Improve docs for extract_snps.py about hisat2

[roryk]

Hi @JPFinnigan,

This could be happening because your mm10.fa and GTF file do not match in the chromosome names. Can you check that they match?

[JPFinnigan]

Hello,

The FASTA file and the snp_file have the same naming convention for chromosomes (chr_). I think this problem may stem from the fact that my snp_file is a .vcf. I was looking through the some other posted issues and it seems as though its not yet possible to pass a .vcf to extract_snps.py. But perhaps this is not the case?

Either way I wanted to explain myself. I'm sure this has come up in your internal discussions, but we're excited about the potential of using HISAT2 to support alignment against custom reference-graphs created from SNV/INDEL call-sets derived from joint mutation calling from tumor-normal pairs. (e.g a graph reference containing the reference allele, plus germline SNP/INDEL, plus somatic SNP/INDEL). We (cc: @iskandr) would be eager to hear your thoughts.

[roryk]

Hi @JPFinnigan,

There isn't a script to do it from a VCF file, but I think it wouldn't be too hard to write one. I think you'd have to decompose multiallelic variants and normalize them so they are all left shifted first. You can do both of those operations with vt decompose and vt normalize (http://genome.sph.umich.edu/wiki/Vt) @infphilo, if we did that and called SNP/indel/deletion via just looking at length differences between ref and alt, would that be enough?

[infphilo]

HISAT2 now supports VCF file - see the HISAT2 webpage. I will update the usage information to make clear which files and formats are used.