Dear samtools community,

I have a 10bp deletion called with DP=42 and DP4=0,6,0,16 and IDV=8. There is 
no second variant 
allele called at this site.

Looking at the alignment manually, I see exactly 8 reads showing the deletion. 
This is consistent 
with IDV=8.

And I see a total of 42 reads (including the 8 deletion reads) spanning the 
position, which is 
consistent with DP=42.

I have checked both base- and mapping qualities (e.g. samtools depth -q 15 -Q 
15 also gives 42) and 
they seem not responsible for the DP4 calls. And I cannot understand how the 
third and fourth 
position of DP4 (0,16) can be larger than IDV (8). I hope someone can explain 
this to me.

And if 42 reads/bases are of high quality, how can the sum over DP4 be so small 
(22)?


I am using samtools 1.3.1 and bcftools 1.3.1 (but have seen the same issue with 
samtools 0.1.18 as 
well). The commandlines were

samtools mpileup -u -q 15 -f hg19.fa -m 3 -F 0.03 -B -d 10000000 -L 10000000 -l 
<(echo -e 
"chr1\t237955648\t237955649") case.bam | bcftools call -c -

This is the VCF result (excluding headers):

chr1    237955649       .       C       .       155.995 .       
DP=42;MQSB=1;MQ0F=0;AF1=0;AC1=0;DP4=3,39,0,0;MQ=60;FQ=-152.987GT:PL     0/0:0
chr1    237955649       .       
CTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGTGCGTGTGTGTGTGTGTGCGTGTGTGTGTGTGTGTGTGTGTGTGT 
CTGTGTGTGTGTGTGTGTGTGTGCGTGTGTGTGTGTGTGCGTGTGTGTGTGTGTGTGTGTGTGTGT      217.469 
. 
INDEL;IDV=8;IMF=0.190476;DP=42;VDB=7.68124e-06;SGB=-0.689466;MQ0F=0;AF1=0.50002;AC1=1;DP4=0,6,0,16;MQ=60;FQ=7.35744;PV4=1,1,1,0.276636
 
GT:PL   0/1:255,0,41


Best regards,
Florian Battke


-- 
Dr. Florian Battke

Associate Director Bioinformatics & IT

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