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Variant Effect Predictor Data formats


Input

Both the web and script version of VEP can use the same input formats. Formats can be auto-detected by the VEP script, but must be manually selected when using the web interface.

VEP can use different input formats:

Note

VEP can read compressed (gzipped) input file of any format listed above, e.g.:

 ./vep -i input.vcf.gz -o output.txt


Default VEP input

The default format is a simple whitespace-separated format (columns may be separated by space or tab characters), containing five required columns plus an optional identifier column:

  1. chromosome - just the name or number, with no 'chr' prefix
  2. start
  3. end
  4. allele - pair of alleles separated by a '/', with the reference allele first
  5. strand - defined as + (forward) or - (reverse).
  6. identifier - this identifier will be used in VEP's output. If not provided, VEP will construct an identifier from the given coordinates and alleles.
1   881907    881906    -/C   +
5   140532    140532    T/C   +
12  1017956   1017956   T/A   +
2   946507    946507    G/C   +
14  19584687  19584687  C/T   -
19  66520     66520     G/A   +    var1
8   150029    150029    A/T   +    var2

An insertion (of any size) is indicated by start coordinate = end coordinate + 1. For example, an insertion of 'C' between nucleotides 12600 and 12601 on the forward strand of chromosome 8 is indicated as follows:

8   12601     12600     -/C   +

A deletion is indicated by the exact nucleotide coordinates. For example, a three base pair deletion of nucleotides 12600, 12601, and 12602 of the reverse strand of chromosome 8 will be:

8   12600     12602     CGT/- -


VCF

VEP also supports using VCF (Variant Call Format) version 4.0. This is a common format used by the 1000 genomes project, and can be produced as an output format by many variant calling tools.

Users using VCF should note a peculiarity in the difference between how Ensembl and VCF describe unbalanced variants. For any unbalanced variant (i.e. insertion, deletion or unbalanced substitution), the VCF specification requires that the base immediately before the variant should be included in both the reference and variant alleles. This also affects the reported position i.e. the reported position will be one base before the actual site of the variant.

In order to parse this correctly, VEP needs to convert such variants into Ensembl-type coordinates, and it does this by removing the additional base and adjusting the coordinates accordingly. This means that if an identifier is not supplied for a variant (in the 3rd column of the VCF), then the identifier constructed and the position reported in VEP's output file will differ from the input.

This problem can be overcome with the following:

  1. ensuring each variant has a unique identifier specified in the 3rd column of the VCF
  2. using VCF format as output (--vcf) - this preserves the formatting of your input coordinates and alleles
  3. using --minimal and --allele_number (see Complex VCF entries).

The following examples illustrate how VCF describes a variant and how it is handled internally by VEP. Consider the following aligned sequences (for the purposes of discussion on chromosome 20):

Ref: a t C g a // C is the reference base
1 : a t G g a // C base is a G in individual 1
2 : a t - g a // C base is deleted w.r.t. the reference in individual 2
3 : a t CAg a // A base is inserted w.r.t. the reference sequence in individual 3

Individual 1

The first individual shows a simple balanced substitution of G for C at base 3. This is described in a compatible manner in VCF and Ensembl styles. Firstly, in VCF:

20   3   .   C   G   .   PASS   .

And in Ensembl format:

 20   3   3   C/G   +

Individual 2

The second individual has the 3rd base deleted relative to the reference. In VCF, both the reference and variant allele columns must include the preceding base (T) and the reported position is that of the preceding base:

20   2   .   TC   T   .   PASS   .

In Ensembl format, the preceding base is not included, and the start/end coordinates represent the region of the sequence deleted. A "-" character is used to indicate that the base is deleted in the variant sequence:

20   3   3   C/-   +

The upshot of this is that while in the VCF input file the position of the variant is reported as 2, in the output file from VEP the position will be reported as 3. If no identifier is provided in the third column of the VCF, then the constructed identifier will be:

20_3_C/-

Individual 3

The third individual has an "A" inserted between the 3rd and 4th bases of the sequence relative to the reference. In VCF, as for the deletion, the base before the insertion is included in both the reference and variant allele columns, and the reported position is that of the preceding base:

20   3   .   C   CA   .   PASS   .

