Large cohorts
Genomic and computer resources allow for the study of large sets of data from thousands of individuals. In each of those sets of data, the signal offered by thousands of markers distributed throughout the genome can be studied. This is the possibility offered by various genomic studies of large cohorts of patients with different clinical manifestations.
“Researchers examine thousands of genetic variants throughout the genome from a large sample of individuals and have the chance, for example, to identify genetic variants that are more prevalent in patients who have presented with severe disease than in those who presented with milder disease,” said Dr. Krieger. “These associations highlight a chromosome region in which one or more genes explain, at least in part, the differences observed.”
Genomewide association studies have identified some genetic variants that indicate severity of COVID-19, with potential impact on the virus entering the cell, the immune response, or the development of cytokine storms.
One of these studies, COVID-19 Host Genetics Initiative (COVID-19 HGI), is an international, open-science collaboration for sharing scientific methods and resources with research groups across the world, with the goal of robustly mapping the host genetic determinants of SARS-CoV-2 infection and the severity of the resulting COVID-19 disease. At the start of 2021, the COVID-19 HGI combined genetic data from 49,562 cases and 2 million controls from 46 studies in 19 countries. A total of 853 samples from the BRACOVID study were included in the meta-analysis. The endeavor enabled the identification of 13 genomewide significant loci that are associated with SARS-CoV-2 infection or severe manifestations of COVID-19.
The BRACOVID study, in which Dr. Krieger participates, aims to identify host genetic factors that determine the severity of COVID-19. It is currently the largest project of its kind in Latin America. An article provides the analysis of the first 5,233 participants in the BRACOVID study, who were recruited in São Paulo. Of these participants, 3,533 had been infected with COVID-19 and hospitalized at either the Heart Institute or the Central Institute of the FMUSP General Hospital. The remaining 1,700 made up the control group, which included health care professionals and members of the general population. The controls were recruited through serology assays or PCR tests for SARS-CoV-2.
The researchers discovered a region of chromosome 1 that could play a role in modulating immune response and that could lead to an increase in the likelihood of hospitalization across a wide range of COVID-19 risk factors. This region of chromosome 1 was observed only in Brazilians with a strong European ancestry; however, this finding had not been mentioned in previous studies, suggesting that it could harbor a risk allele specific to the Brazilian population.
The study also confirmed most, but not all, of the regions recorded in the literature, which may be significant in identifying factors determining severity that are specific to a given population.
Including information from the BRACOVID study, other studies have enhanced the knowledge on affected organs. Combined data from 14,000 patients from nine countries evaluated a region of a single chromosome and found that carriers of a certain allele had a higher probability of experiencing various COVID-19 complications, such as severe respiratory failure, venous thromboembolism, and liver damage. The risk was even higher for individuals aged 60 years and over.