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SKILL.md
Genomics and Epigenomics Data Processing
Production-ready computational skill for processing and analyzing epigenomics data. Combines local Python computation (pandas, scipy, numpy, pysam, statsmodels) with ToolUniverse annotation tools for regulatory context. Designed to solve BixBench-style questions about methylation, ChIP-seq, ATAC-seq, and multi-omics integration.
When to Use This Skill
Triggers:
User provides methylation data (beta-value matrices, Illumina arrays) and asks about CpG sites
Questions about differential methylation analysis
Age-related CpG detection or epigenetic clock questions
Chromosome-level methylation density or statistics
ChIP-seq peak files (BED format) with analysis questions
English-first queries - Use English in all tool calls
Complete Workflow
Phase 0: Question Parsing and Data Discovery
CRITICAL FIRST STEP: Before writing ANY code, parse the question to identify what is being asked and what data files are available.
0.1 Discover Available Data Files
import os
import glob
data_dir = "." # or specified path
all_files = glob.glob(os.path.join(data_dir, "**/*"), recursive=True)
# Categorize files
methylation_files = [f for f in all_files if any(x in f.lower() for x in
['methyl', 'beta', 'cpg', 'illumina', '450k', '850k', 'epic', 'mval'])]
chipseq_files = [f for f in all_files if any(x in f.lower() for x in
['chip', 'peak', 'narrowpeak', 'broadpeak', 'histone'])]
atacseq_files = [f for f in all_files if any(x in f.lower() for x in
['atac', 'accessibility', 'openChromatin', 'dnase'])]
bed_files = [f for f in all_files if f.endswith(('.bed', '.bed.gz', '.narrowPeak', '.broadPeak'))]
bigwig_files = [f for f in all_files if f.endswith(('.bw', '.bigwig', '.bigWig'))]
clinical_files = [f for f in all_files if any(x in f.lower() for x in
['clinical', 'patient', 'sample', 'metadata', 'phenotype', 'survival'])]
expression_files = [f for f in all_files if any(x in f.lower() for x in
['express', 'rnaseq', 'fpkm', 'tpm', 'counts', 'transcriptom'])]
manifest_files = [f for f in all_files if any(x in f.lower() for x in
['manifest', 'annotation', 'probe', 'platform'])]
# Print summary
for category, files in [
('Methylation', methylation_files),
('ChIP-seq', chipseq_files),
('ATAC-seq', atacseq_files),
('BED', bed_files),
('BigWig', bigwig_files),
('Clinical', clinical_files),
('Expression', expression_files),
('Manifest', manifest_files),
]:
if files:
print(f"{category}: {files}")
0.2 Parse Question Parameters
Extract these from the question:
Parameter
Default
Example Question Text
Significance threshold
0.05
"padj < 0.05", "FDR < 0.01"
Beta difference threshold
0
"
Variance filter
None
"variance > 0.01", "top 5000 most variable"
Chromosome filter
All
"chromosome 17", "autosomes only"
Genome build
hg38
"hg19", "GRCh37", "mm10"
CpG type filter
All
"cg probes only", "exclude ch probes"
Region filter
None
"promoter", "gene body", "intergenic"
Missing data handling
Report
"complete cases", "no missing data"
Specific comparison
Infer
"tumor vs normal", "old vs young"
Specific statistic
Infer
"density", "ratio", "count", "average"
0.3 Decision Tree
Q: What type of epigenomics data?
METHYLATION -> Phase 1 (Methylation Processing)
CHIP-SEQ -> Phase 2 (ChIP-seq Processing)
ATAC-SEQ -> Phase 3 (ATAC-seq Processing)
MULTI-OMICS -> Phase 4 (Integration)
CLINICAL -> Phase 5 (Clinical Integration)
ANNOTATION -> Phase 6 (ToolUniverse Annotation)
Q: Is this a genome-wide statistics question?
YES -> Focus on chromosome-level aggregation (Phase 7)
NO -> Focus on site/region-level analysis
Phase 1: Methylation Data Processing
1.1 Load Methylation Data
import pandas as pd
import numpy as np
def load_methylation_data(file_path, **kwargs):
"""Load methylation beta-value or M-value matrix.
Expected format:
- Rows: CpG probes (cg00000029, cg00000108, ...)
- Columns: Samples (TCGA-XX-XXXX, ...)
