single nucleotide variants
More Genetic Clues to COVID-19 Susceptibility and Severity
Posted on by Dr. Francis Collins
Many factors influence our risk of illness from SARS-CoV-2, the coronavirus responsible for COVID-19. That includes being careful to limit our possible exposures to the virus, as well as whether we have acquired immunity from a vaccine or an earlier infection. But once a person is infected, a host of other biological factors, including age and pre-existing medical conditions, will influence one’s risk of becoming severely ill.
While earlier studies have tied COVID-19 severity to genetic variations in a person’s antiviral defenses and blood type, we still have a lot to learn about how a person’s genetic makeup influences COVID-19 susceptibility and severity. So, I was pleased to see the recent findings of an impressive global effort to map the genetic underpinnings of SARS-CoV-2 infection and COVID-19 severity, which involved analyzing the genomes of many thousands of people with COVID-19 around the globe.
This comprehensive search led to the identification of 13 regions of the human genome that appear to play a role in COVID-19 infection or severity. Though more research is needed to sort out these leads, they represent potentially high-quality clues to the pathways that this virus uses to cause illness, and help to explain why some people are more likely to become infected with SARS-CoV-2 or to develop severe disease.
The international effort, known as The COVID-19 Host Genetics Initiative, is led by Andrea Ganna, Institute for Molecular Medicine Finland, Helsinki, and colleagues in the United States and around the world. Teasing out those important genetic influences is no easy task. It requires vast amounts of data, so Ganna reached out to the scientific community via Twitter to announce a new COVID-19 gene-hunting effort and ask for help. Thousands of researchers around the world answered his call. The new study, published in the journal Nature, includes data collected through the initiative as of January 2021, and represents nearly 50,000 COVID-19 patients and another 2 million uninfected controls [1].
In search of common gene variants that may influence who becomes infected with SARS-CoV-2 and how sick they will become, Ganna’s international team turned to genome-wide association studies (GWAS). As part of this, the team analyzed patient genome data for millions of so-called single-nucleotide polymorphisms, or SNPs. While these single “letter” nucleotide substitutions found all across the genome are generally of no health significance, they can point the way to the locations of gene variants that turn up more often in association with particular traits or conditions—in this case, COVID-19 susceptibility or severity. To find them, the researchers compared SNPs in people with COVID-19 to those in about 2 million healthy blood donors from the same population groups. They also looked for variants that turned up significantly more often in people who became severely ill.
Their analyses uncovered a number of gene variants associated with SARS-CoV-2 infection or severe COVID-19 in 13 regions of the human genome, six of which were new. Four of the 13 affect a person’s risk for becoming infected with SARS-CoV-2. The other nine influence a person’s risk for developing severe illness following the infection.
Interestingly, some of these gene variants already were known to have associations with other types of lung or autoimmune diseases. The new findings also help to confirm previous studies suggesting that the gene that determines a person’s blood type may influence a person’s susceptibility to SARS-CoV-2 infection, along with other genes that play a role in immunity. For example, the findings show overlap with variants within a gene called TYK2, which was earlier shown to protect against autoimmune-related diseases. Some of the variants also point to the need for further work to study previously unexplored biological processes that may play potentially important roles in COVID-19.
Two of the new variants associated with disease severity were discovered only by including individuals with East Asian ancestry, highlighting the value of diversity in such analyses to gain a more comprehensive understanding of the biology. One of these newfound variants is close to a gene known as FOXP4, which is especially intriguing because this gene is known to play a role in the airways of the lung.
The researchers continue to look for more underlying clues into the biology of COVID-19. In fact, their latest unpublished analysis has increased the number of COVID-19 patients from about 50,000 to 125,000, making it possible to add another 10 gene variants to the list.
Reference:
[1] Mapping the human genetic architecture of COVID-19. COVID-19 Host Genetics Initiative. Nature. 2021 Jul 8.
Links:
COVID-19 Research (NIH)
Genome Data from Africa Reveal Millions of New Variants
Posted on by Dr. Francis Collins
The first Homo sapiens emerged in Africa hundreds of thousands of years ago. We are all descended from that common pool of ancestors. Put another way, we are all Africans. While it’s not possible to study the DNA of these vanished original human populations, it is possible to study the genetic material of today’s African peoples to learn more about the human genome and its evolution over time. The degree of genetic diversity in Africa is greater than anywhere else in the world.