In Ensembl format, again the preceding base is not included, and the start/end positions are "swapped" to indicate that this is an insertion. Similarly to a deletion, a "-" is used to indicate no sequence in the reference:

 20   4   3   -/A   +

Again, the output will appear different, and the constructed identifier may not be what is expected:

20_3_-/A

Using VCF format output, or adding unique identifiers to the input (in the third VCF column), can mitigate this issue.


Complex VCF entries

For VCF entries with multiple alternate alleles, VEP will only trim the leading base from alleles if all REF and ALT alleles start with the same base:

20   3   .   C   CAAG,CAAGAAG   .   PASS   .

This will be considered internally by VEP as equivalent to:

20   4   3   -/AAG/AAGAAG   +

Now consider the case where a single VCF line contains a representation of both a SNV and an insertion:

20   3   .   C   CAAAG,G   .   PASS   .

Here the input alleles will remain unchanged, and VEP will consider the first REF/ALT pair as a substitution of C for CAAG, and the second as a C/G SNV:

20   3   3   C/CAAG/G   +

To modify this behaviour, VEP script users may use --minimal. This flag forces VEP to consider each REF/ALT pair independently, trimming identical leading and trailing bases from each as appropriate. Since this can lead to confusing output regarding coordinates etc, it is not the default behaviour. It is recommended to use the --allele_number flag to track the correspondence between alleles as input and how they appear in the output.



VCF - Structural variants

VEP can also call consequences on structural variants encoded in tab-delimited or VCF format. To recognise a variant as a structural variant, the allele string (or "SVTYPE" INFO field in VCF) must be set to one of the currently recognised values:

  • INS - insertion
  • DEL - deletion
  • DUP - duplication
  • TDUP - tandem duplication

Examples of structural variants encoded in tab-delimited format:

1    160283    471362    DUP
1    1385015   1387562   DEL

Examples of structural variants encoded in VCF format:

#CHROM  POS     ID   REF  ALT    QUAL  FILTER  INFO                    FORMAT
1       160283  sv1  .    <DUP>  .     .       SVTYPE=DUP;END=471362   .
1       1385015 sv2  .    <DEL>  .     .       SVTYPE=DEL;END=1387562  .

See the VCF definition document for more detail on how to describe structural variants in VCF format.



HGVS identifiers

See https://varnomen.hgvs.org for details. These must be relative to genomic or Ensembl transcript coordinates.

It also is possible to use RefSeq transcripts in both the web interface and the VEP script (see script documentation): this works for RefSeq transcripts that align to the genome correctly.

Examples:

ENST00000207771.3:c.344+626A>T
ENST00000471631.1:c.28_33delTCGCGG
ENST00000285667.3:c.1047_1048insC
5:g.140532T>C

Examples using RefSeq identifiers (using --refseq in the VEP script, or select the otherfeatures transcript database on the web interface and input type of HGVS):

NM_153681.2:c.7C>T
NM_005239.4:c.190G>A
NM_001025204.1:c.336G>A

HGVS protein notations may also be used, provided that they unambiguously map to a single genomic change. Due to redundancy in the amino acid code, it is not always possible to work out the corresponding genomic sequence change for a given protein sequence change. The following example is for a permissable protein notation in dog (Canis familiaris):

ENSCAFP00000040171.1:p.Thr92Asn

HGVS notations may also be given in LRG coordinates:

LRG_1t1:c.841G>T
LRG_1:g.10006G>T


Variant identifiers

These should be e.g. dbSNP rsIDs, or any synonym for a variant present in the Ensembl Variation database. See here for a list of identifier sources in Ensembl.



Genomic SPDI notation

VEP can also support genomic SPDI notation which uses four fields delimited by colons S:P:D:I (Sequence:Position:Deletion:Insertion). See here for details.

Examples:

NC_000016.10:68684738:G:A
NC_000017.11:43092199:GCTTTT:
NC_000013.11:32315789::C
NC_000016.10:68644746:AA:GTA
16:68684738:2:AC


REST-style regions

VEP's region REST endoint requires variants are described as [chr]:[start]-[end]:[strand]/[allele]. This follows the same conventions as the default input format described above, with the key difference being that this format does not require the reference (REF) allele to be included; VEP will look up the reference allele using either a provided FASTA file (preferred) or Ensembl core database. Strand is optional and defaults to 1 (forward strand).