- Values: Beta values (0-1) or M-values (log2 ratio)
"""
ext = os.path.splitext(file_path)[1].lower()
if ext in ['.csv']:
df = pd.read_csv(file_path, index_col=0, **kwargs)
elif ext in ['.tsv', '.txt']:
df = pd.read_csv(file_path, sep='\t', index_col=0, **kwargs)
elif ext in ['.parquet']:
df = pd.read_parquet(file_path, **kwargs)
elif ext in ['.h5', '.hdf5']:
df = pd.read_hdf(file_path, **kwargs)
else:
# Try tab first, then comma
try:
df = pd.read_csv(file_path, sep='\t', index_col=0, **kwargs)
except Exception:
df = pd.read_csv(file_path, index_col=0, **kwargs)
return df
def detect_methylation_type(df):
"""Detect if data is beta values (0-1) or M-values (unbounded)."""
sample_vals = df.iloc[:1000, :5].values.flatten()
sample_vals = sample_vals[~np.isnan(sample_vals)]
if sample_vals.min() >= 0 and sample_vals.max() <= 1:
return 'beta'
else:
return 'mvalue'
def beta_to_mvalue(beta):
"""Convert beta values to M-values: M = log2(beta / (1 - beta))."""
beta = np.clip(beta, 1e-6, 1 - 1e-6)
return np.log2(beta / (1 - beta))
def mvalue_to_beta(mvalue):
"""Convert M-values to beta values: beta = 2^M / (2^M + 1)."""
return 2**mvalue / (2**mvalue + 1)
1.2 Load Methylation Manifest / Probe Annotation
def load_probe_annotation(manifest_path):
"""Load Illumina methylation array manifest.
Common columns: IlmnID, Name, CHR, MAPINFO (position), Strand,
UCSC_RefGene_Name, UCSC_RefGene_Group, Relation_to_UCSC_CpG_Island
"""
# Try reading manifest - may have header rows to skip
for skiprows in [0, 7, 8]:
try:
manifest = pd.read_csv(manifest_path, skiprows=skiprows,
low_memory=False)
if 'CHR' in manifest.columns or 'chr' in manifest.columns:
break
if 'Name' in manifest.columns or 'IlmnID' in manifest.columns:
break
except Exception:
continue
# Normalize column names
col_map = {}
for col in manifest.columns:
lower = col.lower()
if lower in ['chr', 'chromosome']:
col_map[col] = 'chr'
elif lower in ['mapinfo', 'position', 'pos', 'start']:
col_map[col] = 'position'
elif lower in ['name', 'ilmnid', 'probe_id', 'cpg_id']:
col_map[col] = 'probe_id'
elif 'refgene_name' in lower or 'gene' in lower:
col_map[col] = 'gene_name'
elif 'refgene_group' in lower:
col_map[col] = 'gene_group'
elif 'cpg_island' in lower or 'relation' in lower:
col_map[col] = 'cpg_island_relation'
manifest = manifest.rename(columns=col_map)
return manifest
def normalize_chromosome(chrom):
"""Normalize chromosome name: '1' -> 'chr1', 'chrX' -> 'chrX', etc."""
if chrom is None or pd.isna(chrom):
return None
chrom = str(chrom).strip()
if not chrom.startswith('chr'):
chrom = 'chr' + chrom
return chrom
def get_chromosome_lengths(genome='hg38'):
"""Return chromosome lengths for common genome builds."""
# hg38 chromosome sizes (main chromosomes)
hg38 = {
'chr1': 248956422, 'chr2': 242193529, 'chr3': 198295559,
'chr4': 190214555, 'chr5': 181538259, 'chr6': 170805979,
'chr7': 159345973, 'chr8': 145138636, 'chr9': 138394717,
'chr10': 133797422, 'chr11': 135086622, 'chr12': 133275309,
'chr13': 114364328, 'chr14': 107043718, 'chr15': 101991189,
'chr16': 90338345, 'chr17': 83257441, 'chr18': 80373285,
'chr19': 58617616, 'chr20': 64444167, 'chr21': 46709983,
'chr22': 50818468, 'chrX': 156040895, 'chrY': 57227415,
}
hg19 = {
'chr1': 249250621, 'chr2': 243199373, 'chr3': 198022430,
'chr4': 191154276, 'chr5': 180915260, 'chr6': 171115067,
'chr7': 159138663, 'chr8': 146364022, 'chr9': 141213431,
'chr10': 135534747, 'chr11': 135006516, 'chr12': 133851895,
'chr13': 115169878, 'chr14': 107349540, 'chr15': 102531392,
'chr16': 90354753, 'chr17': 81195210, 'chr18': 78077248,
'chr19': 59128983, 'chr20': 63025520, 'chr21': 48129895,
'chr22': 51304566, 'chrX': 155270560, 'chrY': 59373566,
}
mm10 = {
'chr1': 195471971, 'chr2': 182113224, 'chr3': 160039680,
'chr4': 156508116, 'chr5': 151834684, 'chr6': 149736546,
'chr7': 145441459, 'chr8': 129401213, 'chr9': 124595110,
'chr10': 130694993, 'chr11': 122082543, 'chr12': 120129022,
'chr13': 120421639, 'chr14': 124902244, 'chr15': 104043685,
'chr16': 98207768, 'chr17': 94987271, 'chr18': 90702639,
'chr19': 61431566, 'chrX': 171031299, 'chrY': 91744698,
}
genomes = {'hg38': hg38, 'hg19': hg19, 'mm10': mm10}
return genomes.get(genome, hg38)
1.3 CpG Site Filtering
def filter_cpg_probes(df, manifest=None, filters=None):
"""Filter CpG probes based on various criteria.
