SNPwatch: Researchers Identify Variant Associated with Breast Density

Editor’s note: Pending an FDA decision, 23andMe no longer offers new customers access to health reports referred to in this post. Customers who purchased prior to November 22, 2013 will still be able to see their health reports, but those who purchased after that time will not. Those customers will have access to ancestry information as well as access to their uninterpreted raw data.

Mammography is a common imaging method used to screen for breast cancer, the second most common cancer in women. The result of a mammogram is a simple black and white image of the tissues that make up the breast. But even an image displaying apparently healthy breast tissue may still show signs that could be useful in assessing risk for breast cancer. It turns out that density — the proportion of dense (white) areas that appear on a mammogram — matters. In the last decade, research has revealed that women with high mammographic density (>75% dense tissue on a mammogram) have four to five times higher risk for breast cancer.

Characteristics such as age and BMI can affect mammographic density, but it’s estimated that over 60% of the variability in mammographic density is due to genetic factors. In an effort to identify these genetic factors, a multi-national team of researchers searched for genetic variants linked to this trait in 7,712 European women with known breast density. In results published recently in Nature Genetics, the researchers identified a variant in a gene called ZNF365 that is correlated with breast density. They found that each copy of an A at was associated with a 2% decrease in mammographic density. The researchers also found that each copy of an A at is also associated with slightly lower odds of developing breast cancer. This association of with breast cancer replicated a similar result found by another research group in 2010.

(23andMe customers can view their results for mammographic breast density in their Breast Cancer Risk Modifiers report, or check their data for using the Browse Raw Data feature.)

While the authors state that the effects of may only account for a fraction of the of the variability in mammographic density, they note that this seemingly small decrease in density is also associated with a meaningful decrease in breast cancer risk. Although the data from this study suggests that genetic variation in ZNF365 could be affecting breast cancer risk by influencing mammographic density, further research is required to confirm this finding and to determine the other genetic factors that are involved.

SNPwatch gives you the latest news about research linking various traits and conditions to individual genetic variations. These studies are exciting because they offer a glimpse into how genetics may affect our bodies and health; but in most cases, more work is needed before this research can provide information of value to individuals. For that reason it is important to remember that like all information we provide, the studies we describe in SNPwatch are for research and educational purposes only. SNPwatch is not intended to be a substitute for professional medical advice; you should always seek the advice of your physician or other appropriate healthcare professional with any questions you may have regarding diagnosis, cure, treatment or prevention of any disease or other medical condition.


  • faye

    This post has touched very close to home for me.
    My history in a nutshell: at age 31 I felt a lump. The doctors couldnt feel anything, but sent me for a mammogram. The mammographer told me I had “perfect breasts” and they only found the cancer 2 years later (even though I pinpointed it). I was treated at Sloane Kettering in NYC where I filled out many questionnaires, and while I checked “no” to every risk factor (no miscarriages, 3 breastfed children, 2 healthy grandmas) one questionnaire asked about breast density. I was told I had extremely dense breasts which is why they couldnt see the tumor. It was explained as a “chicken and egg” thing, maybe more young women with dense breasts get cancer bc it isnt diagnosed with a mammogram. I had genetic testing, and although I was told I am BRCA negative, I know there must be some genetic component that is not yet understood.

    I imagine for the future websites like this having categories under the “health” icon for a variety of illnesses and diseases, where individual volunteers can contribute their information. The ability to sort and analyze large numbers of genetic data can shed light on health and prevention. I would love to reach out to young women recently diagnosed with breast cancer and have a sort of “get out the dna” campaign. I have seen too many young moms die of breast cancer and the government sponsored research seems to be moving too slow.

    My daughter is turning 19 and heading off to college. Once you have breast cancer you spend most of your life worrying about recurrence. My hope for her that her ability to prevent cancer in the first place will offer her a much better quality of life.

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