Researchers at a commercial DNA testing service say they have found a handful of genes that help determine whether a woman spends her life as an A cup or a D.
Those genes might also be tied, they say, to a woman's risk of breast cancer.
"There are surprising connections between some of the genes involved in determining breast size and the genes involved in breast cancer," lead author Nick Eriksson, a researcher with the California-based personal genomics company 23andMe, told The Huffington Post.
In a study published in the journal BMC Medical Genetics, Eriksson and his colleagues analyzed data from more than 16,000 female customers who had previously had their genetic makeup examined. The researchers were looking for single nucleotide polymorphisms, or SNPs, which are variations in DNA that occur when a single nucleotide in a sequence is altered. Some SNPs have no impact on cell function; others can predispose people to certain traits or illnesses.
After comparing the women's genetic data with information they provided about their bra size, researchers identified seven SNPs as "significantly associated" with breast size, three of which have been previously linked to breast cancer risk.