Args:
df: Methylation matrix (probes x samples)
manifest: Probe annotation DataFrame
filters: dict with keys:
- 'variance_threshold': float, minimum variance across samples
- 'mean_beta_range': tuple (min, max), filter probes with extreme mean beta
- 'missing_threshold': float (0-1), max fraction of NaN allowed per probe
- 'chromosomes': list, keep only these chromosomes
- 'exclude_sex_chr': bool, remove chrX and chrY
- 'probe_type': 'cg' or 'ch', keep only one type
- 'cpg_island': str ('Island', 'Shore', 'Shelf', 'OpenSea')
- 'gene_group': str ('TSS200', 'TSS1500', 'Body', '1stExon', etc.)
- 'top_n_variable': int, keep top N most variable probes
"""
if filters is None:
filters = {}
probe_mask = pd.Series(True, index=df.index)
# Probe type filter (cg vs ch)
if 'probe_type' in filters:
ptype = filters['probe_type']
probe_mask &= df.index.str.startswith(ptype)
# Missing data filter
if 'missing_threshold' in filters:
threshold = filters['missing_threshold']
missing_frac = df.isna().mean(axis=1)
probe_mask &= missing_frac <= threshold
# Variance filter
if 'variance_threshold' in filters:
var_threshold = filters['variance_threshold']
probe_var = df.var(axis=1, skipna=True)
probe_mask &= probe_var >= var_threshold
# Mean beta range filter
if 'mean_beta_range' in filters:
min_beta, max_beta = filters['mean_beta_range']
probe_mean = df.mean(axis=1, skipna=True)
probe_mask &= (probe_mean >= min_beta) & (probe_mean <= max_beta)
# Top N most variable
if 'top_n_variable' in filters:
n = filters['top_n_variable']
probe_var = df.var(axis=1, skipna=True)
top_probes = probe_var.nlargest(n).index
probe_mask &= df.index.isin(top_probes)
# Manifest-based filters
if manifest is not None and len(manifest) > 0:
probe_id_col = 'probe_id' if 'probe_id' in manifest.columns else manifest.columns[0]
manifest_indexed = manifest.set_index(probe_id_col) if probe_id_col in manifest.columns else manifest
# Chromosome filter
if 'chromosomes' in filters and 'chr' in manifest_indexed.columns:
valid_chr = [normalize_chromosome(c) for c in filters['chromosomes']]
chr_probes = manifest_indexed[
manifest_indexed['chr'].apply(normalize_chromosome).isin(valid_chr)
].index
probe_mask &= df.index.isin(chr_probes)
# Exclude sex chromosomes
if filters.get('exclude_sex_chr', False) and 'chr' in manifest_indexed.columns:
sex_chr = ['chrX', 'chrY', 'X', 'Y']
nonsex_probes = manifest_indexed[
~manifest_indexed['chr'].apply(normalize_chromosome).isin(['chrX', 'chrY'])
].index
probe_mask &= df.index.isin(nonsex_probes)
# CpG island relation filter
if 'cpg_island' in filters and 'cpg_island_relation' in manifest_indexed.columns:
relation = filters['cpg_island']
island_probes = manifest_indexed[
manifest_indexed['cpg_island_relation'].str.contains(relation, na=False, case=False)
].index
probe_mask &= df.index.isin(island_probes)
# Gene group filter (TSS200, Body, etc.)
if 'gene_group' in filters and 'gene_group' in manifest_indexed.columns:
group = filters['gene_group']
group_probes = manifest_indexed[
manifest_indexed['gene_group'].str.contains(group, na=False, case=False)
].index
probe_mask &= df.index.isin(group_probes)
filtered_df = df[probe_mask]
return filtered_df
1.4 Differential Methylation Analysis
from scipy import stats
import statsmodels.stats.multitest as mt
def differential_methylation(beta_df, group1_samples, group2_samples,
test='ttest', correction='fdr_bh', alpha=0.05):
"""Perform differential methylation analysis between two groups.
