Saturday, November 11, 2017

Discrepancies with Amount of Shared DNA for Close Family Matches at MyHeritage

I was previously aware that there are some issues with the more distant matches on MyHeritage DNA, so I have been advising caution about using those in genealogical research, but was more confident about the close family matches. I uploaded both my parents' data and my aunt and uncle and all matched me and each other as expected. However, in the last couple of days, I have become aware of some pretty serious issues with matches in the category that includes half-sibling relationships (~25% shared).

Case #1
For several months, I have been working with a woman who was abandoned as a baby. We had successfully zeroed in on her biological family through pedigree triangulation on AncestryDNA and were trying to determine which of two sisters was her biological mother. The daughter of one of the sisters had agreed to test at MyHeritage, with the expectation of a DNA share consistent with either first cousins or half-siblings. Her results came back with 17.9% (1,294.9 cM) DNA shared between them. This was unfortunate since it fell in a gray area where the ranges of shared DNA for the two possible relationships overlap, so it looked like we would have no definitive answer to the question of her parentage. We then uploaded her data to Gedmatch and were shocked to see that they actually shared ~25% (1,758.9 cM) of their DNA - a clear half-sibling match.

This is what the comparison on MyHeritage looked like:


This is what the comparison looked like on Gedmatch:

That is a 464 cM difference! This pushes the relationship solidly into the half-sibling relationship category without any ambiguity. We expect small differences between the different companies and/or third party comparisons, but in all the years I have been involved in genetic genealogy, I have never seen a comparison vary so drastically. In fact, they have been so consistent in the eight years we have been working with autosomal DNA matching, that it has given our community great confidence about the reliability of the matching algorithms that we work with at the three major DNA companies and Gedmatch. 

This was very concerning to me so I followed up on some potentially similar situations I had heard about in my DNA Detectives Facebook group and immediately found two more examples like the one above.

Case #2
Here is the comparison between two half-siblings at MyHeritage:



Here they are at AncestryDNA:




And here they are at Gedmatch:




As you can see, this set of half-sisters was reported to share 1,142 cM at MyHeritage, 1,620 cM at AncestryDNA and 1,699.4 cM at Gedmatch.  Again, this is highly problematic with a difference of 478 cM and 557 cM between MyHeritage's estimate and the other two services.


Case #3
This is a comparison of a full uncle/nephew at MyHeritage:

and at Gedmatch:

Again, we see a large discrepancy between the comparison at MyHeritage versus the one at Gedmatch - 937 cM at the former versus 1,409.2 cM at the latter, for a difference of 472.2 cM.  Also note, that the number of matching segments is doubled in the Gedmatch comparison as opposed to the MyHeritage one.

I would really like to see the MyHeritage comparisons on a chromosome browser to determine exactly what is going on here. Hopefully, they will soon add that feature.

Don't get me wrong, I welcome new companies that offer services to our community and am very supportive of their efforts, however accuracy is absolutely essential when using DNA to draw genealogical conclusions and determine the relationship between two people. These very significant discrepancies definitely can and, perhaps, already have caused MyHeritage customers to reach inaccurate conclusions about their relationships to each other. This can be very damaging to the reputation of our industry and, especially, in relation to the work I do assisting people of unknown parentage to identify and connect with their biological families. If we cannot count on reliability in the reported amount of shared DNA, this undermines our efforts to convince newly-found family members that the proposed relationship is authentic. It is my hope that MyHeritage will move quickly to correct this very serious issue. In the meantime, I recommend always double checking your comparisons by uploading to Gedmatch and running the one-to-one comparison there. 

I was able to locate these examples very quickly, so I am confident there are many more out there. Please comment below if you have an example of your own.

[Edited to add - I am still recommending that people of unknown parentage get their DNA into the MyHeritage database due to the many success stories we are seeing there, but I strongly suggest checking any important/significant matches at Gedmatch, if at all possible, to confirm any newly-found relationships.]