Research on twins indicates strong genetic influences in COVID-19

As of October 7, 2021, the 2019 coronavirus disease (COVID-19) had killed more than 4.82 million people worldwide. The need to identify factors associated with the spread and virulence of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), which is the virus responsible for COVID-19, has sparked numerous studies.

New study published on the preprint server medRxiv * discusses the strong possibility of multifactorial causation for SARS-CoV-2 infection using data from twin studies.

To study: “COVID-19 in Twins: What Can We Learn From Them? “ Image Credit: Marian Weyo / Shutterstock.com

Background

The emergence of SARS-CoV-2 in Wuhan, China at the end of 2019 was followed by the rapid development of several vaccines aimed at stopping community transmission of SARS-CoV-2 by increasing the level of collective immunity. Vaccine efficiency has since been called into question by the emergence of new variants of SARS-CoV-2 more transmissible and sometimes more virulent than the ancestral strain.

In addition, some variants of SARS-CoV-2 are able to escape neutralization by antibodies caused by previous exposure to ancestral viral antigens, either by natural infection or by vaccination. These strains are called variants of concern (VOCs).

Previous studies on the pathogenesis and severity of COVID-19 have included comparisons of infection rate, severity, and adverse outcomes in pairs of monozygotic (MZ) and dizygotic (DZ) twins, as with others. infectious pathogens. The goal is to detect a genetic component, if any, that contributes to susceptibility.

The overall risk of disease or infection in a pair of twins will be equal if the susceptibility is determined primarily by environmental factors. Conversely, the presence of a genetic component will be demonstrated by a higher degree of similarity in results in MZ twins, who have identical genetic codes, compared to DZ twins, who have only fraternal degrees of genetic programming. shared.

The current group of researchers have already shown that the clinical features of post-infectious Zika Congenital Syndrome (ZCS) in members of twin pairs were inconsistent with the genetic makeup of the twin baby. This despite the fact that both had been exposed to the virus during pregnancy.

In the case of COVID-19, such a direct comparison is difficult because members of a pair of twins may not be equally exposed, in addition to the extreme variation in clinical manifestations. Some infected people are completely asymptomatic, while others develop serious illness or even die of the disease, regardless of their age.

Since an early stage, illness and death of identical twins from COVID-19 have been reported, with both dying within days or hours of each other. It started with a set of adult MZ twins who died three days apart in April 2020. It has raised questions about the involvement of genetic components in this disease. in close succession.

This article discusses the outcome of COVID-19 in ten pairs of twins, half of which were MZ twins and the other half DZ. All of the twins included in this study were from the city of Sao Paulo, Brazil.

Study results

Among the pairs of twins, at least one in each pair had tested positive for COVID-19. The two twins shared a bedroom and did not use any measures to protect themselves against the virus at home. In the majority of cases, the infected twin had contracted the infection from one or more parents.

The researchers found that four out of five pairs of MZ twins had a match for infection. That is, the two twins were either symptomatic or asymptomatic. However, the reverse was true for all five pairs of DZ twins, with four of them showing a mismatch.

In the only pair of MZ twins that did not show a match, both were infected and presented symptoms of COVID-19. However, one was re-infected and developed severe illness, while the other had only one episode of infection with mild symptoms.

This corroborates the findings of previous reports on pairs of adult MZ twins with discordant clinical presentations.

In one case, the twins had several common medical conditions, including type 2 diabetes, hypertension, and higher body mass index (BMI) values. Surprisingly, the twin with more medical complications had a milder, shorter episode, while the other was hospitalized with critical COVID-19.

In another, the individuals were in good health but one developed critical COVID-19 requiring mechanical ventilation, while the other quickly recovered from mild bouts. This is the case even in congenital infections with pathogens, such as human immunodeficiency virus (HIV) or cytomegalovirus, where MZ twins exposed to the same virus in utero nevertheless develop different clinical diseases.

On the other hand, Brazilian media reported seven or more identical pairs of twins who died within days or weeks of each other. Of these, six pairs were males, which is consistent with the known increased risk of severe COVID-19 in this sex. However, these twins did not stay together and did not have any underlying illnesses. This indicates that genetic factors play a major role in the concordant clinical course.

Conclusion

“In conclusion, although these observations are derived from a small sample, the rate of discordance between DZ twins and the higher concordance in MZ give more evidence of a complex multifactorial inheritance modulating susceptibility or resistance to infection. by SARS-CoV-2. “

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer reviewed and, therefore, should not be considered conclusive, guide clinical practice / health-related behavior, or treated as established information.