---
title: "gwascat: structuring and querying the NHGRI GWAS catalog"
author: "Vincent J. Carey, stvjc at channing.harvard.edu"
date: "`r format(Sys.time(), '%B %d, %Y')`"
vignette: >
  %\VignetteEngine{knitr::rmarkdown}
  %\VignetteIndexEntry{gwascat: structuring and querying the NHGRI GWAS catalog}
  %\VignetteEncoding{UTF-8}
output:
  BiocStyle::html_document:
    highlight: pygments
    number_sections: yes
    theme: united
    toc: yes
bibliography: gwascat.bib
---


# Introduction

NHGRI maintains and routinely updates a database of selected genome-wide
association studies.  This document describes R/Bioconductor facilities for
working with contents of this database.

## Installation
The package can be installed using Bioconductor's \textit{BiocManager}
package, with the sequence
\begin{verbatim}
library(BiocManager)
BiocManager::install("gwascat")
\end{verbatim}

## Attachment and access to documentation
Once the package has been installed, use \verb+library(gwascat)+ to 
obtain interactive access to all the facilities.  After executing
this command, use \verb+help(package="gwascat")+ to obtain an overview.
The current version of this vignette can always be accessed at
www.bioconductor.org, or by suitably navigating the web pages generated
with \texttt{help.start()}.

```{r getlib,echo=FALSE,results='hide'}
library(gwascat)
```

## Getting a recent version of the GWAS catalog

We use BiocFileCache to manage downloaded TSV from
EBI's download site.  The file is provided without
compression, so prepare for 100+MB download if you
are not working from a cache.  There is no etag
set, so you have to check for updates on your own.

```{r lkadasd}
args(get_cached_gwascat)
```

This is converted to a manageable extension of GRanges using
`process_gwas_dataframe`.
```{r lkasdasdasd}
args(process_gwas_dataframe)
```


# Illustrations: computing

```{r lk1,echo=FALSE,results='hide'}
if (length(grep("gwascat", search()))>0) detach("package:gwascat")
```
Available functions are:
```{r lk2}
library(gwascat)
objects("package:gwascat")
```

An extended GRanges instance with a sample of 50000 SNP-disease associations reported
on 30 April 2020 is
obtained as follows, with addresses based on the GRCh38 genome build.
We use `gwtrunc` to refer to it in the sequel.
```{r lkgr}
data(ebicat_2020_04_30)
gwtrunc = ebicat_2020_04_30
```

To determine the most frequently occurring traits in this sample:
```{r lktr}
topTraits(gwtrunc)
```

For a given trait, obtain a GRanges with all recorded associations; here
only three associations are shown:
```{r lklocs}
subsetByTraits(gwtrunc, tr="LDL cholesterol")[1:3]
```

# Some visualizations

## Basic Manhattan plot

A basic Manhattan plot is easily constructed with the
ggbio package facilities.  Here we confine attention to
chromosomes 4:6.  First, we create a version of the
catalog with $-log_{10} p$ truncated at a maximum value of 25.

```{r lkm,results='hide'}
requireNamespace("S4Vectors")
mcols = S4Vectors::mcols
mlpv = mcols(gwtrunc)$PVALUE_MLOG
mlpv = ifelse(mlpv > 25, 25, mlpv)
S4Vectors::mcols(gwtrunc)$PVALUE_MLOG = mlpv
library(GenomeInfoDb)
# seqlevelsStyle(gwtrunc) = "UCSC" # no more!
seqlevels(gwtrunc) = paste0("chr", seqlevels(gwtrunc))
gwlit = gwtrunc[ which(as.character(seqnames(gwtrunc)) %in% c("chr4", "chr5", "chr6")) ]
library(ggbio)
mlpv = mcols(gwlit)$PVALUE_MLOG
mlpv = ifelse(mlpv > 25, 25, mlpv)
S4Vectors::mcols(gwlit)$PVALUE_MLOG = mlpv
```{r dorunap}
autoplot(gwlit, geom="point", aes(y=PVALUE_MLOG), xlab="chr4-chr6")
```

\setkeys{Gin}{width=0.95\textwidth}
\includegraphics{litman}

## Annotated Manhattan plot

A simple call permits visualization of GWAS results for
a small number of traits.  Note the defaults in this call.

