The mutation was less common in the control groups in those cohorts, ranging in frequency from 0.12 percent to 0.19 percent. But the approximately threefold increase in frequency in Alzheimer's disease patients was preserved in pooled data from all four groups.
On the other hand, among the individual cohorts, the association was significant in only one, from Munich.
In an accompanying editorial, two other researchers commented that the study was important for its clear implication of inflammatory processes in at least a subset of Alzheimer's disease cases.
The findings "may generate new insights into the pathogenesis of late-onset Alzheimer's disease," wrote Dr. Harald Neumann of the University of Bonn in Germany and Dr. Mark J. Daly of Massachusetts General Hospital in Boston.
They also pointed out that the risk of Alzheimer's disease associated with the TREM2 variant was in the same range as for the much more common APOE epsilon 4 variant.
Severe loss of function in TREM2 from homozygous mutation is already a recognized human disorder known as Nasu-Hakola disease, Neumann and Daly added. In this condition, a number of organ systems are affected, with severe dementia a late-stage symptom. Most patients die by age 50.
Previous research has indicated that heterozygous carriers of the Nasu-Hakola mutation are at increased risk for late-onset Alzheimer's disease.