Args:
beta_df: Beta-value matrix (probes x samples)
group1_samples: list of sample IDs for group 1
group2_samples: list of sample IDs for group 2
test: 'ttest', 'wilcoxon', or 'ks' (Kolmogorov-Smirnov)
correction: multiple testing correction method
alpha: significance threshold
Returns:
DataFrame with columns: mean_g1, mean_g2, delta_beta, pvalue, padj
"""
g1 = beta_df[group1_samples]
g2 = beta_df[group2_samples]
results = []
for probe in beta_df.index:
vals1 = g1.loc[probe].dropna().values
vals2 = g2.loc[probe].dropna().values
if len(vals1) < 2 or len(vals2) < 2:
results.append({
'probe': probe, 'mean_g1': np.nan, 'mean_g2': np.nan,
'delta_beta': np.nan, 'pvalue': np.nan
})
continue
mean1 = np.nanmean(vals1)
mean2 = np.nanmean(vals2)
delta = mean2 - mean1
if test == 'ttest':
stat, pval = stats.ttest_ind(vals1, vals2, equal_var=False)
elif test == 'wilcoxon':
stat, pval = stats.mannwhitneyu(vals1, vals2, alternative='two-sided')
elif test == 'ks':
stat, pval = stats.ks_2samp(vals1, vals2)
else:
stat, pval = stats.ttest_ind(vals1, vals2, equal_var=False)
results.append({
'probe': probe, 'mean_g1': mean1, 'mean_g2': mean2,
'delta_beta': delta, 'pvalue': pval
})
result_df = pd.DataFrame(results).set_index('probe')
# Multiple testing correction
valid_pvals = result_df['pvalue'].dropna()
if len(valid_pvals) > 0:
reject, padj, _, _ = mt.multipletests(valid_pvals.values, alpha=alpha, method=correction)
result_df.loc[valid_pvals.index, 'padj'] = padj
else:
result_df['padj'] = np.nan
return result_df
def identify_dmps(dm_results, alpha=0.05, delta_beta_threshold=0.0):
"""Identify differentially methylated positions (DMPs).
Args:
dm_results: Output from differential_methylation()
alpha: adjusted p-value threshold
delta_beta_threshold: minimum absolute beta-value difference
Returns:
DataFrame of significant DMPs
"""
dmps = dm_results[
(dm_results['padj'] < alpha) &
(dm_results['delta_beta'].abs() >= delta_beta_threshold)
].copy()
dmps['direction'] = np.where(dmps['delta_beta'] > 0, 'hyper', 'hypo')
return dmps.sort_values('padj')
1.5 Age-Related CpG Analysis
def identify_age_related_cpgs(beta_df, ages, method='correlation',
correction='fdr_bh', alpha=0.05):
"""Identify CpG sites associated with age.
Args:
beta_df: Beta-value matrix (probes x samples)
ages: Series or array of ages corresponding to samples
method: 'correlation' (Pearson/Spearman) or 'regression'
correction: multiple testing method
alpha: significance threshold
Returns:
DataFrame with correlation, p-value, adjusted p-value
"""
results = []
for probe in beta_df.index:
vals = beta_df.loc[probe].values
mask = ~np.isnan(vals) & ~np.isnan(ages.values if hasattr(ages, 'values') else ages)
if sum(mask) < 5:
results.append({'probe': probe, 'correlation': np.nan,
'pvalue': np.nan})
continue
if method == 'correlation':
corr, pval = stats.pearsonr(ages[mask] if hasattr(ages, '__getitem__') else
np.array(ages)[mask], vals[mask])
elif method == 'spearman':
corr, pval = stats.spearmanr(ages[mask] if hasattr(ages, '__getitem__') else
np.array(ages)[mask], vals[mask])
else:
corr, pval = stats.pearsonr(ages[mask] if hasattr(ages, '__getitem__') else
np.array(ages)[mask], vals[mask])
results.append({'probe': probe, 'correlation': corr, 'pvalue': pval})
result_df = pd.DataFrame(results).set_index('probe')
# Multiple testing correction
valid_pvals = result_df['pvalue'].dropna()
if len(valid_pvals) > 0:
reject, padj, _, _ = mt.multipletests(valid_pvals.values, alpha=alpha, method=correction)
result_df.loc[valid_pvals.index, 'padj'] = padj
else:
result_df['padj'] = np.nan
return result_df
1.6 Chromosome-Level Methylation Statistics
def chromosome_cpg_density(cpg_probes, manifest, genome='hg38'):
"""Calculate CpG density per chromosome.
