Best practices for multi-sample variant calling with DeepVariant (WES trio demonstration)

February 11, 2020 · View on GitHub

Overview

This document outlines all the steps and considerations for calling and merging a trio using DeepVariant and GLnexus. These best practices were developed and evaluated as described in the bioRxiv preprint Accurate, scalable cohort variant calls using DeepVariant and GLnexus.

The process involves 3 major stages: running DeepVariant to create individual genome call sets, running GLnexus to merge call sets, and analyzing the merged call set.

NOTE: This case study demonstrates an example of how to run DeepVariant end-to-end on one machine. The steps below were done on a machine with this example command to start a machine.

The steps in this document can be extended to merge larger cohorts as well.

See this workflow:

workflow

A few things to note before we start:

If you are looking for ways to run DeepVariant in larger batches, please refer to the third party solutions section.
It is recommended to use BAM files with original quality scores. In the case that BAM files went through recalibration, optional DV flags can be used in order to use original scores: --parse_sam_aux_fields, --use_original_quality_scores.
DeepVariant optionally allows gVCF output. This option is required for further GLnexus analysis in this document.

Dataset

The Whole Exome Sequencing (WES) dataset we're using is from:

ftp-trace.ncbi.nlm.nih.gov/giab/ftp/data/AshkenazimTrio/

HG002_NA24385_son
HG003_NA24149_father
HG004_NA24143_mother

Commands for downloading the input BAMs

Just for convenience, we use aria2 to download our data. You can change it to whatever other tools (wget, curl) that you prefer.

To install aria2, you can run: sudo apt-get -y install aria2

DIR="${PWD}/trio"
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/data/AshkenazimTrio/HG002_NA24385_son/OsloUniversityHospital_Exome/151002_7001448_0359_AC7F6GANXX_Sample_HG002-EEogPU_v02-KIT-Av5_AGATGTAC_L008.posiSrt.markDup.bam -o HG002.bam
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/data/AshkenazimTrio/HG002_NA24385_son/OsloUniversityHospital_Exome/151002_7001448_0359_AC7F6GANXX_Sample_HG002-EEogPU_v02-KIT-Av5_AGATGTAC_L008.posiSrt.markDup.bai -o HG002.bai
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/data/AshkenazimTrio/HG003_NA24149_father/OsloUniversityHospital_Exome/151002_7001448_0359_AC7F6GANXX_Sample_HG003-EEogPU_v02-KIT-Av5_TCTTCACA_L008.posiSrt.markDup.bam -o HG003.bam
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/data/AshkenazimTrio/HG003_NA24149_father/OsloUniversityHospital_Exome/151002_7001448_0359_AC7F6GANXX_Sample_HG003-EEogPU_v02-KIT-Av5_TCTTCACA_L008.posiSrt.markDup.bai -o HG003.bai
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/data/AshkenazimTrio/HG004_NA24143_mother/OsloUniversityHospital_Exome/151002_7001448_0359_AC7F6GANXX_Sample_HG004-EEogPU_v02-KIT-Av5_CCGAAGTA_L008.posiSrt.markDup.bam -o HG004.bam
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/data/AshkenazimTrio/HG004_NA24143_mother/OsloUniversityHospital_Exome/151002_7001448_0359_AC7F6GANXX_Sample_HG004-EEogPU_v02-KIT-Av5_CCGAAGTA_L008.posiSrt.markDup.bai -o HG004.bai

Command for downloading the reference file

aria2c -c -x10 -s10 -d "${DIR}" https://storage.googleapis.com/deepvariant/exome-case-study-testdata/hs37d5.fa.gz
gunzip ${DIR}/hs37d5.fa.gz
aria2c -c -x10 -s10 -d "${DIR}" https://storage.googleapis.com/deepvariant/exome-case-study-testdata/hs37d5.fa.fai

Command for downloading the input capture region BED file

aria2c -c -x10 -s10 -d "${DIR}" https://storage.googleapis.com/deepvariant/exome-case-study-testdata/agilent_sureselect_human_all_exon_v5_b37_targets.bed

Command for downloading the truth files

HG002:

aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/release/AshkenazimTrio/HG002_NA24385_son/NISTv3.3.2/GRCh37/HG002_GRCh37_GIAB_highconf_CG-IllFB-IllGATKHC-Ion-10X-SOLID_CHROM1-22_v.3.3.2_highconf_triophased.vcf.gz -o HG002_truth.vcf.gz
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/release/AshkenazimTrio/HG002_NA24385_son/NISTv3.3.2/GRCh37/HG002_GRCh37_GIAB_highconf_CG-IllFB-IllGATKHC-Ion-10X-SOLID_CHROM1-22_v.3.3.2_highconf_triophased.vcf.gz.tbi -o HG002_truth.vcf.gz.tbi
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/release/AshkenazimTrio/HG002_NA24385_son/NISTv3.3.2/GRCh37/HG002_GRCh37_GIAB_highconf_CG-IllFB-IllGATKHC-Ion-10X-SOLID_CHROM1-22_v.3.3.2_highconf_noinconsistent.bed -o HG002_truth.bed

