Some cases of COVID-19 cause only mild symptoms, but some cause rapidly progressing respiratory failure and death.
Millions of people have died, and millions more have suffered. It’s unclear why some people develop mild or severe COVID-19 disease. A genetic study has determined some genes located on chromosome 3 are a major risk factor for severe COVID-19 infection and hospitalization.
It turns out that a region of chromosome 3 was inherited from Neanderthals and is found in the DNA of 50 percent of people of South Asian decent and 16 percent of Europeans.
Early in the pandemic, it became obvious there were risk factors that were predictors for the outcome of a COVID-19 infection. These include advanced age, obesity, male sex, as well as some other medical conditions. These risk factors don’t fully explain the range of different symptoms, so scientists looked for genetic factors that may play a role.
Previous studies identified six genes on chromosome 3 and a region of chromosome 9 that has the genes for the ABO blood type groups. Scientists discovered the variations in the genes in a particular region on chromosome 3 are most important in determining the severity of COVID-19.
The Stone Age lasted until about 5,000 years ago when humans started using metal instead of stone to make tools and weapons. Stone Age humans shared the planet with other hominins including Neanderthals and Denisovans, and some of their genes became part of human DNA as the result of interbreeding.
A Neanderthal DNA sample from Croatia had 11 of the 13 gene variants associated with a higher COVID risk. Three of the variants also are present in two other Neanderthal DNA samples from southern Siberia.
Neanderthals and modern humans split into two different species around 550,000 years ago, but populations of the two met and interbred when humans traveled out of Africa into Europe and Asia 50,000 years ago. It looks like these Neanderthal gene variants make some people more likely to suffer severe disease from SARS-CoV2.
We don’t know why, but the highest frequency of these Neanderthal variants is found in Bangladesh. Scientists in the United Kingdom have found people of Bangladeshi origin have twice the risk of dying from COVID-19 than the general population.
The DNA variations may have protected ancient populations from other diseases, and it just happened they make COVID infections worse. The risk variants are more commonly found in people from South Asia than East Asia, and Neanderthal DNA is almost never found in human genomes from Africa.
Now, the human population is suffering from the SARS-CoV2 pandemic and those with high risk gene variants are more likely to have severe disease or die, these gene variants may decrease in the population. We don’t know how the gene variants on chromosome 3 affect the progression of COVID-19, nor if they have an effect on infections by other coronaviruses or other pathogens.
When scientists figure this out, we may have new ways of treating this terrible disease.