RNA molecules aren’t always faithful reproductions of the genetic instructions contained within DNA, a new study by University of Pennsylvania Medical School shows. The finding seems to violate a central dogma of genetics: DNA letters encode information and RNA is made in DNA’s likeness; the RNA then serves as a template to build proteins.

They found that RNA molecules contained misspellings at 20,000 different places in the genome, with about 10,000 different misspellings occurring in two or more of the people studied. The consequences of the misspellings are unknown.