Sunday, August 4, 2019

Please Take Time to Critically Assess Anxiety-Inducing Results

I am reproducing part of the content from the FamilyTreeDNA GitHub section here:

I received a result that caused me some anxiety for a couple hours (even though I realized it rationally couldn't be true).

Namely, you can upload your 23andMe data to search the database of FamilyTreeDNA members (or other people who have uploaded data).  I was told that there was someone within the range of "Father/Son", who was also an X-chromosome match (and "X-match").  This is not possible: I am a male, so a father or son would have to have a Y-chromosome match (and not an X-chromosome match).

I e-mailed the contact (you can see the e-mail address for your predicted relatives), but I never heard back.  One possibility is that someone could have created a false account that was based upon my public genome data, but I don't know that for certain.  For example, there are a lot of people listed within the range of "2nd Cousin - 4th Cousin," and I don't recognize any of them.  I also don't have access to the raw data for this individual.  In other words, all I know is that this result can't be precise.

For example, as of 10/3/2019, it looks like other people have encountered a similar result with a self-search (so, it may be the "Father/Son" part is not precise, and instead should have said "Self/Twin").  If that is the case, you can see that explanation on Twitter here.  FamilyTreeDNA also confirmed that kits from the same individual (or monozygotic twins) will also appear as "Parent/Child" with 50% similarity, as described in this table.

More importantly, as a general rule, if you encounter a surprising result, I would like to encourage people to first pause and then try to calm down and critically assess the results.  This can go both ways - for example, I would also recommend waiting at least one day before posting anything negative (as probably would have been wise for a Food Sensitivity test, although I have posted an apology in that section).

To be clear, I would usually expect an IBD calculation for the same individual or parent-child relationship to be reliable.  For example, you can see a clear difference when comparing my own samples versus 1000 Genomes samples and most parent-to-child relationships on this blog post (please scroll towards the bottom of the page).  I have also found known and validated novel relationships on 23andMe and AncestryDNA.

Unfortunately, unexpected family relationships can sometimes be true.  However, there can also be limits to the precision of genomics methods and possibly even some allowance for human error (such as sample mix-ups).  So, please take some time to think about making decisions that could affect the rest of your life and may permanently affect your relationships.  For example, to troubleshoot a possible sample swap, do all people involved have predicted relationships with other people fitting the alternative model?  If one person has expected relatives and the other person doesn't have any matches that can be explained, perhaps that indicates the sample that should be re-processed (either with the same company, and/or a different company).

In other words, if you encounter a result that causes you anxiety, please first try to calm down.  Then, please take some time to evaluate the situation: the result could be real, but please also ask questions (from independent resources) about whether there could be misunderstanding and/or inaccurate information that has caused you concern.  For the potential misunderstanding part, perhaps a good first step would be to contact technical support and/or a genetic counselor.

Update Log:

8/4/2019 - public post date
8/6/2019 - minor changes
8/15/2019 - minor changes
10/3/2019 - add solution suggested from Twitter
10/7/2019 - add link from FamilyTreeDNA
7/22/2020 - add link to discussion about uploaded data
6/21/2024 - fix minor typos


  1. The full match on the X chromosome is an artifact of the way FTDNA identifies matching segments. It looks for contradictions to a match, opposite homozygotes. For instance if one party has AA for a SNP and the other party has GG, the result cannot come from a common ancestor.

    Some people upload experimental kits that lack X data (for instance, a file with imputed data). FTDNA does not detect a contradiction to the match because there is no data. They could easily change their algorithm, but they have not done so to date.

    1. Thank you for the input - FTDNA didn't provide me the sample that was uploaded from the other user, but they essentially said it was a match for my data (100%, not 50%). They said that I could submit something in writing if I wanted that account deleted. However, unless there is strong concern from other family members, I am OK with leaving that account as an example (and keeping the ability to warn other individual users). If the file was uploaded under a more realistic name, I think that would be a bigger problem.

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