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Researchers identify genes linked to breast size

Robin Wulffson MD's picture
breast size, breast cancer, genetics, BRCA1 mutation, BRCA2 mutation

The female breast comes in a variety of shapes and sizes. Obviously genetic factors are involved in these endowments. Now, researchers have identified seven genetic markers linked with a woman’s breast size. Beyond cosmetics, their findings may provide further insight into factors involved in breast cancer risk. The study, conducted by the genetic testing company 23andMe, was published on June 30 in the journal BMC Medical Genetics.

The researchers note that some factors of breast morphology, such as density, are directly related to breast cancer risk; however, the relationship between breast size and cancer is less clear. They note that breast size is a moderately heritable trait; however, genetic variants leading to differences in breast size have not been identified. In view of this, Dr. Nicholas Eriksson and colleagues designed a study to investigate the genetic factors underlying breast size. The study group was comprised of 16,715 women of European ancestry. For this group of women, the researchers conducted a genome-wide association study (GWAS) of self-reported bra cup size, controlling for age, genetic ancestry, breast surgeries, pregnancy history, and bra band size.

The investigators identified seven single-nucleotide polymorphisms (SNPs) significantly associated with breast size. (A SNP is a DNA sequence variation occurring when a single nucleotide in the genome (or other shared sequence) differs between members of a biological species or paired chromosomes in an individual.) Two of these seven SNPs are in linkage disequilibrium (LD) with SNPs associated with breast cancer and a third is near, but not in LD with, a breast cancer SNP. In addition, the other three SNPs have strong links to breast cancer, estrogen regulation, and breast development.

The authors concluded that their results provide insight into the genetic factors underlying normal breast development and show that some of these factors are shared with breast cancer. They add that their results do not directly support any possible epidemiological relationships between breast size and cancer; however, they might contribute to a better understanding of the subtle interactions between breast morphology and breast cancer risk.

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The National Cancer Institute notes that in cross-sectional studies of adult populations, 5-10% of women have a mother or sister with breast cancer, and about twice as many have either a first-degree relative (FDR; mother, sister, or daughter) or a second-degree relative (i.e., aunt) with breast cancer. The risk increases with the number of affected relatives and age at diagnosis. Breast and ovarian cancer are components of several autosomal dominant (dominant genes) cancer syndromes. The syndromes most strongly associated with both cancers are the BRCA1 or BRCA2 mutation syndromes.

Poor lifestyle choices have also been linked to breast cancer risk. Smoking definitely increases breast. Drinking more than one or two glasses containing an alcoholic beverage may increase the risk of breast cancer. The risk of breast cancer increases with age. Most breast cancers occur in women over fifty years of age.

Other risk factors include:

  • Menstrual cycle: Women who start menstruating early (before age 12) or go through menopause late (after age 55) have an increased risk for breast cancer.
  • Childbirth: Women who have never had children or who had them only after age 30 have an increased risk for breast cancer. Being pregnant more than once or becoming pregnant at an early age reduces a woman’s risk of breast cancer.
  • Diethylstilbestrol (DES): Women who took DES to prevent miscarriage may have an increased risk of breast cancer after age 40. This drug was given to the women in the 1940s through the 1960s.
  • Hormone replacement therapy (HRT): Women who have taken HRT for several years or more have a higher risk for breast cancer.
  • Obesity: Obesity has been linked to breast cancer; however, this link is controversial. The theory is that obese women produce more estrogen, which can fuel the development of breast cancer.
  • Radiation: If a woman received radiation therapy as a child or young adult to treat cancer of the chest area, she has a significantly higher risk for developing breast cancer. The younger the radiation therapy was given and the higher the dose, the higher the risk––especially if the radiation was given when a female was developing breasts.

Reference: BMC Medical Genetics

See also:
Reduce your breast cancer risk with exercise
FDA accelerates drug approval for patients with aggressive breast cancers