What is the BRCA Mutation Rate in Ashkenazi Jews?

If you have any Ashkenazi Jewish ancestry, you are significantly more likely to carry a mutation in the BRCA1 or BRCA2 genes than people in the general population ^[1]. About 1 in 40 individuals of Ashkenazi Jewish descent carries a BRCA mutation (approximately 2.5%), compared to about 1 in 400 people in the general population ^[1].

This difference is due to population genetics and a phenomenon known as the founder effect.

Understanding the Founder Effect

The founder effect happens when a small group of individuals separates from a larger population to establish a new, isolated community ^[2][3]. If even a few individuals in that original “founding” group happen to carry a specific genetic mutation, that mutation can become much more common as the population grows over generations, because they generally marry and have children within their own community ^[2].

For the Ashkenazi Jewish population, historical events led to a smaller ancestral group that grew rapidly over centuries. As a result, certain genetic traits—including specific changes in the BRCA1 and BRCA2 genes—became concentrated and are seen at much higher rates today ^[3].

The Three Founder Mutations

In the Ashkenazi Jewish population, almost all BRCA mutations involve just three specific genetic changes, collectively known as the founder mutations ^[1]:

• 185delAG (in the BRCA1 gene)
• 5382insC (in the BRCA1 gene)
• 6174delT (in the BRCA2 gene)

(Note: You may see these listed differently on modern lab results, such as c.68_69delAG instead of 185delAG).

These three specific mutations account for the majority of hereditary breast and ovarian cancers in families of Ashkenazi descent ^[1].

What This Means for Testing and Cancer Risk

The presence of any of these mutations significantly increases a person’s lifetime risk of developing certain cancers. The risk depends on which specific gene is affected:

• Breast cancer: By age 80, the risk is about 72% for BRCA1 carriers and 69% for BRCA2 carriers ^[4].
• Ovarian cancer: By age 80, the risk is approximately 44% for BRCA1 carriers and 17% for BRCA2 carriers ^[4].
• Other cancers: Prostate cancer, pancreatic cancer, and male breast cancer are also linked to these genes. For instance, BRCA2 mutations are associated with a particularly higher risk of aggressive prostate cancer compared to BRCA1 ^[4].

While these numbers can be intimidating, knowing your mutation status is highly empowering. Identifying a mutation before cancer develops allows you and your care team to take proactive steps, such as starting enhanced screenings (like breast MRIs) at an earlier age, discussing risk-reducing surgeries, or individualizing how a detected cancer is managed ^[5].

Because these specific mutations are so well understood, genetic testing for individuals with Ashkenazi Jewish heritage often begins by looking specifically for these three variants ^[2]. However, it is also important to note that individuals of Ashkenazi descent can occasionally carry other, non-founder mutations in BRCA1, BRCA2, or other cancer susceptibility genes ^[6][7]. For this reason, doctors or genetic counselors may sometimes recommend a more comprehensive multigene panel rather than just checking for the three founder mutations ^[6].