HG003:

aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/release/AshkenazimTrio/HG003_NA24149_father/NISTv3.3.2/GRCh37/HG003_GRCh37_GIAB_highconf_CG-IllFB-IllGATKHC-Ion-10X_CHROM1-22_v.3.3.2_highconf.vcf.gz -o HG003_truth.vcf.gz
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/release/AshkenazimTrio/HG003_NA24149_father/NISTv3.3.2/GRCh37/HG003_GRCh37_GIAB_highconf_CG-IllFB-IllGATKHC-Ion-10X_CHROM1-22_v.3.3.2_highconf.vcf.gz.tbi -o HG003_truth.vcf.gz.tbi
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/release/AshkenazimTrio/HG003_NA24149_father/NISTv3.3.2/GRCh37/HG003_GRCh37_GIAB_highconf_CG-IllFB-IllGATKHC-Ion-10X_CHROM1-22_v.3.3.2_highconf_noinconsistent.bed -o HG003_truth.bed

HG004:

aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/release/AshkenazimTrio/HG004_NA24143_mother/NISTv3.3.2/GRCh37/HG004_GRCh37_GIAB_highconf_CG-IllFB-IllGATKHC-Ion-10X_CHROM1-22_v.3.3.2_highconf.vcf.gz -o HG004_truth.vcf.gz
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/release/AshkenazimTrio/HG004_NA24143_mother/NISTv3.3.2/GRCh37/HG004_GRCh37_GIAB_highconf_CG-IllFB-IllGATKHC-Ion-10X_CHROM1-22_v.3.3.2_highconf.vcf.gz.tbi -o HG004_truth.vcf.gz.tbi
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/release/AshkenazimTrio/HG004_NA24143_mother/NISTv3.3.2/GRCh37/HG004_GRCh37_GIAB_highconf_CG-IllFB-IllGATKHC-Ion-10X_CHROM1-22_v.3.3.2_highconf_noinconsistent.bed -o HG004_truth.bed

Install bcftools, samtools, htslib, if you don't already have them

Here are example commands used to install these tools. You should also look at http://www.htslib.org for official instructions.

sudo apt-get install -y build-essential libncurses5-dev zlib1g-dev libbz2-dev liblzma-dev tabix

wget https://github.com/samtools/samtools/releases/download/1.9/samtools-1.9.tar.bz2
tar -xvf samtools-1.9.tar.bz2
pushd samtools-1.9 && ./configure && make && sudo make install && popd

wget https://github.com/samtools/bcftools/releases/download/1.9/bcftools-1.9.tar.bz2
tar -xvf bcftools-1.9.tar.bz2
pushd bcftools-1.9 && ./configure && make && sudo make install && popd

wget https://github.com/samtools/htslib/releases/download/1.9/htslib-1.9.tar.bz2
tar -xvf htslib-1.9.tar.bz2
pushd htslib-1.9 && ./configure && make && sudo make install && popd

Run DeepVariant on trio to get 3 single sample VCFs

First, install docker if you don't have it yet: sudo apt-get -y install docker.io

With the example command below, it runs DeepVariant on the trio one by one. This is for demonstration only. If you're running this on a large cohort, running serially is not the most effective approach.

N_SHARDS=$(nproc)  # Or change to the number of cores you want to use
CAPTURE_BED=agilent_sureselect_human_all_exon_v5_b37_targets.bed
VERSION=0.9.0

declare -a trio=(HG002 HG003 HG004)
for SAMPLE in "${trio[@]}"
do
  BAM=${SAMPLE}.bam

  OUTPUT_VCF=${SAMPLE}.vcf.gz
  OUTPUT_GVCF=${SAMPLE}.g.vcf.gz

  time sudo docker run \
    -v "${DIR}":"/data" \
    google/deepvariant:${VERSION} \
    /opt/deepvariant/bin/run_deepvariant \
    --model_type=WES \
    --ref="/data/hs37d5.fa" \
    --reads="/data/${BAM}" \
    --regions="/data/${CAPTURE_BED}" \
    --output_vcf="/data/${OUTPUT_VCF}" \
    --output_gvcf="/data/${OUTPUT_GVCF}" \
    --num_shards=${N_SHARDS}
done

