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One of the mysteries of the coronavirus pandemic that scientists are trying to solve is why some people are barely affected while others who seem to be young and healthy become very sick.
As researchers have continued to study the virus, one area of consideration is patients' genes.
In general, the profile of a COVID-19 patient likely to experience severe symptoms is older, typically with underlying illnesses, and probably male.
However, a small percentage of patients being treated around the world are under the age of 50 and have no underlying medical issues.
Geneticist Jean-Laurent Casanova, director of the human genetics of infectious diseases laboratory jointly based at the Imagine Institute in Paris and Rockefeller University in New York City, is focused on that smaller group of patients.
"Someone who could have run the marathon in October 2019 and yet in April 2020 is in intensive care, intubated and ventilated," he told the AFP, adding that the goal is to discover any potential genetic mutations they may have.
Casanova co-founded the COVID Human Genetics Effort, which is seeking to study the genome of these severely ill younger patients in places such as China, Iran, Europe, North America and Japan.
"The assumption is that these patients have genetic variations that are silent until the virus is encountered," he explained.
Scientists involved in the global effort are also looking at people who do not become infected despite repeated exposure.
The COVID Human Genetics Effort is one example of a worldwide push to scrutinize the genomes of patients with the deadly virus for potential variations that could explain why some people quickly get very sick and others do not.
The ultimate goal is to find information that leads to new, effective treatments.