What is a founder mutation? 

A founder mutation is a genetic change/mutation that appeared hundred of years ago in a population that afterward remained genetically isolated. 

This could be due, for example, to geography (islanders) or religion (Mormons or Jewish groups).  

As result, the founder mutation spreads, passing from generation to generation, mostly within this population where it exists in much higher numbers than on the outside. And in fact, today we find mutations that are more common in certain populations than others, some associated with hereditary breast cancer.

In the United States, two mutations in the BRCA1 gene, and one in the BRCA2 gene, are linked with hereditary breast cancer in Ashkenazi Jews.

In Portugal, the founder mutation in the BRCA2 gene was identified in families from the center and the north of the country, and led to the development of a specific breast cancer. 

Interestingly, the Portuguese mutation seems to have appeared around 2400 years ago.
Because of this, it is believed to have now spread to Portuguese families outside of the initial circle, as well as to descendants of Portuguese sailors, merchants and emigrants spreading all over the world.

The discovery of a founder mutation in a population allows a much better understanding of the hereditary breast cancer in that population.

The main advantage, though, is an improvement in diagnosis.

This because instead of the traditional genetic tests that look at the entire BRCA genes, once a founder mutation is identified in a population, high-risk families can be tested for errors in the founder mutation area. in this case a positive diagnosis would be faster and cheaper than if running traditional tests.

If the result is negative, though, the families will still have to be tested for the whole of the BRCA1 and BRCA2 genes by the more comprehensive and complex traditional methods.

If your doctor suspects a hereditary mutation in your family, but you do not have any relative with the disease alive or willing to be tested for BRCA mutations, ask your doctor about founder mutations.