The 23andMe BRCA test

In case you were sleeping under a rock, 23andMe got FDA approval for DTC testing of markers related to BRCA risk. Obviously, this is a pretty big step, in principle.

But the short-term implications are not that earth-shaking.

From the FDA release:

The three BRCA1/BRCA2 hereditary mutations detected by the test are present in about 2 percent of Ashkenazi Jewish women, according to a National Cancer Institute study, but rarely occur (0 percent to 0.1 percent) in other ethnic populations. All individuals, whether they are of Ashkenazi Jewish descent or not, may have other mutations in BRCA1 or BRCA2 genes, or other cancer-related gene mutations that are not detected by this test. For this reason, a negative test result could still mean that a person has an increased risk of cancer due to gene mutations….

Apparently, women with one of these variants have a 45-85% chance of developing breast cancer by age 70. So the penetrance is high.

It seems that you’ll know if this sort of test is going to have utility for you based on family history.

The big thing is the transition to DTC. This will increase availability and drive the price down. That’s probably going to mean more work for those engaged in interpretation and education. False positives are going to start being a major thing….

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7 thoughts on “The 23andMe BRCA test

  1. You are quite right about false positives. Bad testing is a major driver of medical costs…I’m sure you know this. Anyway, do you have any rate-of-error data for genome work?

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  2. re: cost of testing, in the near future re: genomics, everyone in the developed world will have a very high quality sequence with long enough reads to detect structural variants. that is, aside from speciality cases, such as somatic mutations in cancer or localized issues, for genetics you may get tested once.

    the problem is ppl not understanding base rate fallacy. i think we need better automated analytics.

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  3. “It seems that you’ll know if this sort of test is going to have utility for you based on family history.”-
    In their press release, they say that they found, consistently with the prior studies, that about half of the identified carriers had no history of cancer in the first degree relatives. It isn’t too surprising, since penetrance is high but not not too high, families are small so few carriers have sisters with the same mutations, and half of women inherit it from the fathers who can be asymptomatic? This is their target people, the ones without strong family history. And conversely, for people with strong Hx, insurers already cover the established, more comprehensive tests (not just for these 3 ethnic mutations, but for thousands more … it’s a long loss of function gene where any number of novel truncating mutations are discovered daily)

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  4. Mary Claire-King, amongst others, has criticized the 23andme BRCA test as very incomplete – genotyping three SNPs but leaving out the long tail of potentially harmful mutations that could be detected by sequencing.

    https://www.genomeweb.com/molecular-diagnostics/oncology-community-sees-potential-patient-harm-fda-ok-23andme-brca-test

    Are DTC consumers capable of understanding these nuances, or will a false sense of security lead to potentially tragic consequences for BRCA1 positive individuals who do not carry risk alleles at any of the 3 typed SNPs?

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  5. The province of Ontario had a free screening program several years ago. A friend turned up positive for BRCA2 (her mother had died of breast cancer) and elected to have a prophylactic double mastectomy.

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