Merge the trio samples using GLnexus

Run GLnexus to merge 3 gVCFs

And then run GLnexus with this config:

sudo docker pull quay.io/mlin/glnexus:v1.2.2

time sudo docker run \
  -v "${DIR}":"/data" \
  quay.io/mlin/glnexus:v1.2.2 \
  /usr/local/bin/glnexus_cli \
  --config DeepVariantWES \
  --bed "/data/${CAPTURE_BED}" \
  /data/HG004.g.vcf.gz /data/HG003.g.vcf.gz /data/HG002.g.vcf.gz \
  | bcftools view - | bgzip -c > ${DIR}/deepvariant.cohort.vcf.gz

When we ran on this WES trio, it took only about 13 seconds. For more details on performance, see GLnexus performance guide. And, if you are merging a WGS cohort, please use the --config DeepVariantWGS. The corresponding params can be found in WGS params and WES params.

Annotate the merged VCF with Mendelian discordance information using RTG Tools

Create an SDF template from our reference file:

sudo docker run \
  -v "${DIR}":"/data" \
  realtimegenomics/rtg-tools format \
  -o /data/hs37d5.sdf /data/hs37d5.fa

Create a PED file $DIR/trio.ped that looks like this (with the sample name of the trio):

#PED format pedigree
#
#fam-id/ind-id/pat-id/mat-id: 0=unknown
#sex: 1=male; 2=female; 0=unknown
#phenotype: -9=missing, 0=missing; 1=unaffected; 2=affected
#
#fam-id ind-id pat-id mat-id sex phen
1 Sample_Diag-excap51-HG002-EEogPU Sample_Diag-excap51-HG003-EEogPU Sample_Diag-excap51-HG004-EEogPU 1 0
1 Sample_Diag-excap51-HG003-EEogPU 0 0 1 0
1 Sample_Diag-excap51-HG004-EEogPU 0 0 2 0

Annotate merged VCF with RTG Tools

sudo docker run \
  -v "${DIR}":"/data" \
  realtimegenomics/rtg-tools mendelian \
  -i /data/deepvariant.cohort.vcf.gz \
  -o /data/deepvariant.annotated.vcf.gz \
  --pedigree=/data/trio.ped \
  -t /data/hs37d5.sdf \
  | tee ${DIR}/deepvariant.input_rtg_output.txt

The output is:

Checking: /data/deepvariant.cohort.vcf.gz
Family: [Sample_Diag-excap51-HG003-EEogPU + Sample_Diag-excap51-HG004-EEogPU] -> [Sample_Diag-excap51-HG002-EEogPU]
1 non-pass records were skipped
Concordance Sample_Diag-excap51-HG002-EEogPU: F:59682/60267 (99.03%)  M:60059/60245 (99.69%)  F+M:59329/60107 (98.71%)
Sample Sample_Diag-excap51-HG002-EEogPU has less than 99.0 concordance with both parents. Check for incorrect pedigree or sample mislabelling.
862/60626 (1.42%) records did not conform to expected call ploidy
60430/60626 (99.68%) records were variant in at least 1 family member and checked for Mendelian constraints
266/60430 (0.44%) records had indeterminate consistency status due to incomplete calls
803/60430 (1.33%) records contained a violation of Mendelian constraints

From this report, we know that there is a 1.33% Mendelian violation rate, and 0.44% of the records had incomplete calls (with .) so RTG couldn't determine whether there is violation or not.

Single sample quality metrics

In addition to the cohort quality statistics, for completeness we generate single-sample quality metrics.

ti/tv ratio

We run bcftools stats on the 3 VCF outputs. Since our DeepVariant run already constrained to just the capture regions, no need to specify it again here. We had to pass in the -f PASS flag so that only the PASS calls are considered.

declare -a trio=(HG002 HG003 HG004)
for SAMPLE in "${trio[@]}"
do
  bcftools stats -f PASS \
    ${DIR}/${SAMPLE}.vcf.gz \
  > ${DIR}/${SAMPLE}.stats
done

Sample	[3]ts	[4]tv	[5]ts/tv	[6]ts (1st ALT)	[7]tv (1st ALT)	[8]ts/tv (1st ALT)
HG002	30171	11811	2.55	30158	11788	2.56
HG003	30088	11900	2.53	30075	11874	2.53
HG004	30310	11993	2.53	30296	11971	2.53

