Written by Isobel Young, Science Writer
Throughout the course of the pandemic, PCR testing has been used to identify the SARS-CoV-2 virus and to diagnose COVID-19. Despite PCR tests being accurate at detecting the virus in symptomatic patients, they have been less successful in identifying it in asymptomatic patients. Now, a case–control epigenome-wide association study from a team at the University of California suggests that analysing epigenetic changes in COVID-19 patient DNA could be the key to not only identifying the virus in asymptomatic patients, but also help us to get one step closer to understanding what causes the different clinical outcomes in COVID-19.
The study, published in Human Genomics, obtained peripheral blood samples from patients who had tested positive for COVID-19 between March 2020 and July 2020. The patients had all been admitted to the University of Colorado Hospital, and out of 644 samples collected, 164 ended up being analysed and used in this study. The samples were then analysed using the Illumina Infinium MethylationEPIC BeadChip to determine DNA methylation patterns
DNA methylation
DNA methylation occurs when an enzyme called DNA methyltransferase binds adenine and cytosine bases to methyl groups, which represses gene expression. Early in the pandemic, it was discovered that the SARS-CoV-2 virus was able to change its host’s epigenetics through DNA methylation. While the exact mechanism by which the virus triggers this methylation is unclear, this study provides us with novel insight into the impact these epigenetic changes have on the host.
Asymptomatic Vs. symptomatic patient’s methylation patterns
The study found that there was a significant difference in the DNA methylation of genes including – but not limited to – FBXO16, PSD3, and RAE1 in asymptomatic patients compared to symptomatic patients. “There is a clear pattern of methylation associated with asymptomatic SARS-CoV-2 infected patients,” the author wrote. These results could provide an explanation as to why some people infected with SARS-CoV-2 get incredibly ill, whereas some people get no symptoms at all. Furthermore, the study demonstrates how epigenetic testing could be of great use to identify the virus in asymptomatic members of the population. This could prove to be beneficial for the surveillance and containment of the virus, and thus help to prevent any further outbreaks of COVID-19.
Limitations
While this study provides the scientific community with valuable information, there are some limitations. Firstly, the samples were taken during the first few months of the pandemic; as time went on, the SARS-CoV-2 virus has mutated several times. This means the result of this study is not representative of all SARS-CoV-2 strains impact on DNA methylation, only the strains present early in the pandemic. Additionally, the study suffers from a small sample size. With only 8 asymptomatic patients compared to 156 systematic controls, future studies with larger sample sizes are required.
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