By Haley Fuoco
You may have heard that individuals with Jewish ancestry have a greater risk of BRCA mutations, linked to breast and ovarian cancers, and other types of cancer. But did you know that not all mutations in the BRCA genes are the same? There are actually around 2,000 variations (a technical term for genetic differences) of BRCA1 and around 3,000 variations of BRCA2. These variations are formally known as Single Nucleotide Polymorphisms, or SNPs.
The term polymorphism describes two or more changes in a particular DNA sequence that arise from heritable mutations and act as genetic markers in the DNA. As the name suggests, a SNP is a type of variation at a single base pair in the DNA sequence.
An example of a SNP might look like the DNA strands below:
where the G and the C base pairs represent different versions of a particular DNA sequence. Even though SNPs are common, and they arise from mutations, they typically do not cause changes to the DNA that lead to disease.
Scientists and healthcare providers can learn more about certain genetic disorders, as well as genetic lineage, by examining SNPs. Since SNPs are heritable, they can often track the inheritance of diseases in families or populations. One specific example of this is with BRCA1 and BRCA2 mutations in individuals with Ashkenazi Jewish ancestry. About one in 40 individuals with Ashkenazi Jewish ancestry carry a BRCA mutation. And despite the many different types of BRCA mutations caused by SNPs, most individuals with Ashkenazi Jewish ancestry with a BRCA mutation have the same type. Why is this the case?
This occurrence is likely caused by the founder effect, a concept that suggests that individuals with Ashkenazi Jewish ancestry can trace their ancestry back to a small group of “founders” who lived 500 years ago in Eastern Europe. SNPs allow scientists to trace Ashkenazi Jewish ancestry back to the founder population. The founder effect explains why individuals of Jewish ancestry have the same BRCA1 or BRCA2 SNPs. Therefore, not all BRCA mutations are the same, but some BRCA mutations might be more common in individuals with similar ancestry.