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severe COVID-19

Genes, Blood Type Tied to Risk of Severe COVID-19

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SARS-CoV-2 virus particles
Caption: Micrograph of SARS-CoV-2 virus particles isolated from a patient.
Credit: National Institute of Allergy and Infectious Diseases, NIH

Many people who contract COVID-19 have only a mild illness, or sometimes no symptoms at all. But others develop respiratory failure that requires oxygen support or even a ventilator to help them recover [1]. It’s clear that this happens more often in men than in women, as well as in people who are older or who have chronic health conditions. But why does respiratory failure also sometimes occur in people who are young and seemingly healthy?

A new study suggests that part of the answer to this question may be found in the genes that each one of us carries [2]. While more research is needed to pinpoint the precise underlying genes and mechanisms responsible, a recent genome-wide association (GWAS) study, just published in the New England Journal of Medicine, finds that gene variants in two regions of the human genome are associated with severe COVID-19 and correspondingly carry a greater risk of COVID-19-related death.

The two stretches of DNA implicated as harboring risks for severe COVID-19 are known to carry some intriguing genes, including one that determines blood type and others that play various roles in the immune system. In fact, the findings suggest that people with blood type A face a 50 percent greater risk of needing oxygen support or a ventilator should they become infected with the novel coronavirus. In contrast, people with blood type O appear to have about a 50 percent reduced risk of severe COVID-19.

These new findings—the first to identify statistically significant susceptibility genes for the severity of COVID-19—come from a large research effort led by Andre Franke, a scientist at Christian-Albrecht-University, Kiel, Germany, along with Tom Karlsen, Oslo University Hospital Rikshospitalet, Norway. Their study included 1,980 people undergoing treatment for severe COVID-19 and respiratory failure at seven medical centers in Italy and Spain.

In search of gene variants that might play a role in the severe illness, the team analyzed patient genome data for more than 8.5 million so-called single-nucleotide polymorphisms, or SNPs. The vast majority of these single “letter” nucleotide substitutions found all across the genome are of no health significance, but they can help to pinpoint the locations of gene variants that turn up more often in association with particular traits or conditions—in this case, COVID-19-related respiratory failure. To find them, the researchers compared SNPs in people with severe COVID-19 to those in more than 1,200 healthy blood donors from the same population groups.

The analysis identified two places that turned up significantly more often in the individuals with severe COVID-19 than in the healthy folks. One of them is found on chromosome 3 and covers a cluster of six genes with potentially relevant functions. For instance, this portion of the genome encodes a transporter protein known to interact with angiotensin converting enzyme 2 (ACE2), the surface receptor that allows the novel coronavirus that causes COVID-19, SARS-CoV-2, to bind to and infect human cells. It also encodes a collection of chemokine receptors, which play a role in the immune response in the airways of our lungs.

The other association signal popped up on chromosome 9, right over the area of the genome that determines blood type. Whether you are classified as an A, B, AB, or O blood type, depends on how your genes instruct your blood cells to produce (or not produce) a certain set of proteins. The researchers did find evidence suggesting a relationship between blood type and COVID-19 risk. They noted that this area also includes a genetic variant associated with increased levels of interleukin-6, which plays a role in inflammation and may have implications for COVID-19 as well.

These findings, completed in two months under very difficult clinical conditions, clearly warrant further study to understand the implications more fully. Indeed, Franke, Karlsen, and many of their colleagues are part of the COVID-19 Host Genetics Initiative, an ongoing international collaborative effort to learn the genetic determinants of COVID-19 susceptibility, severity, and outcomes. Some NIH research groups are taking part in the initiative, and they recently launched a study to look for informative gene variants in 5,000 COVID-19 patients in the United States and Canada.

The hope is that these and other findings yet to come will point the way to a more thorough understanding of the biology of COVID-19. They also suggest that a genetic test and a person’s blood type might provide useful tools for identifying those who may be at greater risk of serious illness.

