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Variant Discovery in High-Throughput Sequencing Data

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Developed in the Data Sciences Platform at the Broad Institute, the toolkit offers a wide variety of tools with a primary focus on variant discovery and genotyping. Its powerful processing engine and high-performance computing features make it capable of taking on projects of any size. Learn more

Long deletion split into two deletions nearby an SNV.

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    Gökalp Çelik

    Hi Seungho Oh

    This is due to how that region costs less to realigner compared to marking one long indel and one mismatch. Mismatch in this case might have caused more penalty to be assigned to the realigner therefore a split gap is preferred by the reassembly and realigner engine. Both HaplotypeCaller and Mutect2 have Partially Determined HMM support for resolving such cases a little more carefully however the current implementation is slower and may not be fully ready for production use. 

    What PDHMM does is, it takes raw pileup calls from a given active region and inserts them into assembly graphs generated by HaplotypeCaller/Mutect2 to test the viability of those haplotypes for a proper call. This process is performed for every single assembled haplotype therefore it takes longer to complete a single run. Current valid implementation is Java based and there are still issues with it. There will be a native AVX accelerated version available soon once all the issues are resolved. 

    What you can do to test if that works for your case is add the below parameters to Mutect2 and observe changes

    --pileup-detection true \
    --pileup-detection-enable-indel-pileup-calling true \
    --pileup-detection-absolute-alt-depth 0 \
    --pileup-detection-bad-read-tolerance 0.40 \
    --pileup-detection-active-region-phred-threshold 3.0 \
    --pileup-detection-filter-assembly-alt-bad-read-tolerance 0.4 \
    --use-pdhmm true

    Some of these parameters are still hidden and not evident in the help text. These parameters are part of the DRAGEN Functional Equivalence parameters. 

    Let us know how it goes. 

    Regards. 

     

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