A gene linked to Alzheimer’s Disease may impact cognitive health as early as childhood, according to a new study published in the journal Neurobiology of Aging. The effect appears to be more pronounced in girls.
The APOE gene produces a protein, called “apolipoprotein E,” which packages cholesterol and other fats to transport them through the bloodstream.
There are three versions, or alleles, of APOE, but the one of interest in this study is the APOE4 allele, present in about 15 percent of the population. People with this gene are up to three times more likely to develop late-onset Alzheimer’s disease.
Previous research has shown that the gene is linked to changes in cognitive ability as early as a person reaches his or her 50s. But the new study suggests that APOE4 starts manifesting much earlier — well before adulthood.
According to the study, those carrying the APOE4 gene score lower on IQ tests during childhood and adolescence. And the effect was stronger in girls than in boys.
Researchers from the University of California, Riverside (UCR) conducted an analysis of decades-old studies: the Colorado Adoption Project and the Longitudinal Twin Study.
The studies include genotyping data from 1,321 participants when they were 6 ½ to 18 years old. Gender among participants was split almost evenly, and 92 percent of the participants were white, with 8 percent from other races. The findings are based on three IQ assessments between childhood and adolescence.
Overall, full-scale IQ scores were lower by 1.91 points for each APOE4 allele; a person can have up to two APOE4 alleles. Males with the allele scored .33 points lower on IQ tests, and females scored almost 3 points lower for each allele. The traits most affected related to reasoning. The effect of the allele on IQ performance multiplies with each E4 allele present.
The IQ difference seems small. But long-term, it can mean fewer cognitive reserves as the APOE4 carrier ages, with the disadvantage becoming progressively magnified.
Cognitive reserve is the brain’s ability to navigate problems and improvise. Cognitive Reserve Theory holds that people with fewer reserves have more trouble withstanding disease as they age.
Studies have also shown a link between lower childhood IQ and increased biological aging — cell and tissue damage — and cardiovascular disease before age 65.
“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,” writes UCR professor Dr. Chandra Reynolds.