Alzheimer's clues from thin brains.

Some kids on the cusp of adolescence display a genetically influenced brain trait that may raise their likelihood of developing Alzheimer's disease later in life. The entorhinal cortex, a neural area targeted by this devastating condition, is substantially thinner in youths who possess a gene variant previously linked to Alzheimer's disease than it is in their peers who inherit other versions of the same gene, say Philip Shaw of the National Institute of Mental Health in Bethesda, Md., and his coworkers.

Young people with the Alzheimer's-related variant of the apolipoprotein (ApoE) gene, which influences brain-cell repair, showed no IQ differences compared with those who had other variants of the gene, Shaw's group reports in the June Lancet Neurology.

However, such individuals maybe prone to mental declines as the entorhinal cortex shrinks with age, the scientists theorize.

Prior studies implicated one of three versions of the ApoE gene in Alzheimer's disease. The critical variant occurs in 40 percent of people who develop the brain disorder late in life. That's at least double the prevalence of that variant in the general population.

Shaw and his colleagues studied 239 children and teens, 65 of whom possessed the Alzheimer's-related Apo E variant. Magnetic-resonance imaging scans measured tissue thickness in each volunteer's entorhinal cortex. Most participants returned for one or more scans at roughly 2-year intervals.

A relatively thin entorhinal cortex represents a stable trait in people with the Alzheimer's-related ApoE variant, the researchers add. From one brain scan to the next, the entorhinal cortex didn't get thinner during the study.