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Bug in HaplotypeCaller: GT is called 0/1, but AD is 206,0
HI, I'd like to report a weird result from HaplotypeCaller.
We have a patient sequenced by targeted sequencing on HNF1B. This patient has been confirmed to have a whole gene deletion of HNF1B so we used this patient as a positive control. We expected to see no heterozygous variants called in HNF1B.
However, HaplotypeCaller called two heterozygous variants: one deletion (it didn't pass the FS strand bias filter and the ReadPosRankSumTest filter) and one substitution (this one passed all the quality filters). Both these two variants were not called by UnifiedGenotyper (and the variants called by UnifiedGenotyper in HNF1B region were all homozygous as what we expected)
Please see the VCF table:
There are three things I want to highlight:
1, The deletion is only 10 bases upstream of the substitution, but the FS score is enormous for the deletion whereas very low for the substitution. If there's a strand bias, it must affect both variants if they are so close to each other.
2, The score of ReadPosRankSumTest of the deletion didn't pass the filter because it's always called near the end of the reads. The ReadPosRankSumTest score for the substitution is missing.
3, The genotype was called 0/1 for the substitution, but if we look at the AD, there are 206 reads supporting the ref allele and 0 read supporting the alt allele. Going by the AD, it's clearly a homozygous ref/ref genotype.
Then I looked into the bam files. It turns out the all the alternative alleles of the substitution were from the ends of bad reads, and there are not too many of them after all. So the reads in the bam file also support a homozygous ref/ref genotype.
Therefore I'm really confused why the substitution has 0/1 genotype called by the HaplotypeCaller and why it passed the filter.