```{r runit,eval=TRUE}
traitsManh(gwtrunc)
```

%\setkeys{Gin}{width=0.95\textwidth}
%\includegraphics{annman}

## Integrative view of potential genetic determinants


The following chunk uses GFF3 data on eQTL and related
phenomena distributed at the GBrowse instance at
eqtl.uchicago.edu.  A request for all information at
43-45 Mb was made on 2 June 2012, yielding the GFF3 referenced below.
Of interest are locations and
scores of genetic associations with DNaseI hypersensitivity
(scores identifying dsQTL, see Degner et al 2012).
```{r getgd}
gffpath = system.file("gff3/chr17_43000000_45000000.gff3", package="gwascat")
library(rtracklayer)
c17tg = import(gffpath)
```

We make a Gviz DataTrack of the dsQTL scores.
```{r lkgvt}
c17td = c17tg[ which(S4Vectors::mcols(c17tg)$type == "Degner_dsQTL") ]
library(Gviz)
dsqs = DataTrack( c17td, chrom="chr17", genome="hg19", data="score",
  name="dsQTL")
```

We start the construction of the graph here.
```{r dost}
g2 = GRanges(seqnames="chr17", IRanges(start=4.3e7, width=2e6))

basic = gwcex2gviz(basegr = gwtrunc, contextGR=g2, plot.it=FALSE) 
```

We also collect locations of eQTL in the Stranger 2007
multipopulation eQTL study.
```{r getstr}
c17ts = c17tg[ which(S4Vectors::mcols(c17tg)$type == "Stranger_eqtl") ]
eqloc = AnnotationTrack(c17ts,  chrom="chr17", genome="hg19", name="Str eQTL")
displayPars(eqloc)$col = "black"
displayPars(dsqs)$col = "red"
integ = list(basic[[1]], eqloc, dsqs, basic[[2]], basic[[3]])
```

Now use Gviz.

```{r doplot}
plotTracks(integ)
```

# SNP sets and trait sets

## SNPs by name

We can regard the content of a SNP chip as a set of SNP, referenced
by name.  The
pd.genomewidesnp.6 package describes the Affymetrix SNP 6.0 chip.
We can determine which traits are associated with loci interrogated
by the chip as follows.  We work with a subset of the 1 million loci
for illustration.

The \texttt{locon6} data frame has information on 10000 probes,
acquired through the following code (not executed here to reduce
dependence on the pd.genomewidesnp.6 package, which is very large.
```{r dobig,eval=FALSE}
library(pd.genomewidesnp.6)
con = pd.genomewidesnp.6@getdb()
locon6 = dbGetQuery(con, 
   "select dbsnp_rs_id, chrom, physical_pos from featureSet limit 10000")
```
Instead use the serialized information:
```{r doloc}
data(locon6)
rson6 = as.character(locon6[[1]])
rson6[1:5]
```

We subset the GWAS ranges structure with rsids that
are common to both the chip and the GWAS catalog.
We then tabulate the diseases associated with the
common loci.
```{r lkdtab}
intr = gwtrunc[ intersect(getRsids(gwtrunc), rson6) ]
sort(table(getTraits(intr)), decreasing=TRUE)[1:10]
```

## Traits by genomic location

We will assemble genomic coordinates for SNP on the Affymetrix 6.0 chip
and show the effects of identifying the trait-associated
loci with regions of width 1000bp instead
of 1bp.

The following code retrieves coordinates for SNP interrogated
on 10000 probes (to save time)
on the 6.0 chip, in a GRanges instance that was lifted over to GRCh38.
The data statement is preceded by legacy code that produced
an instance with hg19 coordinates.
```{r lkexp,keep.source=TRUE}
#gr6.0 = GRanges(seqnames=ifelse(is.na(locon6$chrom),0,locon6$chrom), 
#       IRanges(ifelse(is.na(locon6$phys),1,locon6$phys), width=1))
#S4Vectors::mcols(gr6.0)$rsid = as.character(locon6$dbsnp_rs_id)
#seqlevels(gr6.0) = paste("chr", seqlevels(gr6.0), sep="")
data(gr6.0_hg38)
```

Here we compute overlaps with both the raw disease-associated locus
addresses, and with the locus address $\pm$ 500bp.
```{r dosub}
ag = function(x) as(x, "GRanges")
ovraw = suppressWarnings(subsetByOverlaps(ag(gwtrunc), gr6.0_hg38))
length(ovraw)
ovaug = suppressWarnings(subsetByOverlaps(ag(gwtrunc+500), gr6.0_hg38))
length(ovaug)
```

To acquire the subset of the catalog to which 6.0 probes are
within 500bp, use:
```{r dosub2}
rawrs = mcols(ovraw)$SNPS
augrs = mcols(ovaug)$SNPS
gwtrunc[augrs]
```

Relaxing the intersection criterion in this
limited case leads to a larger set of traits.

