EnsemblEnsembl Home

Variant Effect Predictor Custom annotations


VEP can integrate custom annotation from standard format files into your results by using the --custom flag.

These files may be hosted locally or remotely, with no limit to the number or size of the files. The files must be indexed using the tabix utility (BED, GFF, GTF, VCF); bigWig files contain their own indices.

Annotations typically appear as key=value pairs in the Extra column of the VEP output; they will also appear in the INFO column if using VCF format output. The value for a particular annotation is defined as the identifier for each feature; if not available, an identifier derived from the coordinates of the annotation is used. Annotations will appear in each line of output for the variant where multiple lines exist.

Data formats

VEP supports the following formats:

  • Gene/transcript annotations. Requires FASTA file; see documentation.
    • GFF : a format for describing genes and other genomic features.
    • GTF : a similar format derived from GFF.
  • Variant data
    • VCF : a format used to describe genomic variants. VEP will use the 3rd column of the file as the identifier. INFO fields from records may be added to the VEP output.
  • Basic/uninterpreted data
    • BED : a simple tab-delimited format containing 3-12 columns of data. The first 3 columns contain the coordinates of the feature. If available, VEP will use the 4th column of the file as the identifier of the feature.
    • bigWig : a format for storage of dense continuous data. VEP uses the value for the given position as the "identifier". Note that bigWig files contain their own indices, and do not need to be indexed by tabix. Requires Bio::DB::BigFile.

Any other files can be easily converted to be compatible with VEP; the easiest format to produce is a BED-like file containing coordinates and an (optional) identifier:

chr1    10000    11000    Feature1
chr3    25000    26000    Feature2
chrX    99000    99001    Feature3

Chromosomes can be denoted by either e.g. "chr7" or "7", "chrX" or "X".


Preparing files

Custom annotation files must be prepared in a particular way in order to work with tabix and therefore with VEP. Files must be stripped of comment lines, sorted in chromosome and position order, compressed using bgzip and finally indexed using tabix. Here is an example of that process for a GFF file:

grep -v "#" myData.gff | sort -k1,1 -k2,2n -k3,3n -t$'\t' | bgzip -c > myData.gff.gz
tabix -p gff myData.gff.gz

The tabix utility has several preset filetypes that it can process, and it can also process any arbitrary filetype containing at least a chromosome and position column. See the documentation for details.

If you are going to use the file remotely (i.e. over HTTP or FTP protocol), you should ensure the file is world-readable on your server.


Options

Each custom file that you configure VEP to use can be configured. Beyond the filepath, there are further options, each of which is specified in a comma-separated list, for example:

./vep -custom frequencies.bw,Frequency,bigwig,exact,0
./vep -custom http://www.myserver.com/data/myPhenotypes.bed.gz,Phenotype,bed,exact,1

The options are as follows:

  • Filename : The path to the file. For tabix indexed files, the VEP will check that both the file and the corresponding .tbi file exist. For remote files, VEP will check that the tabix index is accessible on startup.
  • Short name : A name for the annotation that will appear as the key in the key=value pairs in the results. If not defined, this will default to e.g. "Custom1" for the first set of annotation added.
  • File type : One of "bed", "gff", "gtf", "vcf", "bigwig". If not specified, VEP assumes the file is BED format.
  • Annotation type : One of "exact", "overlap". When using "exact" only annotations whose coordinates match exactly those of the variant will be reported. This would be suitable for position specific information such as conservation scores, allele frequencies or phenotype information. Using "overlap", any annotation that overlaps the variant by even 1bp will be reported. Only "overlap" is supported for GFF and GTF formats.
  • Force report coordinates : One of "0" or "1" (if left blank assumed to be "0") - if set to "1", this forces VEP to output the coordinates of an overlapping custom feature instead of any found identifier (or value in the case of bigWig) field. If set to "0" (the default), VEP will output the identifier field if one is found; if none is found, then the coordinates are used instead.
  • VCF fields : if any field names are specified that are found in the info field of the VCF, these will also be added as custom annotations. If using "exact" annotation type, allele-specific annotation will be retrieved. The INFO field name will be prefixed with the short name, e.g. using short name "test", the INFO field "foo" will appear as "test_FOO" in the VEP output. Alleles in the input and VCF entry are trimmed in both directions in an attempt to match complex or poorly formatted entries.

All options (apart from the filename) are optional and their absence will invoke the default behaviour.


Using remote files

The tabix utility makes it possible to read annotation files from remote locations, for example over HTTP or FTP protocols. In order to do this, the .tbi index file is downloaded locally (to the current working directory) when VEP is run. From this point on, only the portions of data requested by VEP (i.e. those overlapping the variants in your input file) are downloaded. Users should be aware, however, that it is still possible to cause problems with network traffic in this manner by requesting data for a large number of variants. Users with large amounts of data should download the annotation file locally rather than risk causing any issues!

bigWig files can also be used remotely in the same way as tabix-indexed files, although less stringent checks are carried out on VEP startup.