somAgg code book general information

somAgg is split into 1371 'chunks' across the genome. To work with somAgg, you need to first identify the correct chunk for your region of interest. You can also use the FILTER, INFO and FORMAT fields for many queries.

somAgg chunks

To make it more manageable, somAgg comprises 1371 chunks. This is true for both the genotype VCFs and the functional annotation VCFs; where the chromosome, start, and stop chunk names are identical across data types.

To analyse the VCF for any particular region, gene or variant, you first need to identify the correct chunk.

Chunks are named in the following format:

somAgg_dr12_chromosome_start_stop.vcf.gz
e.g. somAgg_dr12_chr1_146620016_147701894.vcf.gz

List of chunk names and somAgg VCF files

The list of chunk names and full file paths to both the genotype and functional annotation VCFs can be found here. 

/gel_data_resources/main_programme/aggregation/aggregated_somatic_strelka/somAgg/v0.2/additional_data/chunk_names/somAgg_chunk_names.bed

Each of the 1,371 chunks is on a separate line and each line contains 7 fields:

Column number	Description	Example
1	Chromosome	chr1
2	Chunk start	1
3	Chunk stop	506426
4	Chromosome, start, stop (format 1)	chr1_1_506426
5	Chromosome, start, stop (format 2)	chr1:1-506426
6	Full path to genotype annotation VCF	/gel_data_resources/main_programme/aggregated_somatic_strelka/somAg/genomic_data/somAgg_dr12_chr1_1_506426.vcf.gz

Identifying which chunk to use

To find the right chunk file, you will need to:

1. Create a BED file of your regions of interest.
2. Intersect your BED file against the chunk BED file.

Create your own BED file

You firstly must create a regions file of your genes, variants or regions of interest. This must be a three or column tab-delimited file of chromosome, start, and stop (with an option fourth column of an identifier - i.e. a gene name). The file should have the .bed extension. There is no limit to how many lines you can have in this file.

Sort

Please pre-sort your data by chromosome and then by start position (sort -k1,1 -k2,2n in.bed in.sorted.bed)

Example:

chr2    213005363   213151603   IKZF2
chr7    50304716    50405101    IKZF1

Intersect the two files

Now you can intersect the bed file of chunk names with your regions file using bedtools as shown below: 

#!/bin/bash

module load bedtools/2.31.0

bedtools intersect -wo -a my_regions.bed -b somAgg_chunk_names.bed | cut -f 1-4,10

This will print out a six column tab-delimited file with the number of lines equalling the number of inputs in the regions file. It will have the following format:

Column number	Description	Example
1	Chromosome	chr2
2	Region start	213005363
3	Region stop	213151603
4	Region identifier	IKZF2
5	Full path to genotype annotation VCF	/gel_data_resources/main_programme/aggregation/aggregated_somatic_strelka/somAgg/v0.2/ /genomic_data/somAgg_dr12_chr2_211052166_213676386.vcf.gz

The full array of columns can also be printed by omitting the cut command. 

FILTER, INFO, and FORMAT fields in somAgg

You can also query somAgg using the FILTER, INFO and FORMAT tags within the VCFs (both the genotype VCFs and the functional annotation VCFs).

• The FILTER field has been forced to ".". 
• The INFO filed shows the per variant list of key-value pairs describing the variation (such as variant filter (flags, such as CommonGermlineVariant, or fraction of panel containing non-reference noise at the site(PNOISE)).
• The FORMAT field shows and extensible list of fields for describing the samples per variant (such as number of reads supporting each allele (AU:CU:GU:TU) or sample depth).

You can extract all tags per field using the code below which uses bcftools to view the header of a single chunk then extracts the specific field:

#!/bin/bash

module load bcftools/1.16

cd /gel_data_resources/main_programme/aggregation/aggregated_somatic_strelka/somAgg/v0.2

## This command will print out all of the FILTER tags in the VCF
bcftools view -h somAgg_dr12_chr1_104205047_106476576.vcf.gz | grep '#FILTER'

## This command will print out all of the INFO tags in the VCF
bcftools view -h somAgg_dr12_chr1_104205047_106476576.vcf.gz | grep '#INFO'

## This command will print out all of the FORMAT tags in the VCF
bcftools view -h somAgg_dr12_chr1_104205047_106476576.vcf.gz | grep '#FORMAT'