U.S. Coronavirus Cases Soar as 18 States Set Single-Day Records This Week

A preliminary report on four Covid-19 patients published in the medical journal JAMA offers intriguing clues about why some healthy young men become severely ill from the infection, and why men in general are more prone than women to serious effects of the disease.

Very rare genetic defects that weaken the immune system may have played havoc in the four patients — two sets of brothers ages 21 to 32 from unrelated families in the Netherlands. All, previously in good health, were admitted to intensive care units between March 23 and April 25. One, age 29, died.

Genetic analyses of the patients and their families identified flaws in a gene that enables cells to make molecules called interferons, which stir the immune system to fight off viruses. Without this line of defense, the researchers speculated, the patients struggled to fight the infection.

These genetic defects they were found to have are too rare to account for many other inexplicably severe cases of Covid-19, the researchers said, but the findings point to the possibility that other genetic variations may also influence susceptibility.

The findings also offer hints about why men in general may be more vulnerable than women to severe cases of Covid-19.

The gene that was flawed in the four young men in the study is located on the X chromosome. Men have one copy of that chromosome, while women have two — and if one X in a woman carries the gene defect, her other X may have a normal form of the gene, enabling the creation of enough interferons to stay healthy.

Having two copies of the normal gene — as most women do — may also give them an advantage over men.

An editorial accompanying the report said additional studies like this one could help explain how the disease develops, and enable researchers to find better treatments.