Lingering Neanderthal DNA May Influence Depression

Neanderthal DNA from interbreeding may affect a range of traits, including depression. Michael Smeltzer, Vanderbilt University

Many of us have a little bit of Neanderthal running through our veins. But is this archaic DNA influencing our biology? According to new research, this genetic legacy may impart subtle but significant effects on a range of aspects of our physiology, from the brain to our blood, and may even influence our risk for depression and heart attack.

This fascinating new study, published in the journal Science, showcases how, even after tens of thousands of years, ancient interactions between our modern human ancestors and Neanderthals continue to impact us today. Roughly 60,000 years ago, as humans made their way out of Africa and into Asia and Europe, interbreeding with Neanderthals left modern-day people of Eurasian descent with as much as 4 percent Neanderthal DNA.

“Our work supports some previous hypotheses that this Neanderthal DNA, present in modern humans today, impacts traits related to the immune system and skin,” first author Corinne Simonti told IFLScience. “But we also discovered links with neurological and psychiatric phenotypes that really weren’t expected. Being able to see both in one study is very cool.”

To kick-start their work, the researchers from Vanderbilt University took advantage of a vast database called eMERGE, which helpfully links up medical records and information on a range of traits with genome data for thousands of individuals. From this, they analyzed almost 28,500 adults of European ancestry and compared their genes with previously sequenced Neanderthal DNA. This allowed them to pick up this ancient genetic material in modern samples and look for associations with particular phenotypes, or characteristics.

The researchers looked for Neanderthal genetic variants in modern populations. Gio.tto/Shutterstock

Backing up previous work, the researchers found that certain Neanderthal genetic variants were linked with a skin condition called actinic keratosis, whereby scaly patches of skin develop as a result of damage from the Sun’s UV rays. These arise as skin cells called keratinocytes start dividing abnormally, and the research suggests that some of our inherited Neanderthal genes may be involved in their differentiation. This is interesting, because keratinocytes help protect the skin from the damage by pathogens and the Sun. So it’s possible that acquiring these genes, which helped Neanderthals adapt to their environment, may have bestowed our ancestors an initial advantage as they migrated into new areas. But now that these traits are no longer needed in Western environments, they may actually end up causing problems.

This is backed up by the find that a Neanderthal gene was linked with increased blood clotting, or hypercoagulation. This may have helped our ancestors fend off novel pathogens in their new environment by quickly closing up wounds, but this phenotype is now detrimental because it can raise the risk of stroke.

Perhaps the most interesting and unexpected find was that multiple Neanderthal genes were associated with depression and a range of other psychiatric characteristics. While this doesn’t mean Neanderthals were depressed, this could again have links with skin phenotypes.

“There has been a connection between sunlight exposure and depression risk,” said Simonti. “It might be the case that if you’re better able to use UV radiation in a certain pathway, like making vitamin D, then this could help or harm you.”

While we’ve learnt a lot from the study, the researchers acknowledge its limitations due to being restricted to clinical phenotypes. But perhaps this will usher in a new wave of work where we look for lingering effects on other characteristics of modern-day humans. 

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