Strand Bias filtering

[c_ro87]

Hello all,
i run the variantCaller in germline_low_stringency mode with the default parameters

the strand bias threshold for snp Strand Bias is 0.95, everything up that value is considered strand bias

we did some calculations using Relative Strand Bias Formula

http://mendel.iontorrent.com/ion-docs/attachments/15007750/31621166.jpg

We found some cases where this filter works bad, for instance when we have FSAF:2 FSAR:1 FSRR:10 FSRF:0, the STB is 0.916 and therefore accepted as variant. Or FSAF:1 FSAR:1 FSRR:20 FSRF:20 the STB is 0.5 and therefore accepted again. So... we accept that calls???

[arnaud83]

Hello all,
i run the variantCaller in germline_low_stringency mode with the default parameters

the strand bias threshold for snp Strand Bias is 0.95, everything up that value is considered strand bias

we did some calculations using Relative Strand Bias Formula

http://mendel.iontorrent.com/ion-docs/attachments/15007750/31621166.jpg

We found some cases where this filter works bad, for instance when we have FSAF:2 FSAR:1 FSRR:10 FSRF:0, the STB is 0.916 and therefore accepted as variant. Or FSAF:1 FSAR:1 FSRR:20 FSRF:20 the STB is 0.5 and therefore accepted again. So... we accept that calls???

Strand bias is not the only parameter to take into account to remove false positive. Alternate allele frequency, Alternate allele count, Mapping quality, position on the read can be very usefull to filter variants.

[IonTom]

For Amplicon data a strand bias seems to be much more frequent than for Exome sequencing. So maybe filters should not be quite as strict. Maybe it is enough to check if a
variant is found on both strands, or at least one percent on each strand. On the other hand
i analyzed one sample where there was a significant bias for amplicon data and the strand bias was also found on exome data for the same sample.

The Mutascope publication (specifically the supplement) discusses the Amplicon strand bias problem in more detail: http://bioinformatics.oxfordjournals...rmatics.btt305