Alzheimer's causes unique cell death.

A new study documents the striking differences in brain cell loss experienced by the mentally alert elderly and those with Alzheimer's disease, researchers report.

The number of neurons, or brain cells, normally declines in old age. In Alzheimer's patients, however, that drop takes on a distinct pattern, Mark J. West of the University of Aarhus in Denmark and his colleagues report in the Sept. 17 LANCET. Cell death either leads to memory loss or results from the same process that causes memory deficits, scientists suspect.

The new study provides a quantitative assessment of the areas of the brain hardest hit by Alzheimer's, says Warren J. Strittmatter of Duke University Medical Center in Durham, N.C. The findings also offer additional evidence that Alzheimer's is not accelerated aging, as some researchers argue, but a unique pathological process, Strittmatter and the authors note.

The researchers determined the density of neurons in different parts of the hippocampus, a region of the brain that handles memory and shows early damage from Alzheimer's, the team reports. Unlike other researchers, they also calculated the volume of the areas of the brain they examined, says coauthor Dorothy G. Flood of the University of Rochester (N.Y.) Medical Center. Brain volume often shrinks in Alzheimer's patients, and that would affect neuronal density, she notes.

The team used tissue samples from 7 deceased Alzheimer's victims and from 38 people, age 13 to 101, who died with no history of long-term illness, dementia, or neurological disease.

"We noticed [Alzheimer's-]related neuronal loss in two subdivisions that normally lose neurons with age, the hilus and the subiculum, but also noticed neuronal loss in CA1, a region in which there is no evidence of normal age-related loss," they report. The Alzheimer's group averaged 68 percent fewer neurons in the CA1 than nondemented people of similar age.

The demented group lost more cells in the CA1 than in any other area of the brain examined by the team. Two of the Alzheimer's tissue samples had essentially no neurons, they note. The authors acknowledge, however, that they cannot rule out the unlikely possibility that the Alzheimer's patients had fewer neurons from an early age.

Alzheimer's disease results in physical changes in the brain in addition to cell loss. And it leads to gradual declines in cognitive abilities and to personality changes. Researchers have had a host of theories on the cause of this debilitating illness (SN: 1/1/94, p.8). Recently, investigators showed that inheriting one form of a molecule called apolipoprotein E increases a person's risk of developing Alzheimer's (SN: 5/7/94, p.295).