Since 1994, scientists have known that having a mutated version of the BRCA1 gene greatly heightens a person's risk of breast cancer. Healthy BRCA1 encodes a cancer-suppressing protein that aids in DNA repair. Scientists have noted a scarcity of the protein in women who have breast cancer but don't have a family history of the disease or the BRCA1 mutation.
Researchers now report that some of these breast cancer patients nevertheless have an incapacitated BRCA1. Although the gene itself remains intact, a nearby stretch of DNA that switches on the gene has become impaired. The culprit is hypermethylation, a state in which too many methyl groups—hydrocarbon fragments—latch onto a specific DNA region. In some breast cancer patients, hypermethylation disables the control, or promoter, region for BRCA1 and silences the gene such that it can't direct production of its protein.
Cells routinely coat DNA with methyl groups