London, Feb 22 An international team of researchers has found that a Covid-19 risk variant inherited from Neanderthals can reduce a person's risk of contracting HIV by 27 per cent.
Some people become seriously ill when infected with SARS-CoV-2 while others have only mild symptoms or no symptoms at all.
Our genetic heritage may contribute to individual Covid-19 severity risk.
The study led by a team from Karolinska Institutet in Sweden and Max Planck Institute in Germany showed that modern humans have inherited a major genetic risk factor for severe Covid-19 from Neanderthals.
The team studied this variant in ancient human DNA and observed that its frequency has increased significantly since the last ice age.
In fact, it has become unexpectedly common for a genetic variant inherited from Neandertals. Hence, it may have had a favourable impact on its carriers in the past.
"This major genetic risk factor for Covid-19A is so common that I started wondering whether it might actually be good for something, such as providing protection against another infectious disease," Hugo Zeberg, from Karolinska.
The study published in the journal Proceedings of the National Academy of Sciences revealed that the genetic risk factor is located in a region on chromosome 3 that consists of many genes.
There are several genes in its vicinity that encode receptors in the immune system. One of these receptors - CCR5 - is used by the HIV virus to infect white blood cells.
Zeberg found that people who carried the risk factor for Covid-19 had fewer CCR5 receptors. This led him to test whether they also had a lower risk of becoming infected with HIV.
"This shows how a genetic variant can be both good and bad news: Bad news if a person contracts Covid-19, good news because it offers protection against getting infected with HIV," Zeberg explained.
However, since HIV only arose during the 20th century, protection against this infectious disease cannot explain why the genetic risk variant for Covid-19 became so common among humans as early as 10,000 years ago.
"Now we know that this risk variant for Covid-19 provides protection against HIV. But it was probably protection against yet another disease that increased its frequency after the last ice age," Zeberg said.
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