GWAS Catalog Database

Overview

The GWAS Catalog is a comprehensive repository of published genome-wide association studies maintained by the National Human Genome Research Institute (NHGRI) and the European Bioinformatics Institute (EBI). The catalog contains curated SNP-trait associations from thousands of GWAS publications, including genetic variants, associated traits and diseases, p-values, effect sizes, and full summary statistics for many studies.

When to Use This Skill

This skill should be used when queries involve:

•Genetic variant associations: Finding SNPs associated with diseases or traits
•SNP lookups: Retrieving information about specific genetic variants (rs IDs)
•Trait/disease searches: Discovering genetic associations for phenotypes
•Gene associations: Finding variants in or near specific genes
•GWAS summary statistics: Accessing complete genome-wide association data
•Study metadata: Retrieving publication and cohort information
•Population genetics: Exploring ancestry-specific associations
•Polygenic risk scores: Identifying variants for risk prediction models
•Functional genomics: Understanding variant effects and genomic context
•Systematic reviews: Comprehensive literature synthesis of genetic associations

Core Capabilities

1. Understanding GWAS Catalog Data Structure

The GWAS Catalog is organized around four core entities:

•Studies: GWAS publications with metadata (PMID, author, cohort details)
•Associations: SNP-trait associations with statistical evidence (p ≤ 5×10⁻⁸)
•Variants: Genetic markers (SNPs) with genomic coordinates and alleles
•Traits: Phenotypes and diseases (mapped to EFO ontology terms)

Key Identifiers:

•Study accessions: GCST IDs (e.g., GCST001234)
•Variant IDs: rs numbers (e.g., rs7903146) or variant_id format
•Trait IDs: EFO terms (e.g., EFO_0001360 for type 2 diabetes)
•Gene symbols: HGNC approved names (e.g., TCF7L2)

2. Web Interface Searches

The web interface at https://www.ebi.ac.uk/gwas/ supports multiple search modes:

By Variant (rs ID):

code

rs7903146

Returns all trait associations for this SNP.

By Disease/Trait:

code

type 2 diabetes
Parkinson disease
body mass index

Returns all associated genetic variants.

By Gene:

code

APOE
TCF7L2

Returns variants in or near the gene region.

By Chromosomal Region:

code

10:114000000-115000000

Returns variants in the specified genomic interval.

By Publication:

code

PMID:20581827
Author: McCarthy MI
GCST001234

Returns study details and all reported associations.

3. REST API Access

The GWAS Catalog provides two REST APIs for programmatic access:

Base URLs:

•GWAS Catalog API: https://www.ebi.ac.uk/gwas/rest/api
•Summary Statistics API: https://www.ebi.ac.uk/gwas/summary-statistics/api

API Documentation:

•Main API docs: https://www.ebi.ac.uk/gwas/rest/docs/api
•Summary stats docs: https://www.ebi.ac.uk/gwas/summary-statistics/docs/

Core Endpoints:

•

Studies endpoint - /studies/{accessionID}

python

import requests

# Get a specific study
url = "https://www.ebi.ac.uk/gwas/rest/api/studies/GCST001795"
response = requests.get(url, headers={"Content-Type": "application/json"})
study = response.json()

•

Associations endpoint - /associations

python

# Find associations for a variant
variant = "rs7903146"
url = f"https://www.ebi.ac.uk/gwas/rest/api/singleNucleotidePolymorphisms/{variant}/associations"
params = {"projection": "associationBySnp"}
response = requests.get(url, params=params, headers={"Content-Type": "application/json"})
associations = response.json()

•

Variants endpoint - /singleNucleotidePolymorphisms/{rsID}

python

# Get variant details
url = "https://www.ebi.ac.uk/gwas/rest/api/singleNucleotidePolymorphisms/rs7903146"
response = requests.get(url, headers={"Content-Type": "application/json"})
variant_info = response.json()

•

Traits endpoint - /efoTraits/{efoID}

python

# Get trait information
url = "https://www.ebi.ac.uk/gwas/rest/api/efoTraits/EFO_0001360"
response = requests.get(url, headers={"Content-Type": "application/json"})
trait_info = response.json()

4. Query Examples and Patterns

Example 1: Find all associations for a disease

python

import requests

trait = "EFO_0001360"  # Type 2 diabetes
base_url = "https://www.ebi.ac.uk/gwas/rest/api"

# Query associations for this trait
url = f"{base_url}/efoTraits/{trait}/associations"
response = requests.get(url, headers={"Content-Type": "application/json"})
associations = response.json()

