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CNVkit- weird results when using the same sample as normal

Hi, I'm using CNVkit to detect copy number alterations in hybridized capture panel. When I've used the same sample (exactly the same bam) as a reference I somehow do find some CNA. We used the batch command followed by the call command with default parameters (and with dropping low-coverage). 15 out of the 75 segments were found to have copy-number alteration (cn!=2). The cnn files are exactly the same both for the on- and off-targets so the problem starts when creating the cnr. Any idea why this discrepancy happens?

cnv

1 answer

Sorry, I'm not sure I follow. Could you paste both commands here so I can see the difference?

Thanks for your reply, I'll clarify. There are no two commands, just a batch command of the same sample as test and normal sample:

cnvkit.py batch SAMPLE.bam -n SAMPLE.bam --targets TAR.bed --annotate refFlat.txt --fasta ~ucsc.hg19.fasta --access access-5k-mappable.hg19.bed --output-reference ref.cnn --output-dir --drop-low-coverage

and then: cnvkit.py call SAMPLE.cns

This is expected. CNVkit doesn't directly subtract the normal from the test sample; the normal sample is one of several factors that go into the final calls.

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