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Variant annotation in Python

Project description

`|Build Status| <>`_ `|Coverage
Status| <>`_
`|DOI| <>`_


Varcode is a library for working with genomic variant data in Python and
predicting the impact of those variants on protein sequences.


You can install varcode using
`pip <>`_:


pip install varcode

Optionally, you can pre-populate metadata caches through
`PyEnsembl <>`_ as follows:


# Downloads and installs the Ensembl releases (75 and 76)
pyensembl install --release 75 76

This will eliminate a potential delay of several minutes required to
install the relevant data when using the ``varcode`` for the first time.



import varcode

# Load TCGA MAF containing variants from their
variants = varcode.load_maf("tcga-ovarian-cancer-variants.maf")

### <VariantCollection from 'tcga-ovarian-cancer-variants.maf' with 6428 elements>
### -- Variant(contig=1, start=69538, ref=G, alt=A, genome=GRCh37)
### -- Variant(contig=1, start=881892, ref=T, alt=G, genome=GRCh37)
### -- Variant(contig=1, start=3389714, ref=G, alt=A, genome=GRCh37)
### -- Variant(contig=1, start=3624325, ref=G, alt=T, genome=GRCh37)
### ...

# you can index into a VariantCollection and get back a Variant object
variant = variants[0]

# groupby_gene_name returns a dictionary whose keys are gene names
# and whose values are themselves VariantCollections
gene_groups = variants.groupby_gene_name()

# get variants which affect the TP53 gene
TP53_variants = gene_groups["TP53"]

# predict protein coding effect of every TP53 variant on
# each transcript of the TP53 gene
TP53_effects = TP53_variants.effects()

### <EffectCollection with 789 elements>
### -- PrematureStop(variant=chr17 g.7574003G>A, transcript_name=TP53-001, transcript_id=ENST00000269305, effect_description=p.R342*)
### -- ThreePrimeUTR(variant=chr17 g.7574003G>A, transcript_name=TP53-005, transcript_id=ENST00000420246)
### -- PrematureStop(variant=chr17 g.7574003G>A, transcript_name=TP53-002, transcript_id=ENST00000445888, effect_description=p.R342*)
### -- FrameShift(variant=chr17 g.7574030_7574030delG, transcript_name=TP53-001, transcript_id=ENST00000269305, effect_description=p.R333fs)
### ...

premature_stop_effect = TP53_effects[0]


### 341

### Transcript(id=ENST00000269305, name=TP53-001, gene_name=TP53, biotype=protein_coding, location=17:7571720-7590856)

### 'TP53'

If you are looking for a quick start guide, you can check out `this
iPython book <./examples/varcode-quick_start.ipynb>`_ that demonstrates
simple use cases of Varcode

Effect Types

Effect type \| Description -----------: \| :-----------
*AlternateStartCodon* \| Replace annotated start codon with alternative
start codon (*e.g.* ``ATG>CAG``). *ComplexSubstitution* \| Insertion and
deletion of multiple amino acids. *Deletion* \| Coding mutation which
causes deletion of amino acid(s). *ExonLoss* \| Deletion of entire exon,
significantly disrupts protein. *ExonicSpliceSite* \| Mutation at the
beginning or end of an exon, may affect splicing. *FivePrimeUTR* \|
Variant affects 5' untranslated region before start codon.
*FrameShiftTruncation* \| A frameshift which leads immediately to a stop
codon (no novel amino acids created). *FrameShift* \| Out-of-frame
insertion or deletion of nucleotides, causes novel protein sequence and
often premature stop codon. *IncompleteTranscript* \| Can't determine
effect since transcript annotation is incomplete (often missing either
the start or stop codon). *Insertion* \| Coding mutation which causes
insertion of amino acid(s). *Intergenic* \| Occurs outside of any
annotated gene. *Intragenic* \|Within the annotated boundaries of a gene
but not in a region that's transcribed into pre-mRNA.
*IntronicSpliceSite* \| Mutation near the beginning or end of an intron
but less likely to affect splicing than donor/acceptor mutations.
*Intronic* \| Variant occurs between exons and is unlikely to affect
splicing. *NoncodingTranscript* \| Transcript doesn't code for a
protein. *PrematureStop* \| Insertion of stop codon, truncates protein.
*Silent* \| Mutation in coding sequence which does not change the amino
acid sequence of the translated protein. *SpliceAcceptor* \| Mutation in
the last two nucleotides of an intron, likely to affect splicing.
*SpliceDonor* \| Mutation in the first two nucleotides of an intron,
likely to affect splicing. *StartLoss* \| Mutation causes loss of start
codon, likely result is that an alternate start codon will be used
down-stream (possibly in a different frame). *StopLoss* \| Loss of stop
codon, causes extension of protein by translation of nucleotides from 3'
UTR. *Substitution* \| Coding mutation which causes simple substitution
of one amino acid for another. *ThreePrimeUTR* \| Variant affects 3'
untranslated region after stop codon of mRNA.

Coordinate System

Varcode currently uses a "base counted, one start" genomic coordinate
system, to match the Ensembl annotation database. We are planning to
switch over to "space counted, zero start" (interbase) coordinates,
since that system allows for more uniform logic (no special cases for
insertions). To learn more about genomic coordinate systems, read this
post <>`_.

.. |Build
Status| image::
.. |Coverage
Status| image::
.. |DOI| image::

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