Some Alzheimer’s Disease May Be Linked to Virus

A virus may cause at least some cases of Alzheimer’s disease, a mental disorder that affects about 2.5 million Americans, according to researchers at Yale University.

The researchers found that white blood cells from relatives of Alzheimer’s victims caused an Alzheimer’s-like disease when they were injected into hamsters.

Neurologists have long suspected that Alzheimer’s might be caused by a virus, but more than 50 previous attempts to transmit the disease to animals were unsuccessful. Researchers have thus been somewhat skeptical of the new findings, published this week in the Proceedings of the National Academy of Sciences.

Caution Urged

“One has to be extremely cautious . . . because this is an extremely preliminary pilot study,” said neurologist David Drachman of the University of Massachusetts Medical School. “I am certainly not ready yet to conclude that Alzheimer’s disease is, in any sense, infectious or transmissible,” said Drachman, who is chairman of Alzheimer’s Disease and Related Disorders Assn.’s Medical and Scientific Advisory Board.

But the paper is important because “it is essentially reopening an approach that has been closed for a long while because of negative findings--the search for a potentially infectious” cause, said neuroscientist Andrew Monjan of the National Institute on Aging in Bethesda, Md. “Now what is necessary is further study to try to repeat the results.”

Alzheimer’s is characterized by the massive destruction of brain cells, which leads to loss of memory, loss of the ability to care for oneself and, eventually, to death. About 120,000 people die from it each year in the United States. Its cause is not known and there is no effective treatment.

Researchers hope that implication of a virus as a cause of Alzheimer’s will lead to new ways to treat or even to prevent the disease.

Cells From Autopsies

In the past, researchers have attempted to find an Alzheimer’s virus by injecting animals with brain cells obtained during autopsies of Alzheimer’s victims.

But Yale virologist Elias E. Manuelidis and neuropathologist Laura Manuelidis reasoned that the virus may no longer be present in the brains of victims with full-blown disease--as is the case, for example, with polio. The virus is more likely to be present, they reasoned, at earlier stages of the disease or even before symptoms become apparent.

Reasoning that family members would be at highest risk of being infected, the husband-wife team obtained blood specimens from 11 individuals who had at least two siblings or parents with Alzheimer’s. Nine of the volunteers were completely healthy and two had early signs of the disease. The latter two volunteers subsequently developed Alzheimer’s and one died from it, but the other nine have remained healthy.

The researchers injected white blood cells from the samples into the brains of hamsters. The hamsters that received white cells from five of the volunteers--including the two with Alzheimer’s--developed neurological changes in their brains similar to those caused by a rare Alzheimer’s-like disease called Creutzfeldt-Jakob disease, which is known to be caused by a virus. Animals who received cells from the other six people developed no such symptoms, suggesting that perhaps those six were not infected.

Further Injections

Brain tissue from three of the hamsters that developed the symptoms was ground up and injected into other hamsters. Those hamsters also developed the symptoms.

White blood cells from four “control” individuals with no family history of Alzheimer’s did not produce any symptoms when injected into hamsters, Manuelidis said. But she conceded that four was a very small number of controls. “We would like to see a lot more samples,” she added.

The team is planning to work with the National Institute on Aging to study a much larger number of both Alzheimer’s relatives and healthy individuals, but she noted that such studies are time-consuming and expensive. The average time between inoculation of the hamsters and appearance of the disease was 352 days, she said, and one case required 517 days.

They are also monitoring the health of the donors to see if any more develop Alzheimer’s. “It may be that you can have an infection by the virus without ever developing the disease--just as is the case with the polio virus,” she said. The Creutzfeldt-Jakob virus, or one like it, may cause Alzheimer’s in the presence of a genetic susceptibility or some environmental factor.

Meanwhile, both Manuelidis and Monjan downplayed the risk to family members of Alzheimer’s victims.