# Process results
for assoc in associations.get('_embedded', {}).get('associations', []):
    variant = assoc.get('rsId')
    pvalue = assoc.get('pvalue')
    risk_allele = assoc.get('strongestAllele')
    print(f"{variant}: p={pvalue}, risk allele={risk_allele}")

Example 2: Get variant information and all trait associations

python

import requests

variant = "rs7903146"
base_url = "https://www.ebi.ac.uk/gwas/rest/api"

# Get variant details
url = f"{base_url}/singleNucleotidePolymorphisms/{variant}"
response = requests.get(url, headers={"Content-Type": "application/json"})
variant_data = response.json()

# Get all associations for this variant
url = f"{base_url}/singleNucleotidePolymorphisms/{variant}/associations"
params = {"projection": "associationBySnp"}
response = requests.get(url, params=params, headers={"Content-Type": "application/json"})
associations = response.json()

# Extract trait names and p-values
for assoc in associations.get('_embedded', {}).get('associations', []):
    trait = assoc.get('efoTrait')
    pvalue = assoc.get('pvalue')
    print(f"Trait: {trait}, p-value: {pvalue}")

Example 3: Access summary statistics

python

import requests

# Query summary statistics API
base_url = "https://www.ebi.ac.uk/gwas/summary-statistics/api"

# Find associations by trait with p-value threshold
trait = "EFO_0001360"  # Type 2 diabetes
p_upper = "0.000000001"  # p < 1e-9
url = f"{base_url}/traits/{trait}/associations"
params = {
    "p_upper": p_upper,
    "size": 100  # Number of results
}
response = requests.get(url, params=params)
results = response.json()

# Process genome-wide significant hits
for hit in results.get('_embedded', {}).get('associations', []):
    variant_id = hit.get('variant_id')
    chromosome = hit.get('chromosome')
    position = hit.get('base_pair_location')
    pvalue = hit.get('p_value')
    print(f"{chromosome}:{position} ({variant_id}): p={pvalue}")

Example 4: Query by chromosomal region

python

import requests

# Find variants in a specific genomic region
chromosome = "10"
start_pos = 114000000
end_pos = 115000000

base_url = "https://www.ebi.ac.uk/gwas/rest/api"
url = f"{base_url}/singleNucleotidePolymorphisms/search/findByChromBpLocationRange"
params = {
    "chrom": chromosome,
    "bpStart": start_pos,
    "bpEnd": end_pos
}
response = requests.get(url, params=params, headers={"Content-Type": "application/json"})
variants_in_region = response.json()

5. Working with Summary Statistics

The GWAS Catalog hosts full summary statistics for many studies, providing access to all tested variants (not just genome-wide significant hits).

Access Methods:

•FTP download: http://ftp.ebi.ac.uk/pub/databases/gwas/summary_statistics/
•REST API: Query-based access to summary statistics
•Web interface: Browse and download via the website

Summary Statistics API Features:

•Filter by chromosome, position, p-value
•Query specific variants across studies
•Retrieve effect sizes and allele frequencies
•Access harmonized and standardized data

Example: Download summary statistics for a study

python

import requests
import gzip

# Get available summary statistics
base_url = "https://www.ebi.ac.uk/gwas/summary-statistics/api"
url = f"{base_url}/studies/GCST001234"
response = requests.get(url)
study_info = response.json()

# Download link is provided in the response
# Alternatively, use FTP:
# ftp://ftp.ebi.ac.uk/pub/databases/gwas/summary_statistics/GCSTXXXXXX/

6. Data Integration and Cross-referencing

The GWAS Catalog provides links to external resources:

Genomic Databases:

•Ensembl: Gene annotations and variant consequences
•dbSNP: Variant identifiers and population frequencies
•gnomAD: Population allele frequencies

Functional Resources:

•Open Targets: Target-disease associations
•PGS Catalog: Polygenic risk scores
•UCSC Genome Browser: Genomic context

Phenotype Resources:

•EFO (Experimental Factor Ontology): Standardized trait terms
•OMIM: Disease gene relationships
•Disease Ontology: Disease hierarchies

Following Links in API Responses:

python

import requests

# API responses include _links for related resources
response = requests.get("https://www.ebi.ac.uk/gwas/rest/api/studies/GCST001234")
study = response.json()

# Follow link to associations
associations_url = study['_links']['associations']['href']
associations_response = requests.get(associations_url)

Query Workflows

Workflow 1: Exploring Genetic Associations for a Disease

•
Identify the trait using EFO terms or free text:
- •Search web interface for disease name
- •Note the EFO ID (e.g., EFO_0001360 for type 2 diabetes)

•

Query associations via API:

python

url = f"https://www.ebi.ac.uk/gwas/rest/api/efoTraits/{efo_id}/associations"

