Preparing the Input Data¶

Config file¶

The config file is in YAML format. It is composed of general and module-specific parameters. In YAML, a variable can be of the following types: boolean, string, numeric, list and dictionary. They are declared by writing the variable name followed by a colon, a space, and the value, for example:

# A boolean is binary and can be true of false
boolean_var: true    # or false

# A string is a text. Quotation marks are not needed.
string_var: whatever text

# A numeric can be an integer or a real number. A dot separates a decimal.
numeric_var: 0.05

# A list is a collection of elements of the same type.
list_var:
  - element_1   # elements are indented
  - element_2

# A dictionary contains key-value pairs. It is a collection of multiple
#    elements where the key is a string and the value any type.
dictionary_var:
  key_1: value_1
  key_2: value_2

Now we describe the different parameters needed in DROP.

Global parameters¶

Parameter	Type	Description	Default/Examples
projectTitle	character	Title of the project to be displayed on the rendered HTML output	`Project 1`
htmlOutputPath	character	Full path of the folder where the HTML files are rendered	`/data/project1/htmlOutput`
indexWithFolderName	boolean	If true, the basename of the project directory will be used as prefix for the index.html file	`true`
genomeAssembly	character	Either hg19/hs37d5 or hg38/GRCh38, depending on the genome assembly used for mapping	`/data/project1`
sampleAnnotation	character	Full path of the sample annotation table	`/data/project1/sample_annotation.tsv`
root	character	Full path of the folder where the subdirectories processed_data and processed_results will be created containing DROP’s output files.	`/data/project1`
geneAnnotation	dictionary	A key-value list of the annotation name (key) and the full path to the GTF file (value). More than one annotation file can be provided.	`anno1: /path/to/gtf1.gtf` `anno2: /path/to/gtf2.gtf`
hpoFile	character	Full path of the file containing HPO terms. If `null` (default), it reads it from our webserver. Refer to Files to download.	`/path/to/hpo_file.tsv`
tools	dictionary	A key-value list of different commands (key) and the command (value) to run them	`gatkCmd: gatk` `bcftoolsCmd: bcftools` `samtoolsCmd: samtools`

Export counts dictionary¶

Parameter	Type	Description	Default/Examples
geneAnnotations	list	key(s) from the `geneAnnotation` parameter, whose counts should be exported	`- gencode34`
excludeGroups	list	aberrant expression and aberrant splicing groups whose counts should not be exported. If `null` all groups are exported.	`- group1`

Aberrant expression dictionary¶

Parameter	Type	Description	Default/Examples
groups	list	DROP groups that should be executed in this module. If not specified or `null` all groups are used.	`- group1` `- group2`
minIds	numeric	A positive number indicating the minimum number of samples that a group needs in order to be analyzed. We recommend at least 50.	`1`
fpkmCutoff	numeric	A positive number indicating the minimum FPKM 5% of the samples per gene should have. If a gene has less it will be filtered out.	`1 # suggested by OUTRIDER`
implementation	character	Either ‘autoencoder’, ‘pca’ or ‘peer’. Methods to remove sample covariation in OUTRIDER.	`autoencoder`
zScoreCutoff	numeric	A non-negative number. Z scores (in absolute value) greater than this cutoff are considered as outliers.	`0`
padjCutoff	numeric	A number between (0, 1] indicating the maximum FDR an event can have in order to be considered an outlier.	`0.05`
maxTestedDimensionProportion	numeric	An integer that controls the maximum value that the encoding dimension can take. Refer to Advanced options.	`3`

Aberrant splicing dictionary¶

Parameter	Type	Description	Default/Examples
groups	list	Same as in aberrant expression.	`# see aberrant expression example`
minIds	numeric	Same as in aberrant expression.	`1`
recount	boolean	If true, it forces samples to be recounted.	`false`
longRead	boolean	Set to true only if counting Nanopore or PacBio long reads.	`false`
keepNonStandardChrs	boolean	Set to true if non standard chromosomes are to be kept for further analysis.	`true`
filter	boolean	If false, no filter is applied. We recommend filtering.	`true`
minExpressionInOneSample	numeric	The minimal read count in at least one sample required for an intron to pass the filter.	`20`
minDeltaPsi	numeric	The minimal variation (in delta psi) required for an intron to pass the filter.	`0.05`
implementation	character	Either ‘PCA’ or ‘PCA-BB-Decoder’. Methods to remove sample covariation in FRASER.	`PCA`
deltaPsiCutoff	numeric	A non-negative number. Delta psi values greater than this cutoff are considered as outliers.	`0.3 # suggested by FRASER`
padjCutoff	numeric	Same as in aberrant expression.	`0.1`
maxTestedDimensionProportion	numeric	Same as in aberrant expression.	`6`

