vcf2maf

To convert a VCF into a MAF, each variant must be mapped to only one of all possible gene transcripts/isoforms that it might affect. This selection of a single effect per variant, is often subjective. So this project is an attempt to make the selection criteria smarter, reproducible, and more configurable. And the default criteria must lean towards best practices.

Quick start

Download the latest stable branch of vcf2maf, and view the detailed usage manual:

curl -LO https://github.com/mskcc/vcf2maf/archive/master.zip; unzip master.zip; cd vcf2maf-master
perl vcf2maf.pl --man

To download properly versioned releases, click here for a list.

If you don't have VEP installed, see the sections below. VEP is preferred for it's CLIA-compliant HGVS formats, and is used by default. So after installing VEP, you can test the script like so:

perl vcf2maf.pl --input-vcf data/test.vcf --output-maf data/test.maf

To fill columns 16 and 17 of the output MAF with tumor/normal sample IDs, and to parse out genotypes and allele counts from matched genotype columns in the VCF, use options --tumor-id and --normal-id. Skip option --normal-id if you didn't have a matched normal:

perl vcf2maf.pl --input-vcf data/test.vcf --output-maf data/test.maf --tumor-id WD1309 --normal-id NB1308

VCFs from variant callers like VarScan use hardcoded sample IDs TUMOR/NORMAL in the genotype columns of the VCF. To have this script correctly parse the correct genotype columns, while still printing the proper IDs in the output MAF:

perl vcf2maf.pl --input-vcf data/test_varscan.vcf --output-maf data/test_varscan.maf --tumor-id WD1309 --normal-id NB1308 --vcf-tumor-id TUMOR --vcf-normal-id NORMAL

If you have VEP in a different folder like /opt/vep, and cached in /srv/vep, there are options available to point the script there:

perl vcf2maf.pl --input-vcf data/test.vcf --output-maf data/test.maf --vep-path /opt/vep --vep-data /srv/vep

maf2maf

If you have a MAF or a MAF-like file that you want to reannotate, then use maf2maf, which simply runs maf2vcf followed by vcf2maf:

perl maf2maf.pl --input-maf data/test.maf --output-maf data/test.vep.maf

After tests on variant lists from many sources, maf2vcf and maf2maf are quite good at dealing with formatting errors or "MAF-like" files. The bare minimum columns that it expects as input are:

Chromosome	Start_Position	Reference_Allele	Tumor_Seq_Allele2	Tumor_Sample_Barcode
1	3599659	C	T	TCGA-A1-A0SF-01
1	6676836	A	C	TCGA-A1-A0SF-01
1	7886690	G	A	TCGA-A1-A0SI-01

See data/minimalist_test_maf.tsv for a sampler. Addition of Tumor_Seq_Allele1 will be used to determine zygosity. Otherwise, it will try to determine zygosity from variant allele fractions, assuming that arguments --tum-vad-col and --tum-depth-col are set correctly to the names of columns containing those read counts. Specifying the Matched_Norm_Sample_Barcode with its respective columns containing read-counts, is also strongly recommended.

Install VEP

Ensembl's VEP (Variant Effect Predictor) is popular for how it picks a single effect per gene as detailed here, its CLIA-compliant HGVS variant format, and Sequence Ontology nomenclature for variant effects.

To follow these instructions, we'll assume you have these packaged essentials installed:

sudo yum install -y curl rsync tar make perl perl-core
## OR ##
sudo apt-get install -y curl rsync tar make perl perl-base

You'll also need samtools and tabix in your $PATH, which can be found at htslib.org

Set PERL_PATH to where you want to install additional perl libraries. Change this as needed:

export PERL_PATH=~/perl5

Handle VEP's Perl dependencies using cpanminus to install them under $PERL_PATH:

curl -L http://cpanmin.us | perl - --notest -l $PERL_PATH LWP::Simple LWP::Protocol::https Archive::Extract Archive::Tar Archive::Zip CGI DBI Time::HiRes

Set PERL5LIB to find those libraries. Add this to the end of your ~/.bashrc to make it persistent:

export PERL5LIB=$PERL_PATH/lib/perl5:$PERL_PATH/lib/perl5/x86_64-linux

Create temporary shell variables pointing to where we'll store VEP and its cache data (non default paths can be used, but specify --vep-path and --vep-data when running vcf2maf oe maf2maf):

export VEP_PATH=~/vep
export VEP_DATA=~/.vep

Download the v82 release of VEP:

mkdir $VEP_PATH $VEP_DATA; cd $VEP_PATH
curl -LO https://github.com/Ensembl/ensembl-tools/archive/release/82.tar.gz
tar -zxf 82.tar.gz --starting-file variant_effect_predictor --transform='s|.*/|./|g'

Add that path to PERL5LIB, and the htslib subfolder to PATH where tabix will be installed:

export PERL5LIB=$VEP_PATH:$PERL5LIB
export PATH=$VEP_PATH/htslib:$PATH

Download and unpack VEP's offline cache for GRCh37, GRCh38, and GRCm38:

rsync -zvh rsync://ftp.ensembl.org/ensembl/pub/release-82/variation/VEP/homo_sapiens_vep_82_GRCh{37,38}.tar.gz $VEP_DATA
rsync -zvh rsync://ftp.ensembl.org/ensembl/pub/release-82/variation/VEP/mus_musculus_vep_82_GRCm38.tar.gz $VEP_DATA
cat $VEP_DATA/*_vep_82_GRC{h37,h38,m38}.tar.gz | tar -izxf - -C $VEP_DATA

Install the Ensembl API, the reference FASTAs for GRCh37/GRCh38/GRCm38, and some neat VEP plugins:

perl INSTALL.pl --AUTO afp --SPECIES homo_sapiens,mus_musculus --ASSEMBLY GRCh38,GRCm38 --PLUGINS CADD,ExAC,dbNSFP,UpDownDistance --DESTDIR $VEP_PATH --CACHEDIR $VEP_DATA
perl INSTALL.pl --AUTO afp --SPECIES homo_sapiens --ASSEMBLY GRCh37 --PLUGINS CADD,ExAC,dbNSFP,UpDownDistance --DESTDIR $VEP_PATH --CACHEDIR $VEP_DATA

Convert the offline cache for use with tabix, that significantly speeds up the lookup of known variants:

perl convert_cache.pl --species homo_sapiens,mus_musculus --version 82_GRCh37,82_GRCh38,82_GRCm38 --dir $VEP_DATA

Download and index a custom ExAC r0.3 VCF, that skips variants overlapping known somatic hotspots:

curl -L https://googledrive.com/host/0B6o74flPT8FAYnBJTk9aTF9WVnM > $VEP_DATA/ExAC.r0.3.sites.minus_somatic.vcf.gz
tabix -p vcf $VEP_DATA/ExAC.r0.3.sites.minus_somatic.vcf.gz

Test running VEP in offline mode with the ExAC plugin, on the provided sample GRCh37 VCF:

perl variant_effect_predictor.pl --species homo_sapiens --assembly GRCh37 --offline --no_progress --everything --shift_hgvs 1 --check_existing --check_alleles --total_length --allele_number --no_escape --xref_refseq --dir $VEP_DATA --fasta $VEP_DATA/homo_sapiens/82_GRCh37/Homo_sapiens.GRCh37.75.dna.primary_assembly.fa --plugin ExAC,$VEP_DATA/ExAC.r0.3.sites.minus_somatic.vcf.gz --input_file example_GRCh37.vcf --output_file example_GRCh37.vep.txt

Authors

Cyriac Kandoth (ckandoth@gmail.com)

License