•
Filter by significance and population:
- •Check p-values (genome-wide significant: p ≤ 5×10⁻⁸)
- •Review ancestry information in study metadata
- •Filter by sample size or discovery/replication status
•
Extract variant details:
- •rs IDs for each association
- •Effect alleles and directions
- •Effect sizes (odds ratios, beta coefficients)
- •Population allele frequencies
•
Cross-reference with other databases:
- •Look up variant consequences in Ensembl
- •Check population frequencies in gnomAD
- •Explore gene function and pathways

Workflow 2: Investigating a Specific Genetic Variant

•

Query the variant:

python

url = f"https://www.ebi.ac.uk/gwas/rest/api/singleNucleotidePolymorphisms/{rs_id}"

•

Retrieve all trait associations:

python

url = f"https://www.ebi.ac.uk/gwas/rest/api/singleNucleotidePolymorphisms/{rs_id}/associations"

•
Analyze pleiotropy:
- •Identify all traits associated with this variant
- •Review effect directions across traits
- •Look for shared biological pathways
•
Check genomic context:
- •Determine nearby genes
- •Identify if variant is in coding/regulatory regions
- •Review linkage disequilibrium with other variants

Workflow 3: Gene-Centric Association Analysis

•

Search by gene symbol in web interface or:

python

url = f"https://www.ebi.ac.uk/gwas/rest/api/singleNucleotidePolymorphisms/search/findByGene"
params = {"geneName": gene_symbol}

•
Retrieve variants in gene region:
- •Get chromosomal coordinates for gene
- •Query variants in region
- •Include promoter and regulatory regions (extend boundaries)
•
Analyze association patterns:
- •Identify traits associated with variants in this gene
- •Look for consistent associations across studies
- •Review effect sizes and directions
•
Functional interpretation:
- •Determine variant consequences (missense, regulatory, etc.)
- •Check expression QTL (eQTL) data
- •Review pathway and network context

Workflow 4: Systematic Review of Genetic Evidence

•
Define research question:
- •Specific trait or disease of interest
- •Population considerations
- •Study design requirements
•
Comprehensive variant extraction:
- •Query all associations for trait
- •Set significance threshold
- •Note discovery and replication studies
•
Quality assessment:
- •Review study sample sizes
- •Check for population diversity
- •Assess heterogeneity across studies
- •Identify potential biases
•
Data synthesis:
- •Aggregate associations across studies
- •Perform meta-analysis if applicable
- •Create summary tables
- •Generate Manhattan or forest plots
•
Export and documentation:
- •Download full association data
- •Export summary statistics if needed
- •Document search strategy and date
- •Create reproducible analysis scripts

Workflow 5: Accessing and Analyzing Summary Statistics

•
Identify studies with summary statistics:
- •Browse summary statistics portal
- •Check FTP directory listings
- •Query API for available studies

•

Download summary statistics:

bash

# Via FTP
wget ftp://ftp.ebi.ac.uk/pub/databases/gwas/summary_statistics/GCSTXXXXXX/harmonised/GCSTXXXXXX-harmonised.tsv.gz

•

Query via API for specific variants:

python

url = f"https://www.ebi.ac.uk/gwas/summary-statistics/api/chromosomes/{chrom}/associations"
params = {"start": start_pos, "end": end_pos}

•
Process and analyze:
- •Filter by p-value thresholds
- •Extract effect sizes and confidence intervals
- •Perform downstream analyses (fine-mapping, colocalization, etc.)

Response Formats and Data Fields

Key Fields in Association Records:

•rsId: Variant identifier (rs number)
•strongestAllele: Risk allele for the association
•pvalue: Association p-value
•pvalueText: P-value as text (may include inequality)
•orPerCopyNum: Odds ratio or beta coefficient
•betaNum: Effect size (for quantitative traits)
•betaUnit: Unit of measurement for beta
•range: Confidence interval
•efoTrait: Associated trait name
•mappedLabel: EFO-mapped trait term

Study Metadata Fields:

•accessionId: GCST study identifier
•pubmedId: PubMed ID
•author: First author
•publicationDate: Publication date
•ancestryInitial: Discovery population ancestry
•ancestryReplication: Replication population ancestry
•sampleSize: Total sample size

Pagination: Results are paginated (default 20 items per page). Navigate using:

•size parameter: Number of results per page
•page parameter: Page number (0-indexed)
•_links in response: URLs for next/previous pages

Best Practices

Query Strategy

•Start with web interface to identify relevant EFO terms and study accessions
•Use API for bulk data extraction and automated analyses
•Implement pagination handling for large result sets
•Cache API responses to minimize redundant requests

