The discovery may change how scientists read the instructions contained in DNA and interpret mutations to make sense of health and disease.
Since the genetic code was deciphered in the 1960s, researchers have assumed that it was used exclusively to write information about proteins.
University of Washington scientists were surprised to discover that genomes use the genetic code to write two separate languages.
One describes how proteins are made, and the other instructs the cell on how genes are controlled. One language is written on top of the other, which is why the second language remained hidden for so long.
"Now we know that this basic assumption about reading the human genome missed half of the picture. These new findings highlight that DNA is an incredibly powerful information storage device, which nature has fully exploited in unexpected ways," he said.
The genetic code uses a 64-letter alphabet called codons. The UW team discovered that some codons, which they called duons, can have two meanings, one related to protein sequence, and one related to gene control.
The discovery of duons has major implications for how scientists and physicians interpret a patient's genome and will open new doors to the diagnosis and treatment of disease.
"The fact that the genetic code can simultaneously write two kinds of information means that many DNA changes that appear to alter protein sequences may actually cause disease by disrupting gene control programs or even both mechanisms simultaneously," said Stamatoyannopoulos.