Detecting cancer gene mutations from home: What you need to know

By Allison MacAlister
CCSN Communications & Social Media Coordinator

On March 6th 2018, the DNA test company 23andMe announced that it now has approval to tell customers of their mail-in DNA-testing kit about three gene mutations of BRCA1 and BRCA2 as part of their genetic health results.

What does that mean, and is it worth being concerned about? Let’s talk about the facts.

Gene mutations? BRCA?

In the simplest of lay terms, gene mutations can sometimes occur when your DNA makes an error in replicating your genetic code to new cells. Since cells divide millions of times a day, errors happen quite often and are usually caught by a gene’s repair proteins before any issues arise.

However, when the DNA repair proteins can’t fix the problem, gene mutations occur.

DNA Strand Breaking
(image from jezebel.com)

The BRCA1 and BRCA2 genes produce tumour-suppressor proteins. If they are mutated, their repairs will “glitch” much more often than average – enough to potentially hit a critical mass of tumour-promoting mutations within a cell. This makes a woman with a BRCA1 or BRCA2 gene mutation much more likely to develop breast cancer, with associated higher risks for ovarian cancer as well.  The general population breast cancer risk is 12%. BRCA mutations raise that stat to up to a staggering 69% for BRCA2 and 72% for BRCA1.[1]  In men with a BRCA mutation, risk for male breast cancer and prostate cancer rise.

What is 23andMe?

23andMe Logo

23andMe is a home-based DNA collection kit that allows individuals to mail a saliva sample to their labs, and receive detailed results about their DNA in the mail several weeks later. The name “23andMe” is in reference to the fact that human DNA has 23 pairs of chromosomes.

23andMe currently offers two kits:

  • Ancestry, which offers ancestry reports from 150+ regions and an opt-in DNA relative finder.
  • Ancestry + Health, which offers the Ancestry report plus detailed results on health risks, carrier statuses, wellness reports and physical trait reports.

The BRCA mutation testing would be available exclusively through the Ancestry + Health kit, along with many other approved health tests. Though the recent approval is significant news, they are no strangers to acquiring FDA approval for their take-home tests – they already offer over 40 reports for various gene mutations and inherited conditions, including cystic fibrosis, sickle cell anemia and others.[2]

In every carrier status report they offer, 23andMe clarify that they only test for certain variants of gene mutations – the test subject could still have a variant not covered by the 23andMe test. In the case of the BRCA gene mutations, 23andMe can only detect three of over a thousand known inherited BRCA1 and BRCA2 mutations, and the three in question are not even the most common. It is unable to determine a person’s overall risk of cancer using these results alone.

Is it worth using 23andMe to test for BRCA and other carrier risk?

DNA tests have improved vastly over the years, and can be a useful tool for looking at genetic markers for health risks – especially for individuals who have been adopted, or estranged from their biological family. Many people in the US, Canada and worldwide have used 23andMe in recent years.

Most physicians would recommend taking the results of these tests with a large grain of salt. It’s worth repeating that the test only covers three of thousands of BRCA gene mutations that could cause breast cancer, and the chance of an individual having a BRCA1/2 mutation is less than one percent overall. On top of this, false positives in DNA tests are common, and testing positive for BRCA or any other genetic risk factors within the test isn’t necessarily accurate.

Woman looking at her laptop, concerned
(stock image)

In this modern age of medicine, practitioners and patients alike tend to seek out as much information as we can – patients deserve to know as much as they can about their own health, after all! However, there’s something to be said about some ignorance. You can’t undo the knowledge that you have a high risk of developing breast cancer, let alone the other potential positives in a 23andMe test.

What if I think I may have a BRCA gene mutation?

Do any of the following scenarios apply to you?

  • A family member was identified as a carrier of BRCA1or BRCA2
  • You are an Ashkenazi Jewish woman with a first or second-degree relative diagnosed with breast  or ovarian cancer, or male breast cancer.
  • Your family history is strongly suggestive of hereditary breast/ovarian cancer – e.g. two or more relatives on the same family side affected with early onset breast cancer or ovarian cancer (i.e. occurring earlier than considered normal).

If so, you are at a higher risk than average for a BRCA mutation, and government-sponsored genetic testing in Canada may be available to you.

A woman speaking with her doctor
(stock image)

If the above does not apply to you but you have a family history of breast or ovarian cancer, you can request a referral for genetic counselling from your family practitioner. A genetic counsellor will assess your family history and help you determine whether you qualify for genetic testing. [3]

You can learn more about genetic counselling and genetic testing in your province here.

Conclusion

If you really want to know your genetic risk factors for illnesses, 23andMe provides a lot of information as a baseline for you to draw from – but sometimes it can be too much or too little. In the case of potential concerns resulting from your test or concerns about gene mutations in general, a visit to your general practitioner is the right course of action before all else.


[1] https://www.cancer.gov/about-cancer/causes-prevention/genetics/brca-fact-sheet

[2] https://www.23andme.com/dna-reports-list/

[3] https://www.geneyouin.ca/where-to-get-genetic-testing-for-breast-cancer-in-canada/

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