Neanderthal genes could be related to human risk for COVID-19

For every 100 of those infected with the coronavirus (which has now reached a global total surpassing 113 million confirmed cases), about 30 individuals are asymptomatic. Not only do they not present symptoms within the first two weeks of receiving the virus, but they go on to never display any signs of the virus. This makes them perfect carriers for the coronavirus.

This finding was presented in Thorax, a monthly peer-reviewed journal specializing in respiratory medicine, along with the observation that those asymptomatic carriers were 75 percent as likely to transmit the virus as symptomatic carriers. In other words, people who showed no symptoms were 75 percent as likely to transmit the coronavirus to others when compared to those who displayed symptoms.

So what’s the underlying factor responsible for whether one shows symptoms of the coronavirus when infected — is it lifestyle, age, gender, weight, heredity, or geographical location? The answer, surprisingly, might lie within two specific sections of Neanderthal DNA.

Neanderthals are one of the many ancestors of modern humans. They roamed the Earth for a long time before homo sapiens, the scientific name for humans, became the dominant species of the genus homo. The extinction of Neanderthals 40,000 years ago was attributed to various factors such as climate change or an unknown disease. However, much of their DNA remains prominent in the human genetic code. According to the Smithsonian, there is a 1 to 4 percent overlap between Neanderthals and modern humans today.

Interested in investigating this similarity between Neanderthal and human DNA, the researchers at the Karolinska Institute in Sweden collaborated with the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany to find a major genetic risk factor located on chromosome 3 of the human genome. This risk factor is directly linked to a dramatic increase in the risk of respiratory failure, and has also been linked to a higher risk of coronavirus mortality. A single copy of a particular version of chromosome 3 has been known to lead to cells being unable to rally immune defenses when faced with the virus.

This itself is not a new finding; there has been much prior research stating that chromosome 3 also plays an important role when a person is infected with a flu virus. Yet, scientists Hugo Zeberg (Karolinska Institute) and Svante Pää (Max Planck Institute for Evolutionary Anthropology) found that the version of chromosome 3 that increases a person’s risk for showing symptoms of the coronavirus is almost identical to the chromosome present in Neanderthals. Thus, the researchers suspected that inherited Neanderthal DNA was directly responsible for a person’s likelihood to be asymptomatic when infected with COVID-19.

Still, this is only half of the story. Almost two weeks ago, these same researchers also discovered another genetic factor present on chromosome 12. Unlike the genetic factor on chromosome 3, this newest one actually reduces the risk of needing intensive care upon infection with the coronavirus. This is due to oligoadenylate synthase (OAS) genes, which counters viral attacks that take place in the body. 2’-5’ oligoadenylate synthase (OAS1) is one such gene located on chromosome 12, and its main purpose is to regulate the activity of an enzyme that breaks down the virus’ genes.

Out of the variants of OAS1, the version directly inherited from Neanderthals was found to be the most effective at breaking down invading viruses’ genes.

To test the direct effects of OAS1, researchers at McGill University in Ontario, Canada conducted a two-sample randomization study among 504 individuals, all of whom were infected with the virus. The results of this study showed a high level of OAS1 was associated with a lower likelihood of contracting the virus, as well as reduced severity of coronavirus symptoms. The researchers currently have plans to use this finding to create pharmacological treatments to increase OAS1 levels in patients to improve immunity.

In addition to the fields of infectious medicine, this new finding relating Neanderthal genes with COVID-19 immunity is a great revelation for the fields of evolutionary biology, especially when it comes to solving the mystery behind the extinction of Neanderthals. Many scientists speculate that Neanderthals might have faced extinction due to a pandemic similar to the one that humanity is facing right now. Since the end of the Ice Age 11,500 years ago, the two genetic variants of Neanderthal DNA, especially the protective variant on chromosome 12, have greatly increased in frequency thanks to human migration. This could imply that humans have a greater, natural immunity to the coronavirus than their ancestors did. However, there is still much more left to understand about genetic interactions, as well as Neanderthal physiology, before anything can be concluded.