If you want to restrict to the truth BED files, use this command:

declare -a trio=(HG002 HG003 HG004)
for SAMPLE in "${trio[@]}"
do
  bcftools stats -f PASS \
    -T ${DIR}/${SAMPLE}_truth.bed \
    ${DIR}/${SAMPLE}.vcf.gz \
  > ${DIR}/${SAMPLE}.with_truth_bed.stats
done

Which resulted in this table:

Sample	[3]ts	[4]tv	[5]ts/tv	[6]ts (1st ALT)	[7]tv (1st ALT)	[8]ts/tv (1st ALT)
HG002	24472	9253	2.64	24467	9243	2.65
HG003	24169	9185	2.63	24166	9177	2.63
HG004	24315	9334	2.60	24308	9327	2.61

Rtg vcfstats

declare -a trio=(HG002 HG003 HG004)
for SAMPLE in "${trio[@]}"
do
  sudo docker run \
  -v "${DIR}":"/data" \
  realtimegenomics/rtg-tools vcfstats \
  /data/${SAMPLE}.vcf.gz \
  > ${DIR}/${SAMPLE}.vcfstats
done

which shows the following:

HG002:

Location                     : /data/HG002.vcf.gz
Failed Filters               : 11500
Passed Filters               : 45670
SNPs                         : 41946
MNPs                         : 0
Insertions                   : 1921
Deletions                    : 1784
Indels                       : 17
Same as reference            : 2
SNP Transitions/Transversions: 2.55 (42027/16451)
Total Het/Hom ratio          : 1.53 (27585/18083)
SNP Het/Hom ratio            : 1.54 (25438/16508)
MNP Het/Hom ratio            : - (0/0)
Insertion Het/Hom ratio      : 1.16 (1033/888)
Deletion Het/Hom ratio       : 1.60 (1097/687)
Indel Het/Hom ratio          : - (17/0)
Insertion/Deletion ratio     : 1.08 (1921/1784)
Indel/SNP+MNP ratio          : 0.09 (3722/41946)

HG003:

Location                     : /data/HG003.vcf.gz
Failed Filters               : 12048
Passed Filters               : 45622
SNPs                         : 41945
MNPs                         : 0
Insertions                   : 1906
Deletions                    : 1751
Indels                       : 18
Same as reference            : 2
SNP Transitions/Transversions: 2.51 (41888/16665)
Total Het/Hom ratio          : 1.52 (27501/18119)
SNP Het/Hom ratio            : 1.53 (25364/16581)
MNP Het/Hom ratio            : - (0/0)
Insertion Het/Hom ratio      : 1.20 (1041/865)
Deletion Het/Hom ratio       : 1.60 (1078/673)
Indel Het/Hom ratio          : - (18/0)
Insertion/Deletion ratio     : 1.09 (1906/1751)
Indel/SNP+MNP ratio          : 0.09 (3675/41945)

HG004:

Location                     : /data/HG004.vcf.gz
Failed Filters               : 11918
Passed Filters               : 45967
SNPs                         : 42261
MNPs                         : 0
Insertions                   : 1910
Deletions                    : 1772
Indels                       : 21
Same as reference            : 3
SNP Transitions/Transversions: 2.54 (41895/16482)
Total Het/Hom ratio          : 1.61 (28344/17620)
SNP Het/Hom ratio            : 1.63 (26169/16092)
MNP Het/Hom ratio            : - (0/0)
Insertion Het/Hom ratio      : 1.20 (1041/869)
Deletion Het/Hom ratio       : 1.69 (1113/659)
Indel Het/Hom ratio          : - (21/0)
Insertion/Deletion ratio     : 1.08 (1910/1772)
Indel/SNP+MNP ratio          : 0.09 (3703/42261)

Run hap.py to calculate the accuracy of DeepVariant generated call sets

sudo docker pull pkrusche/hap.py

declare -a trio=(HG002 HG003 HG004)
for SAMPLE in "${trio[@]}"
do
  sudo docker run -i \
    -v "${DIR}":"/data" \
    pkrusche/hap.py /opt/hap.py/bin/hap.py \
    "/data/${SAMPLE}_truth.vcf.gz" \
    "/data/${SAMPLE}.vcf.gz" \
    -f "/data/${SAMPLE}_truth.bed" \
    -T "/data/${CAPTURE_BED}" \
    -r "/data/hs37d5.fa" \
    -o "/data/${SAMPLE}.happy.output" \
    --engine=vcfeval > ${DIR}/${SAMPLE}.stdout
done

Accuracy F1 scores:

Sample	Indel	SNP
HG002	0.973295	0.999318
HG003	0.969842	0.998980
HG004	0.974818	0.999183