Researchers have long known about the APOE gene. It tells cells how to make a protein called apolipoprotein E. The protein combines with fats called lipids in the body to make molecules called lipoproteins.
Alzheimer’s gene may show effects on brain starting in childhood, study suggests. July 14, 2016
The APOE gene has three variations, with e2, e3, and e4 being the most common. We all carry two copies of the APOE gene, one inherited from each parent. Researchers say that the most common variant is e3, with at least one copy being carried by about 50 percent of the population.
The research, published in the journal Neuron May 18, 2016, explained that of the six possible combinations of the APOE gene, those who carry one, and especially two of the e4 variants are more likely to develop Alzheimer’s disease than people without the variant.
Interestingly, the e2 variant is carried by only about eight percent of the population, but the research showed that while there may be more plaque in their brains, these people were far less likely to have symptoms of dementia.
Dr. Linda Chang, a neurologist at the University of Hawaii, who led the study, says that because the e2 variant is so uncommon, little is actually known about its function, but there is evidence it is “neuroprotective,” and may lower the risk of dementia unless it is paired with the e4 variant.
The research involved around 1,200 adolescents, age three to 20 from around the country who were enrolled in the Pediatric Imaging, Neurocognition, and Genetics Study. Saliva samples were used to sequence their DNA. The participants were then given a series of tests to measure various aspects of cognitive function, and they got MRI scans so researchers could visualize their brains.
There were differences found in cognitive function and the size of the brain’s hippocampus, which tended to be smaller with the subjects carrying the e2/e4 combination. Overall, 62 percent of the subjects carried two copies of e3, while around 25 percent carried at least one copy of e4. Less than two percent had two copies of the e4 variant.
The findings do not mean everyone should rush out and have their children tested, says brain researcher Rebecca Knickmeyer. She suggests that while brain development at any given age is more dependent on an adolescent’s “trajectory’ in development, the results could mean that Alzheimer’s could be considered a developmental disorder.
But even with all the research, Knickmeyer points out that there are many patients with Alzheimer’s who don’t carry the e4 gene variant, while many more people with the e4 variant don’t have Alzheimer’s or never develop the disease.