# SNP
5:140532-140532:1/C

# SNP (reverse strand)
14:19584687-19584687:-1/T

# insertion
1:881907-881906:1/C

# 5bp deletion
2:946507-946511:1/-



Output

VEP can return the results in different formats:

Along with the results VEP computes and returns some statistics.



Default VEP output

The default output format ("VEP" format when downloading from the web interface) is a 14 column tab-delimited file. Empty values are denoted by '-'. The output columns are:

  1. Uploaded variation - as chromosome_start_alleles
  2. Location - in standard coordinate format (chr:start or chr:start-end)
  3. Allele - the variant allele used to calculate the consequence
  4. Gene - Ensembl stable ID of affected gene
  5. Feature - Ensembl stable ID of feature
  6. Feature type - type of feature. Currently one of Transcript, RegulatoryFeature, MotifFeature.
  7. Consequence - consequence type of this variant
  8. Position in cDNA - relative position of base pair in cDNA sequence
  9. Position in CDS - relative position of base pair in coding sequence
  10. Position in protein - relative position of amino acid in protein
  11. Amino acid change - only given if the variant affects the protein-coding sequence
  12. Codon change - the alternative codons with the variant base in upper case
  13. Co-located variation - known identifier of existing variant
  14. Extra - this column contains extra information as key=value pairs separated by ";", see below.

Other output fields: Show fields

Example of VEP default output format:

11_224088_C/A    11:224088   A  ENSG00000142082  ENST00000525319  Transcript         missense_variant           742  716  239  T/N  aCc/aAc  -  SIFT=deleterious(0);PolyPhen=unknown(0)
11_224088_C/A    11:224088   A  ENSG00000142082  ENST00000534381  Transcript         5_prime_UTR_variant        -    -    -    -    -        -  -
11_224088_C/A    11:224088   A  ENSG00000142082  ENST00000529055  Transcript         downstream_variant         -    -    -    -    -        -  -
11_224585_G/A    11:224585   A  ENSG00000142082  ENST00000529937  Transcript         intron_variant             -    -    -    -    -        -  HGVSc=ENST00000529937.1:c.136-346G>A
22_16084370_G/A  22:16084370 A  -                ENSR00000615113  RegulatoryFeature  regulatory_region_variant  -    -    -    -    -        -  -

The VEP script will also add a header to the output file. This contains information about the databases connected to, and also a key describing the key/value pairs used in the extra column.

## ENSEMBL VARIANT EFFECT PREDICTOR v98.0
## Output produced at 2017-03-21 14:51:27
## Connected to homo_sapiens_core_98_38 on ensembldb.ensembl.org
## Using cache in /homes/user/.vep/homo_sapiens/98_GRCh38
## Using API version 98, DB version 98
## polyphen version 2.2.2
## sift version sift5.2.2
## COSMIC version 78
## ESP version 20141103
## gencode version GENCODE 25
## genebuild version 2014-07
## HGMD-PUBLIC version 20162
## regbuild version 16
## assembly version GRCh38.p7
## ClinVar version 201610
## dbSNP version 147
## Column descriptions:
## Uploaded_variation : Identifier of uploaded variant
## Location : Location of variant in standard coordinate format (chr:start or chr:start-end)
## Allele : The variant allele used to calculate the consequence
## Gene : Stable ID of affected gene
## Feature : Stable ID of feature
## Feature_type : Type of feature - Transcript, RegulatoryFeature or MotifFeature
## Consequence : Consequence type
## cDNA_position : Relative position of base pair in cDNA sequence
## CDS_position : Relative position of base pair in coding sequence
## Protein_position : Relative position of amino acid in protein
## Amino_acids : Reference and variant amino acids
## Codons : Reference and variant codon sequence
## Existing_variation : Identifier(s) of co-located known variants
## Extra column keys:
## IMPACT : Subjective impact classification of consequence type
## DISTANCE : Shortest distance from variant to transcript
## STRAND : Strand of the feature (1/-1)
## FLAGS : Transcript quality flags


Tab-delimited output

The --tab flag instructs VEP to write output as a tab-delimited table.
This differs from the default output format in that each individual field from the "Extra" field is written to a separate tab-delimited column.
This makes the output more suitable for import into spreadsheet programs such as Excel.
Furthermore the header is the same as the one for the VEP default output format and this is also the format used when selecting the "TXT" option on the VEP web interface.

