covviz 1.1.4

Multi-sample coverage browser

covviz

Coverage visualization; a many-sample coverage browser.

The aim of covviz is to highlight regions of significant (passing the user's z-score threshold) and sustained (beyond user specified distance) deviation from the majority of samples. Significance is determined using z-scores for all samples at all points using median absolute deviation. In order for regions to be highlighted, points must be significant consecutively throughout a user specified distance.

If you are analyzing a low number of samples, deviation may be irrelevant. In this case, we can set --min-samples to be greater than our sample total to skip Z-threshold calculation and plot coverages for all samples at all points.

The Python Package

covviz is installable via pip install -U covviz and analyzes a bed3+ output format.

Usage

To analyze your coverage data it needs to be in bed3+ format and include a header with sample IDs. The first three column headers are agnostic, but for samples test_sample1, test_sample2, and test_sample3, this would look like:

#chrom   start   end   sample1   sample2   sample3

Then CLI usage is:

covviz $bed

Custom Metadata (.ped)

There is support for non-indexcov .ped files, though you may have to change the default column IDs pertaining to the column which contains the sample ID and the sex of the sample.

covviz --ped $ped --sample-col sample_col --sex sex_col $bed

Annotation Tracks

Currently we support GFF, VCF, and BED. GFF tracks are added using --gff where features are 'gene' and attributes have 'Name='. Feature type and attribute regex can be configured using --gff-feature and --gff-attr.

VCF tracks (v4.1) are added with --vcf with the entire INFO string being displayed by default. Specifying --vcf-info with something like 'CLNDN=' will grab just that field when using ClinVar variants. Including large INFO strings for all variants can dramatically increase the size of the covviz report.

Region based annotation tracks can be added using --bed. The name field will be used to identify the regions when present.

Annotation tracks, --gff, --vcf, and --bed, may be specified multiple times.

In all cases, 'chr' will be stripped from the chromosome names.

The Nextflow Workflow

If you're starting with alignment indexes, this workflow aims to simply the process of obtaining coverage and generating the coverage browser.

We use indexcov to quickly estimate the coverage across samples then find regions of large, coverage-based anomalies.

The output of indexcov is then directly input into covviz.

Usage

Install nextflow:

curl -s https://get.nextflow.io | bash

Full nextflow installation instructions are available at: https://www.nextflow.io/

To simplify prerequisite software installations and software version tracking, we strongly recommend running covviz using Docker or Singularity. Docker installation instructions for your operating system are available at: https://docs.docker.com/install/

Then, with Docker or Singularity we run:

nextflow run brwnj/covviz -latest -profile docker \
    --indexes 'data/indexes/*.crai' \
    --fai data/g1k_v37_decoy.fa.fai \
    --gff data/Homo_sapiens.GRCh37.82.gff3.gz

Which gives us ./results/covviz_report.html.

Required arguments

• --indexes
  • quoted file path with wildcard ('*.crai') to cram or bam indexes
• --fai
  • file path to .fai reference index
• --gff
  • file path to gff matching genome build of --indexes

Workflow Options

• --outdir
  • output directory for results
  • default: "./results"
• --sexchroms
  • sex chromosomes as they are in --indexes
  • default: "X,Y"
• --exclude
  • regular expression of chromosomes to skip
  • default: "^GL|^hs|^chrEBV$|M$|MT$|^NC|random$|Un|^HLA\-|_alt$|hap\d+$"
• --zthreshold
  • a sample must greater than this many standard deviations in order to be found significant
  • default: 3.5
• --distancethreshold
  • consecutive significant points must span this distance in order to pass this filter
  • default: 150000
• --slop
  • leading and trailing segments added to significant regions to make them more visible
  • default: 500000
• --ped
  • custom metadata that will be merged with the .ped output of indexcov
  • default: false
• --samplecol
  • the column header for sample IDs in your custom ped file
  • default: "sample_id"

Report

Interactive example

See: https://brwnj.github.io/covviz/

Scaled chromosome coverage

Significant regions will be displayed in color atop a gray region which represents the upper and lower bounds of a given point minus any values deemed significant.

When plotting fewer samples than --min-samples, the gray area plot will not be displayed. Instead, all sample plot traces will be shown.

Proportions covered

The metadata table will be displayed below the plots.

Interaction

Clicking on plot traces highlights the line and searches the metadata. Double-clicking de-selects lines, resets the plot, and de-selects samples from the table. Clicking on the gene track launches a search for the gene's respective Gene Card. In cases where genes overlap, multiple windows/tabs will be opened.

License

covviz is free and unrestricted for non-commercial use. For commercial use, please contact [[e-mail]].