Progress continues to be made in this important area of genomic research. The latest step forward is a study just published in the journal Nature that analyzes more than 400 complete human genomes, including 50 distinct groups of people from 13 African countries. This work has uncovered about 3.4 million unique gene variants that had never before been described, greatly expanding our knowledge of human genetic variation and its implications for health and disease.
This work is the latest from the Human Heredity and Health in Africa (H3Africa) Initiative , which I helped establish a decade ago. This partnership between NIH, the Wellcome Trust, and the Alliance for Accelerating Excellence in Science in Africa (AESA) seeks to train a new generation of African scientists in genomic science and other disciplines, while conducting state-of-the-art health research on the African continent. The hope is to help these scientists use their new knowledge to improve human health in Africa and to help fill significant gaps in our knowledge of the diversity within human genomes.
The new study was led by Zané Lombard, the University of the Witwatersrand, South Africa; Neil Hanchard, Baylor College of Medicine, Houston; and Adebowale Adeyemo, NIH’s National Human Genome Research Institute, Bethesda, MD. It also included more than 50 other H3Africa data providers and data analysts from across Africa and around the world.
These researchers sequenced and analyzed the genomes of 426 individuals, almost all from studies and countries within the H3Africa Consortium, the network of NIH and Wellcome Trust-funded research sites in Africa. These individuals were carefully selected to provide broad coverage of the diverse landscape of African genomic variation. They also included many populations that hadn’t been studied at the genetic level before. The team focused its attention on single-letter differences, also known as single nucleotide variants (SNVs), located across the 3 billion DNA letters of the human genome.
All told, the researchers observed more than 31 million confirmed SNVs. Of the 3.4 million newly discovered SNVs, most turned up in the genomes of individuals from previously unstudied African ethnic groups with their own distinct languages. Even among SNVs that had been previously reported, several were found much more often than in other populations. That’s important because medical geneticists often include information about frequency in deciding whether a gene variant is a likely cause of rare disease. So, this more complete picture of normal genetic variation will be valuable for diagnosing such genetic conditions around the globe.
The researchers also found more than 100 regions of the genome where the pattern of genetic variation was suggestive of underlying variants that were evolutionarily favored at some time in the past. Sixty-two of those chromosomal locations weren’t previously known to be under such strong natural selection in human populations. Interestingly, those selected regions were found to contain genes associated with viral immunity, DNA repair, reproduction, and metabolism, or occurred close to variants that have been associated with conditions such as uterine fibroids and chronic kidney disease.
The findings suggest that viral infections, such as outbreaks of Ebola, yellow fever, and Lassa fever, may have played an important role over centuries in driving genetic differences on the African continent. The data also point to the possibility of human adaptation to differences across the African continent in local environments and diets, and these adaptations could be relevant to common diseases and traits we see now.
The researchers used the data to help gain insight into past migrations of human populations. The genetic data revealed complex patterns of ancestral mixing within and between groups. It also uncovered how distinct groups likely moved large distances across Africa in the past, going back hundreds to thousands of years. The findings also offered a more complete picture of the timing and extent of the migration of speakers of Africa’s most common language group (Bantu) as they moved from West Africa to the southern and eastern reaches of the continent—a defining event in the genetic history of Africa.
There’s still much more to learn about the diversity of human genomes, and a need for continued studies, including many more individuals representing more distinct groups in Africa. Indeed, H3Africa now consists of 51 projects all across the continent, focused on population-based genomic studies of many common health conditions, from heart disease to tuberculosis. As the cradle of all humanity, Africa has much to offer genomic research in the years ahead that will undoubtedly have far-reaching implications for people living in all parts of our planet.
Reference:
[1] High-depth African genomes inform human migration and health. Choudhury A et al. 2020 Oct;586(7831):741-748.
Links:
Human Heredity and Health in Africa (H3Africa) (NIH)
H3Africa (University of Cape Town, South Africa)
NIH Support: National Human Genome Research Institute; National Institute of Allergy and Infectious Diseases
