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If you’re an identical twin who’s always resisted being called a clone of your sibling, scientists say you have a point. Identical twins are not exactly genetically the same, new research shows. Scientists in Iceland sequenced DNA from 387 pairs of identical twins — those derived from a single fertilized egg — as well as from their parents, children and spouses. That allowed them to find “early mutations that separate identical twins,” said Kari Stefansson, a geneticist at the University of Iceland and the company deCODE genetics, and co-author of the paper published Thursday in the journal Nature Genetics. (Larson, 1/7)

The results of a large observational study suggest fluoroquinolone antibiotics are associated with an increased short-term risk of aortic aneurysm. The study, published yesterday in JAMA Surgery, found that aortic aneurysm incidence within 90 days of filling a fluoroquinolone prescription was 20% higher in adults 35 and over compared with other antibiotics. In particular, there was a 31% higher incidence of abdominal aortic aneurysm and a 61% higher incidence of iliac artery aneurysm after fluoroquinolone use. (Dall, 1/7)

The technology used in a pair of pioneering Covid-19 vaccines works by effectively revving up the immune system to fight off the virus that causes the disease. But what if that same approach could be used to turn the immune system down to treat autoimmune disorders? (Garde, 1/7)

When I entered public service in 1991 as a research scientist with the Environmental Protection Agency, its attention was focused on the impact of pesticides and industrial chemicals on humans and wildlife. A breakthrough came eight years later with an article I wrote with my colleague Thomas Ternes describing what would eventually become known as the exposome — the totality of exposure over time to all stressors, chemical and nonchemical alike. (Christian Daughton, 1/7)