The study is published in the March 1 issue of Neurology.
A small amount of brain shrinkage with each passing year is common among older adults and not necessarily a sign of Alzheimer's, Burns noted.
However, with Alzheimer's, the atrophy occurs much faster.
Researchers don't know what the Alzheimer's-related inheritance from mothers is, but they theorize that it may have something to do with mitochondrial dysfunction. Mitochondria, which generate the energy that cells use to function, are inherited only from mothers.
Prior research has linked mitochondrial problems and Alzheimer's disease, Burns said.
"This suggests that the mitochondrial dysfunction may have more to do with Alzheimer's than we previously have considered," he said.
Dr. Steven DeKosky, a professor of neurology at University of Virginia School of Medicine, said too few participants were involved in the study to draw a conclusion. Larger studies are needed to confirm the findings, he said. In addition, researchers did not test for specific proteins associated with Alzheimer's, such as those found in cerebrospinal fluid.
Testing for those protein markers could confirm if the atrophy was indeed due to Alzheimer's, DeKosky said.
"I would be very cautious about reaching any firm conclusions about genetics from this study," DeKosky said.
"They probably have identified AD [Alzheimer's disease] cases which are presymptomatic, but whether the male-female difference will be maintained would await larger numbers of cases, perhaps more thoroughly characterized," he added.
With Americans living longer, cases of Alzheimer's disease are soaring in the United States. By 2030, about 20 percent of the total U.S. population will likely have the disorder, the Alzheimer's Association estimates.
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