Example of VEP tab-delimited output format:

#Uploaded_variation  Location   Allele  Gene             Feature          Feature_type  Consequence                            cDNA_position  CDS_position  Protein_position  Amino_acids  Codons   Existing_variation  IMPACT    DISTANCE  STRAND  FLAGS 
11_224088_C/A        11:224088  A       ENSG00000142082  ENST00000525319  Transcript    missense_variant                       742            716           239               S/I          aGc/aTc  -                   MODERATE  -         -1      - 
11_224088_C/A        11:224088  A       ENSG00000142082  ENST00000534381  Transcript    downstream_gene_variant                -              -             -                 -            -        -                   MODIFIER  1674      -1      -
11_224088_C/A        11:224088  A       ENSG00000142082  ENST00000529055  Transcript    downstream_gene_variant                -              -             -                 -            -        -                   MODIFIER  134       -1      -
11_224585_G/A        11:224585  A       ENSG00000142082  ENST00000529937  Transcript    intron_variant,NMD_transcript_variant  -              -             -                 -            -        -                   MODIFIER  -         -1      -

The choice and order of columns in the output may be configured using --fields. For instance:

./vep -i examples/homo_sapiens_GRCh38.vcf --cache --force_overwrite --tab --fields "Uploaded variation,Location,Allele,Gene"



VCF output

The VEP script can also generate VCF output using the --vcf flag.

Main information about the specificity of the VEP VCF output format:

  • Consequences are added in the INFO field of the VCF file, using the key "CSQ" (you can change it using --vcf_info_field).
  • Data fields are encoded separated by the character "|" (pipe). The order of fields is written in the VCF header. Unpopulated fields are represented by an empty string.
  • Output fields in the "CSQ" INFO field can be configured by using --fields.
  • Each prediction, for a given variant, is separated by the character "," in the CSQ INFO field (e.g. when a variant overlaps more than 1 transcript)

Here is a list of the (default) fields you can find within the CSQ field:

Allele|Consequence|IMPACT|SYMBOL|Gene|Feature_type|Feature|BIOTYPE|EXON|INTRON|HGVSc|HGVSp|cDNA_position|CDS_position|Protein_position|Amino_acids|Codons|Existing_variation|DISTANCE|STRAND|FLAGS|SYMBOL_SOURCE|HGNC_ID

Example of VEP command using the --vcf and --fields options:

./vep -i examples/homo_sapiens_GRCh38.vcf --cache --force_overwrite --vcf --fields "Allele,Consequence,Feature_type,Feature"

VCFs produced by VEP can be filtered by filter_vep.pl in the same way as standard format output files.

If the input format was VCF, the file will remain unchanged save for the addition of the CSQ field and the header (unless using any filtering). If an existing CSQ field is found, it will be replaced by the one added by the VEP (use --keep_csq to preserve it).

Custom data added with --custom are added as separate fields, using the key specified for each data file.

Commas in fields are replaced with ampersands (&) to preserve VCF format.

##INFO=<ID=CSQ,Number=.,Type=String,Description="Consequence annotations from Ensembl VEP. Format: Allele|Consequence|IMPACT|SYMBOL|Gene|Feature_type|Feature|BIOTYPE|EXON|INTRON|HGVSc|HGVSp|cDNA_position|CDS_position|Protein_position">
#CHROM  POS       ID          REF  ALT  QUAL  FILTER  INFO
21      26978790  rs75377686  T    C    .     .       CSQ=C|missense_variant|MODERATE|MRPL39|ENSG00000154719|Transcript|ENST00000419219|protein_coding|2/8||ENST00000419219.1:c.251A>G|ENSP00000404426.1:p.Asn84Ser|260|251|84


JSON output

VEP can produce output in the form of serialised JSON objects using the --json flag. JSON is a serialisation format that can be parsed and processed easily by many packages and programming languages; it is used as the default output format for Ensembl's REST server.

Each input variant is reported as a single JSON object which constitutes one line of the output file. The JSON object is structured somewhat differently to the other VEP output formats, in that per-variant fields (e.g. co-located existing variant details) are reported only once. Consequences are grouped under the feature type that they affect (Transcript, Regulatory Feature, etc). The original input line (e.g. from VCF input) is reported under the "input" key in order to aid aligning input with output.