References:

[1] Characteristics of and important lessons from the Coronavirus Disease 2019 (COVID-19) outbreak in China: Summary of a report of 72 314 cases from the Chinese Center for Disease Control and Prevention. Wu Z, McGoogan JM, et. al. 2020 Feb 24. [published online ahead of print]

[2] Genomewide association study of severe Covid-19 with respiratory failure. Ellinghaus D, Degenhardt F, et. a. NEJM. June 17, 2020.

Links:

The COVID-19 Host Genetics Initiative

Andre Franke (Christian-Albrechts-University of Kiel, Germany)

Tom Karlsen (Oslo University Hospital Rikshospitalet, Norway)


First Molecular Profiles of Severe COVID-19 Infections

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COVID-19 Severity Test
Credit: NIH

To ensure that people with coronavirus disease 2019 (COVID-19) get the care they need, it would help if a simple blood test could predict early on which patients are most likely to progress to severe and life-threatening illness—and which are more likely to recover without much need for medical intervention. Now, researchers have provided some of the first evidence that such a test might be possible.

This tantalizing possibility comes from a study reported recently in the journal Cell. In this study, researchers took blood samples from people with mild to severe COVID-19 and analyzed them for nearly 2,000 proteins and metabolites [1]. Their detailed analyses turned up hundreds of molecular changes in blood that differentiated milder COVID-19 symptoms from more severe illness. What’s more, they found that they could train a computer to use the most informative of the proteins and predict the disease severity with a high degree of accuracy.

The findings come from the lab of Tiannan Guo, Westlake University, Zhejiang Province, China. His team recognized that, while we’ve learned a lot about the clinical symptoms of COVID-19 and the spread of the illness around the world, much less is known about the condition’s underlying molecular features. It also remains mysterious what distinguishes the 80 percent of symptomatic infected people who recover with little to no need for medical care from the other 20 percent, who suffer from much more serious illness, including respiratory distress requiring oxygen or even more significant medical interventions.

In search of clues, Guo and colleagues analyzed hundreds of molecular changes in blood samples collected from 53 healthy people and 46 people with COVID-19, including 21 with severe disease involving respiratory distress and decreased blood-oxygen levels. Their studies turned up more than 470 proteins and metabolites that differed in people with COVID-19 compared to healthy people. Of those, levels of about 300 were associated with disease severity.

Further analysis revealed that the majority of proteins and metabolites on the list are associated with the suppression or dysregulation of one of three biological processes. Two processes are related to the immune system, including early immune responses and the function of particular scavenging immune cells called macrophages. The third relates to the function of platelets, which are sticky, disc-shaped cell fragments that play an essential role in blood clotting. Such biological insights might help pave the way for potentially effective new ways to treat COVID-19 down the road.

Next, the researchers turned to “machine learning” to explore the possibility that such molecular changes also might be used to predict mild versus severe COVID-19. Machine learning involves the use of computers to discern patterns, or molecular signatures, in large data sets that a human being couldn’t readily pick out. In this case, the question was whether the computer could “learn” to tell the difference between mild and severe COVID-19 based on molecular data alone.

Their analyses showed that a computer, once trained, could differentiate mild and severe COVID-19 based on just 22 proteins and 7 metabolites. Their model correctly classified all but one person in the original training set, for an accuracy of about 94 percent. And importantly, in further prospective validation tests, they confirmed that this model accurately identified mild versus severe COVID-19 in most cases.

While these findings are certainly encouraging, there’s much more work to do. It will be important to explore these molecular signatures in many more people. It also will be critical to find out how early in the course of the disease such telltale signatures arise. While we await those answers, I find encouragement in all that we’re learning—and will continue to learn—about COVID-19 each day.

Reference:

[1] Proteomic and metabolomic characterization of COVID-19 patient sera. Shen B et al. Cell. 28 May 2020. [Epub ahead of publication]

Links:

Coronavirus (COVID-19) (NIH)

Blood Tests (National Heart, Lung, and Blood Institute/NIH)

Tiannan Guo Lab (Westlake University, Zhejiang Province, China)