A dot in ALT

[Cheng Grace]

Hello expert,
I have used Strelka version 1.0.15 to call SNPs of my exome data.

In the output vcf file, I found that the some of the SNPs called has a dot in the ALT column. Below is the some the example rows (the problematic rows is highlighted in red):

#CHROM	POS	ID	REF	ALT	QUAL	FILTER	INFO	FORMAT	NORMAL	TUMOR
chr1	1211398	.	G	T	.	QSS_ref	NT=ref;QSS=7;QSS_NT=7;SGT=GG->GT;SOMATIC;TQSS=1;TQSS_NT=1	DP:FDP:SDP:SUBDP:AU:CU:GU:TU	21:0:0:0:0,0:0,0:21,21:0,0	18:0:0:0:0,0:0,0:15,15:3,3
chr1	1722625	.	A	.	.	QSS_ref	NT=ref;QSS=2;QSS_NT=2;SGT=AA->AA;SOMATIC;TQSS=1;TQSS_NT=1	DP:FDP:SDP:SUBDP:AU:CU:GU:TU	15:0:0:0:15,15:0,0:0,0:0,0	18:0:0:0:15,15:0,0:0,0:3,4
chr1	12793892	.	T	C	.	QSS_ref	NT=ref;QSS=2;QSS_NT=2;SGT=CT->CT;SOMATIC;TQSS=1;TQSS_NT=1	DP:FDP:SDP:SUBDP:AU:CU:GU:TU	37:1:0:0:1,2:1,2:0,0:34,37	47:0:0:0:0,0:5,11:0,0:42,43
chr1	12861165	.	C	T	.	QSS_ref	NT=ref;QSS=5;QSS_NT=5;SGT=CC->CT;SOMATIC;TQSS=2;TQSS_NT=2	DP:FDP:SDP:SUBDP:AU:CU:GU:TU	91:0:0:0:0,0:90,114:0,0:1,2	93:0:0:0:0,0:84,116:0,0:9,12
chr1	12882578	.	G	.	.	QSS_ref	NT=ref;QSS=1;QSS_NT=1;SGT=GG->GG;SOMATIC;TQSS=1;TQSS_NT=1	DP:FDP:SDP:SUBDP:AU:CU:GU:TU	26:0:0:0:0,0:0,0:26,26:0,0	31:1:0:0:4,11:0,0:25,26:1,1

May I know that is it normal to have a dot in the ALT column? If yes, what's the meaning of a dot for the ALT allele?

Thanks for your help!

Cheers,
Grace