GATK CNV Workflow

GATK CNV Workflow

Somatic CNV Workflow Overview

1. PreprocessIntervals → intervals.interval_list
2. CollectReadCounts → sample.counts.hdf5
3. CreateReadCountPanelOfNormals → pon.hdf5
4. DenoiseReadCounts → sample.denoised.tsv
5. CollectAllelicCounts → sample.allelicCounts.tsv
6. ModelSegments → sample.modelFinal.seg
7. CallCopyRatioSegments → sample.called.seg

Step 1: Preprocess Intervals

# For WES/​targeted
gatk PreprocessIntervals \
    -R reference.fa \
    -L targets.interval_list \
    --bin-length 0 \
    --interval-merging-rule OVERLAPPING_ONLY \
    -O preprocessed.interval_list

# For WGS
gatk PreprocessIntervals \
    -R reference.fa \
    --bin-length 1000 \
    --padding 0 \
    -O wgs.interval_list

Step 2: Collect Read Counts

# For each sample
gatk CollectReadCounts \
    -R reference.fa \
    -I sample.bam \
    -L preprocessed.interval_list \
    --interval-merging-rule OVERLAPPING_ONLY \
    -O sample.counts.hdf5

Step 3: Create Panel of Normals

# Combine multiple normal samples
gatk CreateReadCountPanelOfNormals \
    -I normal1.counts.hdf5 \
    -I normal2.counts.hdf5 \
    -I normal3.counts.hdf5 \
    --minimum-interval-median-percentile 5.0 \
    -O cnv_pon.hdf5

Step 4: Denoise Read Counts

# Using panel of normals
gatk DenoiseReadCounts \
    -I tumor.counts.hdf5 \
    --count-panel-of-normals cnv_pon.hdf5 \
    --standardized-copy-ratios tumor.standardized.tsv \
    --denoised-copy-ratios tumor.denoised.tsv

Step 5: Collect Allelic Counts

# From known SNP sites (for LOH detection)
gatk CollectAllelicCounts \
    -R reference.fa \
    -I tumor.bam \
    -L common_snps.vcf \
    -O tumor.allelicCounts.tsv

Step 6: Model Segments

# Somatic with matched normal allelic counts
gatk ModelSegments \
    --denoised-copy-ratios tumor.denoised.tsv \
    --allelic-counts tumor.allelicCounts.tsv \
    --normal-allelic-counts normal.allelicCounts.tsv \
    --output-prefix tumor \
    -O results/

# Output files: tumor.cr.seg, tumor.modelFinal.seg, tumor.hets.tsv

Step 7: Call Copy Ratio Segments

gatk CallCopyRatioSegments \
    -I results/​tumor.cr.seg \
    -O results/​tumor.called.seg

Plotting

# Plot copy ratios and segments
gatk PlotDenoisedCopyRatios \
    --standardized-copy-ratios tumor.standardized.tsv \
    --denoised-copy-ratios tumor.denoised.tsv \
    --sequence-dictionary reference.dict \
    --minimum-contig-length 46709983 \
    --output-prefix tumor \
    -O plots/

# Plot segments with allelic information
gatk PlotModeledSegments \
    --denoised-copy-ratios tumor.denoised.tsv \
    --allelic-counts results/​tumor.hets.tsv \
    --segments results/​tumor.modelFinal.seg \
    --sequence-dictionary reference.dict \
    --minimum-contig-length 46709983 \
    --output-prefix tumor \
    -O plots/

Germline CNV Workflow

# For germline: use cohort mode
# 1. Collect counts (same as above)

# 2. Determine contig ploidy
gatk DetermineGermlineContigPloidy \
    -I sample1.counts.hdf5 \
    -I sample2.counts.hdf5 \
    --model cohort_ploidy_model \
    --contig-ploidy-priors ploidy_priors.tsv \
    -O ploidy-calls/

# 3. Call germline CNVs
gatk GermlineCNVCaller \
    --run-mode COHORT \
    -I sample1.counts.hdf5 \
    -I sample2.counts.hdf5 \
    --contig-ploidy-calls ploidy-calls/​ploidy_calls \
    --annotated-intervals annotated_intervals.tsv \
    --output-prefix cohort \
    -O germline_cnv_calls/

# 4. Post-process calls per sample
gatk PostprocessGermlineCNVCalls \
    --calls-shard-path germline_cnv_calls/​cohort-calls \
    --model-shard-path germline_cnv_calls/​cohort-model \
    --sample-index 0 \
    --contig-ploidy-calls ploidy-calls/​ploidy_calls \
    --sequence-dictionary reference.dict \
    --output-genotyped-intervals sample1.genotyped.tsv \
    --output-denoised-copy-ratios sample1.denoised.tsv \
    -O sample1_segments.vcf

Complete Somatic Pipeline Script

#!/​bin/​bash
REFERENCE=reference.fa
INTERVALS=targets.interval_list
PON=cnv_pon.hdf5
SNP_SITES=common_snps.vcf
TUMOR=$1
NORMAL=$2
OUTDIR=$3

mkdir -p $OUTDIR

# Collect read counts
gatk CollectReadCounts -R $REFERENCE -I $TUMOR -L $INTERVALS \
    -O $OUTDIR/​tumor.counts.hdf5
gatk CollectReadCounts -R $REFERENCE -I $NORMAL -L $INTERVALS \
    -O $OUTDIR/​normal.counts.hdf5

# Denoise
gatk DenoiseReadCounts -I $OUTDIR/​tumor.counts.hdf5 \
    --count-panel-of-normals $PON \
    --standardized-copy-ratios $OUTDIR/​tumor.standardized.tsv \
    --denoised-copy-ratios $OUTDIR/​tumor.denoised.tsv

# Allelic counts
gatk CollectAllelicCounts -R $REFERENCE -I $TUMOR -L $SNP_SITES \
    -O $OUTDIR/​tumor.allelicCounts.tsv
gatk CollectAllelicCounts -R $REFERENCE -I $NORMAL -L $SNP_SITES \
    -O $OUTDIR/​normal.allelicCounts.tsv

# Model and call
gatk ModelSegments \
    --denoised-copy-ratios $OUTDIR/​tumor.denoised.tsv \
    --allelic-counts $OUTDIR/​tumor.allelicCounts.tsv \
    --normal-allelic-counts $OUTDIR/​normal.allelicCounts.tsv \
    --output-prefix tumor -O $OUTDIR/

gatk CallCopyRatioSegments -I $OUTDIR/​tumor.cr.seg -O $OUTDIR/​tumor.called.seg

Key Output Files

Related Skills

• copy-number/​cnvkit-analysis - Alternative CNV caller
• copy-number/​cnv-visualization - Plotting results
• alignment-files/​bam-statistics - Input BAM QC
• variant-calling/​variant-calling - SNP calling for allelic counts