I'm reading a preprint on a new somatic variant discovery tool, and the first sentence of the Discussion section has me confused.

Across the four datasets analyzed in this study, we discovered that the major source of disagreement between callers originates from somatic variants called within STRs, in particular if the motif is two base pairs or longer.

The "two base pairs or longer" bit is what confuses me. I interpreted "motif" as referring to the short tandem repeats (STRs), which are by definition 2 bp or longer. A motif of < 2 bp is...a homopolymer, not really a motif in the common sense.

Am I missing something here? Or is this simply an awkward word choice on the part of the authors?

  • $\begingroup$ I doubt you’re missing anything, I suspect they’re using confused wording. $\endgroup$
    – Devon Ryan
    Commented Nov 8, 2017 at 21:15

1 Answer 1


What's your reference for the definition of STRs? I think it is still ambiguous among the community. Wikipedia states motifs of >=2 bp. However other references include homopolymers as well:
Source 1, source 2 and source 3.


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