Some people may have genes inherited from Neanderthals that reduce their risk of severe COVID-19 by 22%, a study found.
But the same researchers previously found that Neanderthal DNA can also put people at higher risk of respiratory failure due to COVID-19.
The inherited genes are more common in Europe and Asia.
As an emergency room doctor, Hugo Zeberg has seen first-hand how widely COVID-19 infections can vary in severity. So he started digging for answers in a place that was familiar to him: the genome of Neanderthals.
Zeberg works at the Karolinska Institute in Sweden, and for the last couple of years, has been studying the degree to which Neanderthals - an extinct human species that died out about 40,000 years ago - passed along genes to modern humans through interbreeding.
Scientists think Neanderthal DNA makes up 1% to 2% of the genomes of many people of European and Asian descent. That small fraction of people's genetic codes may hold important clues about our immune responses to pathogens.
In a study published this week, Zeberg and his colleague Svante Pääbo at the Max Planck Institute for Evolutionary Anthropology suggest that some people may have inherited a genetic advantage that reduces their risk of getting severe COVID-19 by 22%.
The advantage comes from a single haplotype - or long block of DNA - on chromosome 12. The same haplotype has been shown to protect people against West Nile, hepatitis C, and SARS (another coronavirus that shares many genetic similarities with the new one, SARS-CoV-2).
"The protective effect of this haplotype is probably not unique to SARS-CoV-2, but a more general part of our immune system," Zeberg told Insider.
Some Neanderthal genes are helpful, others are harmful
Zeberg and Pääbo found that the Neanderthal-inherited haplotype may have become more common among humans in the last 1,000 years. One possible explanation for this, Zeberg said, is the genes' role in protecting people against other diseases caused by RNA viruses.
For their new study, the team relied on the genomes of three Neanderthals - two whose remains were found in southern Siberia and one from Croatia. The DNA dates back 50,000 to 120,000 years. They compared those Neanderthal genomes to the DNA of thousands of people with severe COVID-19.
The haplotype associated with less severe COVID-19 was found in all three Neanderthal genomes. It codes for proteins that activate enzymes that help degrade RNA viruses.
However, a prior study from Zeberg and Pääbo, published in September, showed that not all Neanderthal DNA confers an advantage. In that research, they found that some modern humans have inherited a haplotype on chromosome 3 that puts them at higher risk of respiratory failure due to COVID-19. That particular gene cluster was found in the Neanderthal from Croatia.
"If you have that variant, you have twice the risk of getting severely ill with COVID-19 - perhaps even more," Zeberg said.
Zeberg's research suggests that around 25% to 30% of people in Europe and Asia carry the protective haplotype, while up to 65% of people in South Asia and 16% of people in Europe carry the dangerous one. Unfortunately, he said, the protective haplotype doesn't offset the risk of the dangerous one for those who have both.
Lingering mysteries about how genes influence COVID-19
For the most part, people in Africa don't seem to have inherited any genes from Neanderthals.
"Neanderthals went to Europe and to Asia and lived there before modern humans," Zeberg said. "Then modern humans came 100,000 years ago and they probably mixed 60,000 years ago. So Africa has never met Neanderthals."
He added, though, that it's possible that Africans inherited a similar mutation from a different ancestor that could also confer protection against COVID-19.
"There are variants in Africa that we and others are looking into," Zeberg said.
Scientists still don't know how much of our protection against disease was inherited from ancient ancestors versus acquired more recently. Figuring that out is made more difficult by the fact that part of the Neanderthal genome is still missing.
But studying ancient genes could still help reveal more about how the body responds to the coronavirus. A December study, for instance, identified eight locations on human chromosomes where particular gene variants were more common among critically ill COVID-19 patients.
"If we can get a deeper understanding of how our evolutionary history has shaped our immune system, that can be valuable," Zeberg said.
It's possible, for example, that human ancestors relied on specific genes to protect them from viruses that have since died out. That may explain why certain people's immune systems overreact to the new coronavirus, triggering inflammation that can prove fatal.
Zeberg said scientists have just started to scratch the surface of these findings.
Read the original article on Business Insider