Here follows an example of JSON output (prettified and redacted for display here):

{
  "input": "1 230845794 test1 A G . . .",
  "id": "test1",
  "seq_region_name": "1",
  "start": 230845794,
  "end": 230845794,
  "strand": 1,
  "allele_string": "A/G",
  "most_severe_consequence": "missense_variant",
  "colocated_variants": [
    {
      "id": "rs699",
      "seq_region_name": "1",
      "start": 230845794,
      "end": 230845794,
      "strand": 1,
      "allele_string": "A/G",
      "minor_allele": "A",
      "minor_allele_freq": 0.3384,
      "afr_allele": "A",
      "afr_maf": 0.13,
      "amr_allele": "A",
      "amr_maf": 0.36,
      "asn_allele": "A",
      "asn_maf": 0.16,
      "eur_allele": "A",
      "eur_maf": 0.41,
      "pubmed": [
        18513389,
        23716723
      ]
    },
    {
      "seq_region_name": "1",
      "strand": 1,
      "id": "COSM425562",
      "allele_string": "A/G",
      "start": 230845794,
      "end": 230845794
    }
  ],
  "transcript_consequences": [
    {
      "variant_allele": "G",
      "consequence_terms": [
        "missense_variant"
      ],
      "gene_id": "ENSG00000135744",
      "gene_symbol": "AGT",
      "gene_symbol_source": "HGNC",
      "transcript_id": "ENST00000366667",
      "biotype": "protein_coding",
      "strand": -1,
      "cdna_start": 1018,
      "cdna_end": 1018,
      "cds_start": 803,
      "cds_end": 803,
      "protein_start": 268,
      "protein_end": 268,
      "codons": "aTg/aCg",
      "amino_acids": "M/T",
      "polyphen_prediction": "benign",
      "polyphen_score": 0,
      "sift_prediction": "tolerated",
      "sift_score": 1,
      "hgvsc": "ENST00000366667.4:c.803T>C",
      "hgvsp": "ENSP00000355627.4:p.Met268Thr"
    }
  ],
  "regulatory_feature_consequences": [
    {
      "variant_allele": "G",
      "consequence_terms": [
        "regulatory_region_variant"
      ],
      "regulatory_feature_id": "ENSR00001529861"
    }
  ]
}

In accordance with JSON conventions, all keys are lower-case. Some keys also have different names and structures to those found in the other VEP output formats:

Key JSON equivalent(s) Notes
Consequence consequence_terms
Gene gene_id
Feature transcript_id, regulatory_feature_id, motif_feature_id Consequences are grouped under the feature type they affect
ALLELE variant_allele
SYMBOL gene_symbol
SYMBOL_SOURCE gene_symbol_source
ENSP protein_id
OverlapBP bp_overlap
OverlapPC percentage_overlap
Uploaded_variation id
Location seq_region_name, start, end, strand The variant's location field is broken down into constituent coordinate parts for clarity. "seq_region_name" is used in place of "chr" or "chromosome" for consistency with other parts of Ensembl's REST API
GMAF minor_allele, minor_allele_freq
*_maf *_allele, *_maf
cDNA_position cdna_start, cdna_end
CDS_position cds_start, cds_end
Protein_position protein_start, protein_end
SIFT sift_prediction, sift_score
PolyPhen polyphen_prediction, polyphen_score


Statistics

VEP writes an HTML file containing statistics pertaining to the results of your job; it is named [output_file]_summary.html (with the default options the file will be named variant_effect_output.txt_summary.html). To view it you should open the file in your web browser.

To prevent VEP writing a stats file, use the flag --no_stats. To have VEP write a machine-readable text file in place of the HTML, use --stats_text. To change the name of the stats file from the default, use --stats_file [file].

The page contains several sections:

General statistics

This section contains two tables. The first describes the cache and/or database used, the version of VEP, species, command line parameters, input/output files and run time. The second table contains information about the number of variants, and the number of genes, transcripts and regulatory features overlapped by the input.

Charts and tables

There then follows several charts, most with accompanying tables. Tables and charts are interactive; clicking on a row to highlight it in the table will highlight the relevant segment in the chart, and vice versa.