Washington ? Scientists appear to have found a fingerprint of Alzheimer’s disease lurking in patients’ spinal fluid, a step toward a long-awaited test for the memory-robbing disease that today can be diagnosed definitively only at autopsy.

Researchers at New York’s Weill Cornell Medical College discovered a pattern of 23 proteins floating in spinal fluid that, in very preliminary testing, seems to identify Alzheimer’s – not perfectly, but with pretty good accuracy.

Far more research is needed before doctors could try spinal-tap tests in people worried they have Alzheimer’s, specialists caution. But the scientists already are preparing for larger studies to see whether this potential “biomarker” of Alzheimer’s, reported today in the journal Annals of Neurology, holds up.

“We’re looking to an era in which the kinds of uncertainties that many patients and their families face about the diagnosis of Alzheimer’s disease will no longer be a problem,” predicts Dr. Norman Relkin, a neurologist and the study’s senior researcher.

About 4.5 million Americans have Alzheimer’s, a toll expected to more than triple by 2050 as the population grays. The creeping brain disease gradually robs sufferers of their memories and ability to care for themselves, eventually killing them. There is no known cure; today’s drugs only temporarily alleviate symptoms.

Currently, doctors diagnose Alzheimer’s mainly by symptoms. That makes early diagnosis particularly difficult, and even more advanced disease can be confused with other forms of dementia. Nor is there a good way to track the disease’s progression, important both for decisions about patient care as well as in testing the effectiveness of new drugs.

Major research is under way to try to change that, including a $60 million study to give brain scans to 800 older Americans and try to pin down the earliest brain changes associated with Alzheimer’s.

At the same time, scientists also are hunting what they call biomarkers – signs of the disease in areas other than hard-to-test brain tissue.

By hunting for one protein at a time, scientists have discovered a few biomarker candidates in cerebrospinal fluid. But Relkin and colleagues at Cornell University expanded the hunt: Using a technology called proteomics, they simultaneously examined 2,000 proteins found in the spinal fluid of 34 people who died with autopsy-proven Alzheimer’s, comparing it to the spinal fluid of 34 non-demented people.

What emerged were 23 proteins, many that by themselves had never been linked to Alzheimer’s but that together formed a fingerprint of the disease.

Then the researchers looked for that protein pattern in the spinal fluid of 28 more people – some with symptoms of Alzheimer’s or other dementia, some healthy. The test indicated Alzheimer’s in nine of the 10 patients that doctors suspect have it, and incorrectly fingered three people.