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SNPs from the GWAS catalog as a LOLA region set
SNPs from the GWAS catalog as a LOLA region set

{% include JB/setup %}

Ever wondered if some genomic regions of interest overlap significantly with known (or own) sets of regions?

LOLA is an R package that handles that for you. It includes a "core" set of regions from public databases and lets you extend them with your own regions of interest.

I wanted to include the position of every known SNP associated with a trait (specially clinical) in the database, but also preferebly grouped by the broad type of trait. here's what I came up with by using EBI's GWAS catalog.

Creating a bed file with SNPs for each disease group

{% highlight python %}

import os import pandas as pd import re

get GWAS catalog

os.system("wget -O gwas_catalog.tsv") # gwas db dump os.system("wget") # gwas mapping/ontology

read in catalog and mappings

df = pd.read_csv("gwas_catalog.tsv", sep="\t") mapping = pd.read_excel("GWAS-EFO-Mappings201405.xlsx")

merge both

df2 = pd.merge(df, mapping, on=['PUBMEDID'])

subset columns

df3 = df2[['CHR_ID', 'CHR_POS', 'PUBMEDID', 'DISEASE/TRAIT', 'PARENT', 'SNPS', 'STRONGEST SNP-RISK ALLELE', 'P-VALUE', 'OR or BETA']] df3.columns = ['chr', 'pos', 'pubmed_id', 'trait', 'ontology_group', 'snp', 'snp_strongest_allele', 'p_value', 'beta'] df3.to_csv("gwas_catalog.csv", index=False)

filter on p-value

df4 = df3[df3['p_value'] < 5e-8]

if not os.path.exists("regions"): os.makedirs("regions")

export bed file for each ontology group

regionset_index = pd.DataFrame() for group in df4['ontology_group'].unique(): df5 = df4[df4['ontology_group'] == group] df5 = df5[['chr', 'pos']] df5.columns = ['chr', 'start'] # drop entries without a position df5.dropna(how='any', subset=['chr', 'start'], inplace=True) df5['chr'] = ['chr' + str(int(i)) for i in df5['chr']] df5['end'] = df5['start'] + 1

df5['start'] = df5['start'].astype(int)
df5['end'] = df5['end'].astype(int)

# write bed file
group = re.sub(" ", "_", group).lower()
df5.drop_duplicates().to_csv("regions/gwas_catalog.%s.bed" % group, sep="\t", header=False, index=False)

# save in regionset index
regionset_index = regionset_index.append(pd.Series(["Human", "SNPs in gwas catalog - %s" % group, "GWAS catalog", "gwas_catalog.%s.bed" % group]), ignore_index=True)

save regionset index

regionset_index.columns = ["species", "description", "dataSource", "filename"] regionset_index.to_csv("index.txt", sep="\t", index=False)

{% endhighlight %}

You will have a file named index.txt enumerating the various region sets, which are inside a folder named regions.

Documenting your region sets

Simply create a tab-delimited file in the same folder named collection.txt with the following information:

collector date source description
arendeiro 2016-01-28 customRegionDB/hg38/gwas GWAS from EBI's GWAS catalog (