A team of researchers has found that a harmful genetic mutation is actually helpful in certain circumstances. People who still live traditional hunter-gatherer lifestyles can benefit from the apolipoprotein E allele, a mutation that is normally connected to cardiovascular disease and Alzheimer’s disease. The details are in a paper that was just published in The FASEB Journal.
The apolipoprotein E (E4) allele has generally been considered a harmful mutation. An allele is an alternate version of a gene and the E4 allele is connected to serious problems such as cardiovascular disease. The E4 allele also leads to rapid age-related cognitive decline and puts people at high risk of developing Alzheimer’s disease later in life. Interestingly, the allele is more common in tropical regions near the equator. These same regions also contain numerous parasites and many of them can cause cognitive decline. Researchers began to wonder if the E4 allele had a different purpose in certain human societies.
Scientists from Arizona State University studied a group of Amazonian forager-horticulturalists called the Tsimane. The Tsimane community lives a more traditional lifestyle without modern amenities. A lack of modern medicine combined with a tropical environment has left the population susceptible to parasites. The Tsimane people are vulnerable to pathogens and have high parasite burdens. About 70% of Tsimane women are infected with roundworms, for example. Since many of these parasites cause cognitive issues, the research team expected that the presence of the E4 allele would cause even faster cognitive decline. They partnered with researchers from the Tsimane Health and Life History Project to determine if the E4 allele puts the Tsimane at an even higher risk of cognitive decline.
The research team was surprised to find that Tsimane people with the E4 allele actually showed less cognitive decline, even with heavy parasite loads. The allele appeared to help protect against some of the parasites that normally cause cognitive problems. Although the E4 allele is considered a dangerous mutation in modern society, it seems to be useful in certain populations that are regularly exposed to parasites.
The team’s findings may change the way researchers think about certain “harmful” alleles. The E4 allele is considered the largest risk factor for developing Alzheimer’s disease yet was beneficial to Tsimane populations. The team suggests that many alleles that appear to be completely harmful most likely served a purpose in more traditional human societies.
Trumble et al. Apolipoprotein E4 is associated with improved cognitive function in Amazonian forager-horticulturalists with a high parasite burden. The FASEB Journal (2016).