusive and does not provide sufficient evidence to diagnose Alzheimers disease.
Researchers discovered that when the ApoE test is administered, along with a thorough examination, the validation of the clinical diagnosis of Alzheimers disease could be greatly improved.
In 1995, the first commercial tests for Alzheimers disease risk prompted public health experts to call for more research and special legal protection for individuals genetic information. At that time the scientific community reached no consensus on the meaning of a positive test.
The United States spends more than $100 billion a year caring for people with Alzheimers disease.
The apolipoprotein E genotype may be undeniable as a genetic risk factor for Alzheimers disease, but its use as a diagnostic aid has received little attention until now, says Richard Mayeux, senior author and Gertrude H. Sergievsky Professor of Neurology, Psychiatry and Public Health (epidemiology) at Columbia-Presbyterian Medical Center. This study for the first time provides clarification of the usefulness of ApoE testing to help with diagnosis and treatment of Alzheimers.
We can not underestimate the usefulness of increasing a physicians (over) confidence in diagnosing a disease of this magnitude, says Creighton Phelps of the National Institutes of Health. When facing a family who must bear the weight of such devastating news, a majority of doctors would appreciate as many tools as possible to help them in their certainty of diagnosis and based on this research, ApoE testing may be one such tool.
Investigators, led by Mayeux, reviewed the eligibility of men and women referred to ADCs for diagnosis of dementia. The study examined records of 1,108 women and 1,080 men. Each patient examined had a battery of clinical and behavioral tests, followed by numerous laboratory and brain imaging studies. The patients were followed throughout the course of their disease and their brains were examined upon death.
Based on brain autopsies Mayeux found that 93 percent of the patients who were found to have Alzheimers, i.e, their brains showed clear evidence of Alzheimers-related changes, had been diagnosed by a physician as having the disease.
However, 45 percent of those found to have other forms of dementia at the time of brain autopsy had also been diagnosed by physicians as having Alzheimers. This high rate of false positive diagnoses (45 percent) show the limitations of using recommended clinical criteria alone.
Mayeux and colleagues examined the effect of the ApoE genotype in reducing false positive diagnoses and in adding to the assurance of clinical diagnoses. By using the ApoE genotype only in patients who first met clinical criteria for Alzheimers, the false positive rate of diagnosis decreased from 45 percent to 16 percent.
Other Columbia authors were Steven Shea and Ming-xin Tang.