Mono-allelic expression dictionary¶

Parameter	Type	Description	Default/Examples
groups	list	Same as in aberrant expression.	`# see aberrant expression example`
genome	character	Full path of a human reference genome fasta file	`/path/to/hg19.fa`
gatkIgnoreHeaderCheck	boolean	If true (recommended), it ignores the header warnings of a VCF file when performing the allelic counts	`true`
padjCutoff	numeric	Same as in aberrant expression.	`0.05`
allelicRatioCutoff	numeric	A number between [0.5, 1) indicating the maximum allelic ratio allele1/(allele1+allele2) for the test to be significant.	`0.8`
addAF	boolean	Whether or not to add the allele frequencies from gnomAD	`true`
maxAF	numeric	Maximum allele frequency (of the minor allele) cut-off. Variants with AF equal or below this number are considered rare.	`0.001`
maxVarFreqCohort	numeric	Maximum variant frequency among the cohort.	`0.05`
qcVcf	character	Full path to the vcf file used for VCF-BAM matching. Refer to Files to download.	`/path/to/qc_vcf.vcf.gz`
qcGroups	list	Same as “groups”, but for the VCF-BAM matching	`# see aberrant expression example`

Creating the sample annotation table¶

For a detailed explanation of the columns of the sample annotation, please refer to the DROP manuscript. Inside the sample annotation, each row corresponds to a unique pair of RNA and DNA samples derived from the same individual. An RNA assay can belong to one or more DNA assays, and vice-versa. If so, they must be specified in different rows. The required columns are RNA_ID, RNA_BAM_FILE and DROP_GROUP, plus other module-specific ones (see DROP manuscript). In case external counts are included, add a new row for each sample from those files (or a subset if not all samples are needed).

The sample annotation file should be saved in the tab-separated values (tsv) format. The column order does not matter. Also, it does not matter where it is stored, as the path is specified in the config file. Here we provide some examples on how to deal with certain situations. For simplicity, we do not include all possible columns in the examples.

Example of RNA replicates¶

RNA_ID	DNA_ID	DROP_GROUP	RNA_BAM_FILE	DNA_VCF_FILE
S10R_B	S10G	BLOOD	/path/to/S10R_B.BAM	/path/to/S10G.vcf.gz
S10R_M	S10G	MUSCLE	/path/to/S10R_M.BAM	/path/to/S10G.vcf.gz

Example of DNA replicates¶

RNA_ID	DNA_ID	DROP_GROUP	RNA_BAM_FILE	DNA_VCF_FILE
S20R	S20E	WES	/path/to/S20R.BAM	/path/to/S20E.vcf.gz
S20R	S20G	WGS	/path/to/S20R.BAM	/path/to/S20G.vcf.gz

Example of a multi-sample vcf file¶

RNA_ID	DNA_ID	DROP_GROUP	RNA_BAM_FILE	DNA_VCF_FILE
S10R	S10G	WGS	/path/to/S10R.BAM	/path/to/multi_sample.vcf.gz
S20R	S20G	WGS	/path/to/S20R.BAM	/path/to/multi_sample.vcf.gz

External count matrices¶

In case counts from external matrices are to be integrated into the analysis, the file must be specified in the GENE_COUNTS_FILE column. A new row must be added for each sample from the count matrix that should be included in the analysis. An RNA_BAM_FILE must not be specified. The DROP_GROUP of the local and external samples that are to be analyzed together must be the same. Similarly, the GENE_ANNOTATION of the external counts and the key of the geneAnnotation parameter from the config file must match.

RNA_ID	DNA_ID	DROP_GROUP	RNA_BAM_FILE	GENE_COUNTS_FILE	GENE_ANNOTATION
S10R	S10G	BLOOD	/path/to/S10R.BAM
EXT-1R		BLOOD		/path/to/externalCounts.tsv.gz	gencode34
EXT-2R		BLOOD		/path/to/externalCounts.tsv.gz	gencode34

Files to download¶

Two different files can be downloaded from our public repository.

1. VCF file containing different positions to be used to match DNA with RNA files. The file name is qc_vcf_1000G_{genome_build}.vcf.gz. One file is available for each genome build (hg19/hs37d5 and hg38/GRCh38). Download it together with the corresponding .tbi file. Indicate the full path to the vcf file in the qcVcf key in the mono-allelic expression dictionary. This file is only needed for the MAE module. Otherwise, write null in the qcVcf key.

2. Text file containing the relations between genes and phenotypes encoded as HPO terms. The file name is hpo_genes.tsv.gz. Download it and indicate the full path to it in the hpoFile key. The file is only needed in case HPO terms are specified in the sample annotation. Otherwise, write null in the hpoFile key.

Advanced options¶

A local copy of DROP can be edited and modified for uncovering potential issues or increasing outputs. For example, the user might want to add new plots to the Summary scripts, or add additional columns to the results tables. Specifically, the number of threads allowed for a computational step can be modified by the user.

Note

DROP needs to be installed from a local directory Other DROP versions using pip install -e <path/to/drop-repo> so that any changes in the code will be available in the next pipeline run. Any changes made to the R code need to be updated with drop update in the project directory.

The aberrant expression and splicing modules use a denoising autoencoder to correct for sample covariation. This process reduces the fitting space to a dimension smaller than the number of samples N. The encoding dimension is optimized. We recommend the search space to be at most N/3 for the aberrant expression, and N/6 for the aberrant splicing case. Nevertheless, the user can specify the denominator with the parameter maxTestedDimensionProportion.