Data Interpretation

•Always check p-value thresholds (genome-wide: 5×10⁻⁸)
•Review ancestry information for population applicability
•Consider sample size when assessing evidence strength
•Check for replication across independent studies
•Be aware of winner's curse in effect size estimates

Rate Limiting and Ethics

•Respect API usage guidelines (no excessive requests)
•Use summary statistics downloads for genome-wide analyses
•Implement appropriate delays between API calls
•Cache results locally when performing iterative analyses
•Cite the GWAS Catalog in publications

Data Quality Considerations

•GWAS Catalog curates published associations (may contain inconsistencies)
•Effect sizes reported as published (may need harmonization)
•Some studies report conditional or joint associations
•Check for study overlap when combining results
•Be aware of ascertainment and selection biases

Python Integration Example

Complete workflow for querying and analyzing GWAS data:

python

import requests
import pandas as pd
from time import sleep

def query_gwas_catalog(trait_id, p_threshold=5e-8):
    """
    Query GWAS Catalog for trait associations

    Args:
        trait_id: EFO trait identifier (e.g., 'EFO_0001360')
        p_threshold: P-value threshold for filtering

    Returns:
        pandas DataFrame with association results
    """
    base_url = "https://www.ebi.ac.uk/gwas/rest/api"
    url = f"{base_url}/efoTraits/{trait_id}/associations"

    headers = {"Content-Type": "application/json"}
    results = []
    page = 0

    while True:
        params = {"page": page, "size": 100}
        response = requests.get(url, params=params, headers=headers)

        if response.status_code != 200:
            break

        data = response.json()
        associations = data.get('_embedded', {}).get('associations', [])

        if not associations:
            break

        for assoc in associations:
            pvalue = assoc.get('pvalue')
            if pvalue and float(pvalue) <= p_threshold:
                results.append({
                    'variant': assoc.get('rsId'),
                    'pvalue': pvalue,
                    'risk_allele': assoc.get('strongestAllele'),
                    'or_beta': assoc.get('orPerCopyNum') or assoc.get('betaNum'),
                    'trait': assoc.get('efoTrait'),
                    'pubmed_id': assoc.get('pubmedId')
                })

        page += 1
        sleep(0.1)  # Rate limiting

    return pd.DataFrame(results)

# Example usage
df = query_gwas_catalog('EFO_0001360')  # Type 2 diabetes
print(df.head())
print(f"\nTotal associations: {len(df)}")
print(f"Unique variants: {df['variant'].nunique()}")

Resources

references/api_reference.md

Comprehensive API documentation including:

•Detailed endpoint specifications for both APIs
•Complete list of query parameters and filters
•Response format specifications and field descriptions
•Advanced query examples and patterns
•Error handling and troubleshooting
•Integration with external databases

Consult this reference when:

•Constructing complex API queries
•Understanding response structures
•Implementing pagination or batch operations
•Troubleshooting API errors
•Exploring advanced filtering options

Training Materials

The GWAS Catalog team provides workshop materials:

•GitHub repository: https://github.com/EBISPOT/GWAS_Catalog-workshop
•Jupyter notebooks with example queries
•Google Colab integration for cloud execution

Important Notes

Data Updates

•The GWAS Catalog is updated regularly with new publications
•Re-run queries periodically for comprehensive coverage
•Summary statistics are added as studies release data
•EFO mappings may be updated over time

Citation Requirements

When using GWAS Catalog data, cite:

•Sollis E, et al. (2023) The NHGRI-EBI GWAS Catalog: knowledgebase and deposition resource. Nucleic Acids Research. PMID: 37953337
•Include access date and version when available
•Cite original studies when discussing specific findings

Limitations

•Not all GWAS publications are included (curation criteria apply)
•Full summary statistics available for subset of studies
•Effect sizes may require harmonization across studies
•Population diversity is growing but historically limited
•Some associations represent conditional or joint effects

Data Access

•Web interface: Free, no registration required
•REST APIs: Free, no API key needed
•FTP downloads: Open access
•Rate limiting applies to API (be respectful)

Additional Resources

•GWAS Catalog website: https://www.ebi.ac.uk/gwas/
•Documentation: https://www.ebi.ac.uk/gwas/docs
•API documentation: https://www.ebi.ac.uk/gwas/rest/docs/api
•Summary Statistics API: https://www.ebi.ac.uk/gwas/summary-statistics/docs/
•FTP site: http://ftp.ebi.ac.uk/pub/databases/gwas/
•Training materials: https://github.com/EBISPOT/GWAS_Catalog-workshop
•PGS Catalog (polygenic scores): https://www.pgscatalog.org/
•Help and support: gwas-info@ebi.ac.uk