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Women With BRCA1 Gene Mutation Have Fewer Eggs in Ovaries

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Women with a mutation in the BRCA1 gene likely have fewer eggs in their ovaries than the average woman, which may shorten their window of opportunity to have children, according to a study.

The research was published online on April 23, 2021, by the Journal of Clinical Oncology. Read the abstract of “Association of Germline BRCA Pathogenic Variants With Diminished Ovarian Reserve: A Meta-Analysis of Individual Patient-Level Data.”

When a woman has fewer eggs in her ovaries than an average woman, doctors call it “diminished ovarian reserve.”

BRCA gene mutations and breast cancer
About the study
What this means for you

BRCA gene mutations and breast cancer

Two of the most well-known genes that can mutate and raise the risk of breast and ovarian cancer are BRCA1 and BRCA2. Women who inherit a mutation in either of these genes — from their mothers or fathers — have a much higher-than-average risk of developing breast cancer and ovarian cancer.

The average woman’s risk of developing breast cancer in her lifetime is about 13%. According to the National Cancer Institute (NCI), women with a BRCA1 gene mutation have between a 55% and 72% lifetime risk of developing breast cancer, while women with a BRCA2 gene mutation have between a 45% and 69% lifetime risk of developing breast cancer.

Men with these mutations — particularly a BRCA2 gene mutation — also have an increased risk of developing breast cancer and possibly an increased risk of developing prostate cancer.

About 5% to 10% of breast cancers are thought to be hereditary, meaning the cancer is linked to mutations in genes passed from parent to child.

You are substantially more likely to have a genetic mutation linked to breast cancer if:

  • your mother or blood relatives (grandmothers, sisters, aunts) on either your mother’s or father’s side of the family have been diagnosed with breast cancer before age 50
  • there is both breast and ovarian cancer on the same side of the family or in a single individual
  • you have a relative with triple-negative breast cancer
  • there are other cancers in your family in addition to breast, such as prostate, melanoma, pancreatic, stomach, uterine, thyroid, colon, and/or sarcoma
  • women in your family have had cancer in both breasts
  • you are of Ashkenazi Jewish (Eastern European) heritage
  • you are a Black woman and have been diagnosed with breast cancer at age 35 or younger
  • a man in your family has had breast cancer
  • there is a known breast cancer gene mutation in your family

Research suggests that the BRCA genes also play a role in how the ovaries function and age.

The researchers who did this study wanted to know if having a BRCA1 or BRCA2 gene mutation is linked to having fewer eggs in the ovaries.

This is important to know because young women with a BRCA1/2 gene mutation are usually advised to have their healthy breasts, ovaries, and fallopian tubes removed before age 45 to dramatically reduce their risk of breast cancer and ovarian cancer.

If a woman has fewer eggs in her ovaries, her window of opportunity to become pregnant may be shorter than average. It’s important for women who want to have children to have fertility counseling and also discuss fertility preservation options with their doctors if they are diagnosed with cancer.

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About the study

This study was a meta-analysis. A meta-analysis combines and analyzes the results of many earlier studies. In this case, the researchers reviewed five studies looking at ovarian reserve — the number of eggs in women’s ovaries — in women with BRCA gene mutations. They also contacted the authors of the five studies to see if they had any updated information.

This analysis included information on 824 women:

  • 153 women had a BRCA1 gene mutation
  • 93 women had a BRCA2 gene mutation
  • 578 women didn’t have a BRCA1/2 gene mutation

Among the 246 women with a BRCA1 or BRCA2 gene mutation, 157 (63.8%) had been diagnosed with breast cancer.

Among the 578 women without a BRCA1/2 gene mutation, 524 (90.6%) had been diagnosed with breast cancer.

The average age of the women in both groups — with and without a BRCA1/2 gene mutation — was about 34.

To determine the number of eggs in the women’s ovaries, the researchers measured levels of anti-Müllerian hormone (AMH) in the women’s blood. AMH is produced by the ovarian follicles, which are the cells that surround each egg in the ovaries. Fewer eggs mean lower AMH levels.

Average AMH levels were:

  • 2.04 ng/mL in women with a BRCA1/2 gene mutation
  • 3.36 ng/mL in women without a BRCA1/2 gene mutation

After taking into account other factors that may have affected AMH levels, the researchers found that women with a BRCA1/2 gene mutation had AMH levels that were 26% lower than women without a BRCA1/2 gene mutation. This difference was statistically significant, which means that it was likely because of the difference in mutation status and not just because of chance.

The researchers then looked to see if there were differences in AMH levels depending on the type of genetic mutation the women had.

Compared with women without a mutation, women with a BRCA1 gene mutation had 35% lower AMH levels. This difference was statistically significant.

The researchers found no difference in AMH levels in women with a BRCA2 gene mutation and women without a mutation.

In their conclusion, the researchers recommended that women with a BRCA1 gene mutation “should proactively receive reproductive and fertility preservation counseling if they are postponing childbearing to the third decade and beyond.”

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What this means for you

If you are a young woman and know you have a BRCA1 gene mutation, the results of this study are very important for you.

It’s very likely that you have fewer eggs in your ovaries than average, which can affect your fertility and your ability to have children.

It makes sense to talk to your doctor about this study and discuss how it affects your unique situation and any plans you may have for having children. You may want to ask for a referral to a fertility specialist to discuss options for fertility preservation, especially if you’ve been diagnosed with breast cancer.

Learn more about Fertility and Pregnancy Issues During and After Breast Cancer.

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Written by: Jamie DePolo, senior editor


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