gwas-database

What this skill does

# 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):**
```
rs7903146
```
Returns all trait associations for this SNP.

**By Disease/Trait:**
```
type 2 diabetes
Parkinson disease
body mass index
```
Returns all associated genetic variants.

**By Gene:**
```
APOE
TCF7L2
```
Returns variants in or near the gene region.

**By Chromosomal Region:**
```
10:114000000-115000000
```
Returns variants in the specified genomic interval.

**By Publication:**
```
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:**

1. **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()
   ```

2. **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()
   ```

3. **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()
   ```

4. **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:**
1. **FTP download**: http://ftp.ebi.ac.uk/pub/databases/gwas/summary_statistics/
2. **REST API**: Query-based access to summary statistics
3. **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-st