```{r lkrelax}
nn = setdiff( getTraits(gwtrunc[augrs]), getTraits(gwtrunc[rawrs]) )
length(nn)
head(nn)
tail(nn)
```

# Counting alleles associated with traits

We can use \texttt{riskyAlleleCount} to count
risky alleles enumerated in the GWAS catalog.  This
particular function assumes that we have genotyped at
the catalogued loci.  Below we will discuss how to impute
from non-catalogued loci to those enumerated in the catalog.
```{r lkcout}
data(gg17N) # translated from GGdata chr 17 calls using ABmat2nuc
gg17N[1:5,1:5]
```
This function can use genotype information in the A/B format,
assuming that B denotes the alphabetically later nucleotide.
Because we have direct nucleotide coding in our matrix, we set
the \texttt{matIsAB} parameter to false in this call.

```{r dorun}
h17 = riskyAlleleCount(gg17N, matIsAB=FALSE, chr="ch17",
 gwwl = gwtrunc)
h17[1:5,1:5]
table(as.numeric(h17))
```

It is of interest to bind the counts back to the catalog data.
```{r domo}
gwr = gwtrunc
gwr = gwr[colnames(h17),]
S4Vectors::mcols(gwr) = cbind(mcols(gwr), DataFrame(t(h17)))
sn = rownames(h17)
gwr[,c("DISEASE/TRAIT", sn[1:4])]
```

Now by programming on the metadata columns, we can identify
individuals with particular risk profiles.

# Formal management of trait vocabularies

## Diseases: Disease Ontology

The Disease Ontology project @Osborne:2009p4571 formalizes a vocabulary
for human diseases.  Bioconductor's DO.db package is a curated
representation.

```{r getdo}
library(DO.db)
DO()
```

All tokens of the ontology are acquired via:
```{r getallt}
alltob = unlist(mget(mappedkeys(DOTERM), DOTERM))
allt = sapply(alltob, Term)
allt[1:5]
```

Direct mapping from disease trait tokens in the catalog
to this vocabulary succeeds for a modest proportion of
records.
```{r dohit}
cattra = mcols(gwtrunc)$`DISEASE/TRAIT`
mat = match(tolower(cattra), tolower(allt))
catDO = names(allt)[mat]
na.omit(catDO)[1:50]
mean(is.na(catDO))
```

Approximate matching of unmatched tokens can proceed
by various routes.  Some traits are not diseases, and
will not be mappable using Disease Ontology.  However, consider
```{r dogr}
unique(cattra[is.na(catDO)])[1:20]
nomatch = cattra[is.na(catDO)]
unique(nomatch)[1:5]
```
Manual searching shows that a number of these have
very close matches.

## Other phenotypic traits: Human Phenotype Ontology

Bioconductor does not possess an annotation package for phenotype ontology,
but the standardized OBO format can be parsed and modeled into a graph.

