Androgens, a kind of sex hormone, have been used to treat certain genetic blood disorders for decades. But doctors haven’t been able to pinpoint exactly why they seem to help some patients. A small study puts forth a theory behind androgens’ disease-fighting mechanism: They help stabilize and even rebuild telomeres, which increasingly diminish in certain conditions and aging.

Telomeres are tiny protective caps at the end of chromosomes that help keep these strands of genetic information intact from one cell division to the next. But each time a cell multiplies, part of these genetic toppers gets lost. When telomeres become too short, the DNA that cells need to function starts to get damaged and cells eventually die. This shortening process is hastened in people with dysfunctional telomeres.

Diseases related to dwindling telomeres can lead to conditions like liver cirrhosis, pulmonary fibrosis and bone marrow failure, a syndrome characterized by insufficient production of blood cells. They’re also associated with a higher risk of cancer and graying hair.

The authors of the study, published Wednesday in the New England Journal of Medicine, treated telomere-disease patients who had a variety of conditions with a high dose of a synthetic androgen called danazol. The goal was to test whether the treatment would help keep telomeres intact longer. Instead, they saw them lengthen.

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The study’s results were surprising as the researchers were only expecting the rate at which telomeres fray to slow in response to androgens.

“This is an impressive study,” said Suneet Agarwal, a bone marrow failure specialist at Boston Children’s Hospital, who wasn’t involved in the research.

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