What are genes and genetic mutations?

What are genes?

Genes contain the blueprint of all hereditary information. Our genes are made up of building blocks called DNA, which make up each individual. Each gene corresponds to a unique set of instructions.  There are many thousands of different genes, each carrying a different instruction.

What are BRCA genes and what do they do?

We all carry BRCA1 and BRCA2 genes.  We get a copy of each from our parents and their function is to suppress tumours and repair DNA that has been damaged. If you carry a fault or alteration (called a ‘mutation’) in your BRCA gene, you are at a higher risk of developing certain cancers. This is because your faulty BRCA gene is not able to carry out its DNA repair function.

Although people often associate BRCA mutations with women’s cancers, both women and men can carry them and their children have a 50% chance of inheriting a mutation from the affected parent.

To understand how a gene functions and how a mutation may be passed on to your children watch this animation from Breast Cancer Now.

How common are BRCA mutations?

In the general population around 1 in 300-400 people carry a harmful BRCA mutation.  There are some groups of individuals in whom BRCA mutations occur more commonly. One such example is the Ashkenazi Jewish population 1 in 40 of whom carry a fault in the BRCA gene. Other examples of populations in whom BRCA mutations are more frequent include people of Norwegian, Icelandic, Polish, Dutch, Swedish, Finnish, Scottish, Irish and Bahamian origin.

Amongst these groups of people, there are certain mutations that are found more commonly in these particular communities, which are called founder mutations – this refers to an altered gene that affects a significant proportion of people in that community and can often be traced to a single identifiable ancestor.

The three founder mutations that are found in the Ashkenazi Jewish community are:

  • 185delAG in BRCA1
  • 5382insC in BRCA1
  • 6174delT in BRCA2

You will be given a code similar to the one above when you receive confirmation that you carry a BRCA mutation. The numbers refer to where on the chromosome your mutation occurs and what kind of mutation it is.  As genetic testing becomes more advanced, researchers will be able to identify that certain mutations infer an increased risk of specific cancers.

If you are interested in learning more about what your mutation code means, ‘Brave Bosom’ has a fantastic blog post on her site which explains it in easy to understand terms.

Who is at risk of carrying a BRCA gene mutation?

Certain groups of people are at risk of carrying a BRCA mutation and should therefore be more vigilant if they display any symptoms of the hereditary cancers linked to a BRCA mutation.

If you have a family history including anything listed below, book an appointment with your GP to discuss it.  It is useful to take any details you have with you so that you can show a pattern of cancers within your family.  Ask your GP to refer you to your local genetics centre where you can further discuss your family history and concerns with a specialist genetic counsellor.

Features that indicate increased likelihood of carrying a BRCA mutation

There are a number of features and / or risk factors which could indicate that you may carry a BRCA gene mutation or are more likely to carry a BRCA gene mutation compared to the general population. These include – but are not limited to:

  • Multiple cases of breast cancer within a family
  • Pre-menopausal breast cancer
  • Ovarian cancer (fallopian tube, primary peritoneal)
  • Breast and ovarian cancer on one side of family
  • Bilateral breast cancer
  • Male breast cancer
  • Triple negative breast cancer (ER-/PR-/Her2-)
  • Pancreatic cancer
  • Aggressive prostate cancer
  • Ashkenazi Jewish ancestry