```{r dopar,cache=FALSE}
hpobo = gzfile(dir(system.file("obo", package="gwascat"), pattern="hpo", full=TRUE))
HPOgraph = obo2graphNEL(hpobo)
close(hpobo)
```

The phenotypic terms are obtained via:
```{r dohpot}
requireNamespace("graph")
hpoterms = unlist(graph::nodeData(HPOgraph, graph::nodes(HPOgraph), "name"))
hpoterms[1:10]
```

Exact hits to unmatched GWAS catalog traits exist:
```{r lkint}
intersect(tolower(nomatch), tolower(hpoterms))
```

More work on formalization of trait terms is underway.

%## {Curation of approximate matches}

% NB the graph stuff can be used for other OBO without .db packages..
%The \textit{gwascat} package includes an OBO-formatted
%image of the ontology and a model for it as a \texttt{graphNEL} instance
%as defined in the Bioconductor \textit{graph} package \cite{carey2005}.

%The graph model is constructed as follows.
%<<dogrmod}
%doobo = dir(system.file("obo", package="gwascat"), full=TRUE, patt="HumanDO")
%DOgraph = obo2graphNEL(doobo)
%DOgraph
%@
%
%Nodes are the formal disease term identifiers; node data provides additional
%metadata.
%<<lkno}
%nodeData(DOgraph)[1:5]
%@

# CADD scores

@Kircher:2014p5681 define combined annotation-dependent
depletion scores measuring variant pathogenicity in an integrative way.
Small requests to bind scores for SNV to GRanges can be resolved
through HTTP; large requests can be carried out on a local tabix-indexed
selection from their archive.

```{r chkcadd,eval=FALSE}
g3 = as(gwtrunc, "GRanges")
bg3 = bindcadd_snv( g3[which(seqnames(g3)=="chr3")][1:20] )
inds = ncol(mcols(bg3))
bg3[, (inds-3):inds]
```

This requires cooperation of network interface and server, so we
don't evaluate in vignette build but on 1 Apr 2014 the response was:
```
GRanges with 20 ranges and 4 metadata columns:
       seqnames                 ranges strand   |         Ref         Alt
          <Rle>              <IRanges>  <Rle>   | <character> <character>
   [1]        3 [109789570, 109789570]      *   |           A           G
   [2]        3 [ 25922285,  25922285]      *   |           G           A
   [3]        3 [109529550, 109529550]      *   |           T           C
   [4]        3 [175055759, 175055759]      *   |           T           G
   [5]        3 [191912870, 191912870]      *   |           C           T
   ...      ...                    ...    ... ...         ...         ...
  [16]        3 [187716886, 187716886]      *   |           A           G
  [17]        3 [160820524, 160820524]      *   |           G           C
  [18]        3 [169518455, 169518455]      *   |           T           C
  [19]        3 [179172979, 179172979]      *   |           G           T
  [20]        3 [171785168, 171785168]      *   |           G           C
          CScore     PHRED
       <numeric> <numeric>
   [1] -0.182763     3.110
   [2] -0.289708     2.616
   [3]  0.225373     5.216
   [4] -0.205689     3.003
   [5] -0.172189     3.161
   ...       ...       ...
  [16] -0.019710     3.913
  [17] -0.375183     2.235
  [18] -0.695270     0.987
  [19] -0.441673     1.949
  [20]  0.231972     5.252
  ---
  seqlengths:
           1         2         3         4 ...        21        22         X
   249250621 243199373 198022430 191154276 ...  48129895  51304566 155270560
```

# Appendix: Adequacy of location annotation

A basic question concerning the use of archived
SNP identifiers is durability
of the association between asserted location
and SNP identifier.  The \texttt{chklocs}
function uses a current Bioconductor
SNPlocs package to check this.

For example, to verify that locations asserted on chromosome
20 agree between the Bioconductor dbSNP image and the
gwas catalog,
```{r getrs,keep.source=TRUE,cache=FALSE,eval=FALSE}
if ("SNPlocs.Hsapiens.dbSNP144.GRCh37" %in% installed.packages()[,1]) {
 library(SNPlocs.Hsapiens.dbSNP144.GRCh37)
 chklocs("20", gwtrunc)
}
```
This is not a fast procedure.  

# Acknowledgment 

The development of this software was supported in part
by Robert Gentleman and the
Computational Biology Group of
Genentech, Inc.

# References

\bibliography{gwascat}

