Twins with Covid Help Scientists Untangle the Disease’s Genetic Roots - The New York Times

“I want to know,” one twin said, “why did she have Covid worse than me?”.

After 35 years of sharing everything from a love for jazz music to tubes of lip gloss, twins Kimberly and Kelly Standard assumed that when they became sick with Covid-19 their experiences would be as identical as their DNA.

While Kelly was discharged after less than a week, her sister ended up in intensive care.

Weeks after Kelly had returned to their shared home, Kimberly was still relearning how to speak, walk and chew and swallow solid food she could barely taste.

“I want to know,” Kelly said, “why did she have Covid worse than me?”.

These studies have also underscored the importance of the environment and pure chance: Even between identical twins, immune systems can look vastly different — and continue to grow apart over the course of a lifetime.

Mishita Goel, one of the doctors who treated the Standard twins last spring, said she was surprised to see the virus chart such different medical trajectories in each sister.

Still, in at least some respects, the bodies of identical twins are “genetically programmed to be similar.”.

Miller said of her sister.

“It’s the difference between having your immune system being actually able to squash the infection, or having a much harder time fighting it if all your cells become infected at the same time,” said Juliet Morrison, a virologist at the University of California, Riverside.

Marena and Vivian Herr, 17-year-old identical twins in Jackson Hole, Wyo., have spent their entire lives near each other, bonding over their tastes for In-N-Out Burger and Taylor Swift.

Identical twins start as a single embryo that splits in two, creating carbon-copy babies-to-be.

Even the DNA that cells start with is not set in stone.

Certain immune cells called B cells and T cells are, in some ways, especially impervious to the genes they start with.

Instead, immune cells build their defensive repertoires through a process called recombination, which involves mixing and matching segments of DNA to create billions, trillions, even quadrillions of unique genetic stretches.

Marion Pepper, an immunologist at the University of Washington and the identical twin sister of Anita Pepper, compared the process to cobbling together words on a Scrabble board — a way to generate a diverse vocabulary without hauling a dictionary from place to place.

This immune malleability is an advantage, because it can equip the body to fend off even pathogens it has never seen before, said Mark Davis, an immunologist at Stanford University who has used his institution’s twin registry to conduct research on the genetics of the immune system.

Emanuela Medda, a researcher with the Italian Twin Registry, is leading an effort to track stress, anxiety and depression among thousands of twins scattered countrywide.

In Michigan, Kimberly and Kelly Standard recall their sicknesses last spring as one of the longest stretches they’ve ever spent apart

It was a blessing, Kimberly said: “Finally, it felt like I was myself again.”