A gene associated with Alzheimer’s disease may impact the brain, particularly cognitive health, even before adulthood, a new study found.
A team of researchers at the University of California, Riverside, has found that cognitive health decline starts earlier in people who have Alzheimer’s disease.
The Apolipoprotein E (APOE) is a major cholesterol carrier that aids in lipid transport and injury repair in the brain. It packages cholesterol and other fats and moves them through the bloodstream. APOE polymorphic alleles are the major genetic factors for the risk of Alzheimer’s disease (AD).
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APOE4 gene linked to Alzheimer’s disease
There are three major types of APOE, the APOE4 allele exists in about 15 percent of the population. In fact, people who carry the APOE4 allele are three times more likely to develop Alzheimer’s disease (AD) compared to those who carry the more common APOE3 allele. On the other hand, APOE2 allele reduces the risk of AD.
The previous body of knowledge has shown that the gene is associated with changes in cognitive aptitude, which are most obvious as early as a person reaches his 50s.
APOE carriers scored lower on IQ tests
But the new study published in the journal Neurobiology of Aging, the researchers said that people who are carriers of the APOE4 gene had lower IQ scores during childhood and adolescence. Plus, the impact on girls was stronger than boys.
“Our results suggest that cognitive differences associated with APOE may emerge early and become magnified later in the life course, and if so, childhood represents a key period of intervention to invest in and boost reserves. APOE effects on cognition from childhood to adolescence,” the researchers said in the study.
To land to their findings, the researchers analyzed data from the Longitudinal Twin Study and the Colorado Adoption Project, which are three to four decades old. These studies involved genotyping data from 1,321 participants when they were about 6.5 years old to 18 years old. During the duration of the study, there were three IQ tests between childhood and adolescence.
They found that those individuals who carry the APOE4 allele scored lower on IQ tests by 1.91 points. Also, the researchers said that a person can carry up to two APOE4 alleles. The more alleles a person has, the greater the impact on his or her IQ performance.
According to gender, males scored 0.33 points lower on IQ tests while girl respondents scored nearly 3 points lower for each APOE4 allele. The findings also show that reasoning was the trait most affected by the gene.
According to the researchers, though the IQ score difference is small, it can affect a person’s cognitive ability in the long run. The APOE4 carrier ages, and as years pass by, the gene’s impact my progress.
What is cognitive reserve?
Cognitive reserve means the brain’s ability to solve problems and troubleshoot solutions. The cognitive reserve theory says that people with a reduced cognitive reserve may have more problem tolerating disease as they grow old.
Some studies have also shown the link between lower childhood IQ and magnified biological aging, such as cell and tissue injury or damage, and cardiovascular disease even before they reach 65 years old.
Alzheimer’s disease and cognitive health
Alzheimer’s disease is a neurodegenerative disease that affects a person’s cognitive abilities. First, it affects memory and thinking skills, but as the disease progresses, it can affect a person’s ability to carry out simple tasks. In most people with Alzheimer’s disease, the symptoms first appear in their mid-60s, but in some cases, the disease may manifest earlier.
Worldwide, an estimated 44 million people are living with Alzheimer’s disease or a related type of dementia. In the United States, approximately 5.5 million have Alzheimer’s disease, making it the 6th leading cause of death in the country.
There is still no exact cause of Alzheimer’s disease, but many experts say age is the best-known risk factor of AD. However, people with a family history of AD are at a higher risk of developing the disease. Also, the presence of certain genes may also increase one’s risk.
Some studies have also shown that brain changes may occur years before the first symptoms appear. In some studies, however, diet, environmental factors, and education may also play a pivotal role in developing AD.
Carol E. Franz, Hong Xian, Daphne Lew, Sean N. Hatton, Olivia Puckett, Nathan Whitsel, Asad Beck, Anders M. Dale, Bin Fang, Christine Fennema-Notestine, Richard L. Hauger, Kristen C. Jacobson, Michael J. Lyons, Chandra A. Reynolds, William S. Kremen, Body mass trajectories and cortical thickness in middle-aged men: a 42-year longitudinal study starting in young adulthood, Neurobiology of Aging, https://doi.org/10.1016/j.neurobiolaging.2019.03.003, http://www.sciencedirect.com/science/article/pii/S0197458019300818