Args:
cpg_probes: list/Index of CpG probe IDs
manifest: probe annotation with chr and position columns
genome: genome build for chromosome lengths
Returns:
DataFrame with chr, n_cpgs, chr_length, density (CpGs per bp)
"""
chr_lengths = get_chromosome_lengths(genome)
# Map probes to chromosomes
probe_id_col = 'probe_id' if 'probe_id' in manifest.columns else manifest.columns[0]
if probe_id_col in manifest.columns:
probe_chr = manifest.set_index(probe_id_col)
else:
probe_chr = manifest
# Get chromosome for each probe
if 'chr' in probe_chr.columns:
chr_col = 'chr'
elif 'CHR' in probe_chr.columns:
chr_col = 'CHR'
else:
raise ValueError("No chromosome column found in manifest")
# Count probes per chromosome
probe_chrs = probe_chr.loc[probe_chr.index.isin(cpg_probes), chr_col]
probe_chrs = probe_chrs.apply(normalize_chromosome)
chr_counts = probe_chrs.value_counts()
results = []
for chrom, count in chr_counts.items():
if chrom in chr_lengths:
length = chr_lengths[chrom]
density = count / length
results.append({
'chr': chrom,
'n_cpgs': count,
'chr_length': length,
'density_per_bp': density,
'density_per_mb': density * 1e6,
})
return pd.DataFrame(results).sort_values('chr',
key=lambda x: x.str.replace('chr', '').replace({'X': '23', 'Y': '24'}).astype(int))
def genome_wide_average_density(density_df):
"""Calculate genome-wide average CpG density across all chromosomes.
Args:
density_df: Output from chromosome_cpg_density()
Returns:
float: genome-wide average density (CpGs per bp)
"""
total_cpgs = density_df['n_cpgs'].sum()
total_length = density_df['chr_length'].sum()
return total_cpgs / total_length
def chromosome_density_ratio(density_df, chr1, chr2):
"""Calculate density ratio between two chromosomes.
Args:
density_df: Output from chromosome_cpg_density()
chr1, chr2: chromosome names (e.g., 'chr1', 'chr2')
Returns:
float: density ratio (chr1 / chr2)
"""
chr1 = normalize_chromosome(chr1)
chr2 = normalize_chromosome(chr2)
d1 = density_df[density_df['chr'] == chr1]['density_per_bp'].values[0]
d2 = density_df[density_df['chr'] == chr2]['density_per_bp'].values[0]
return d1 / d2
Phase 2: ChIP-seq Peak Analysis
2.1 Load BED/Peak Files
def load_bed_file(file_path, format='bed'):
"""Load BED format file (standard BED, narrowPeak, broadPeak).
Standard BED: chrom, start, end, name, score, strand
narrowPeak: + signalValue, pValue, qValue, peak
broadPeak: + signalValue, pValue, qValue
"""
if format == 'narrowPeak' or file_path.endswith('.narrowPeak'):
names = ['chrom', 'start', 'end', 'name', 'score', 'strand',
'signalValue', 'pValue', 'qValue', 'peak']
elif format == 'broadPeak' or file_path.endswith('.broadPeak'):
names = ['chrom', 'start', 'end', 'name', 'score', 'strand',
'signalValue', 'pValue', 'qValue']
else:
# Standard BED - detect number of columns
with open(file_path, 'r') as f:
first_line = f.readline().strip()
while first_line.startswith('#') or first_line.startswith('track') or first_line.startswith('browser'):
first_line = f.readline().strip()
n_cols = len(first_line.split('\t'))
bed_col_names = ['chrom', 'start', 'end', 'name', 'score', 'strand',
'thickStart', 'thickEnd', 'itemRgb', 'blockCount',
'blockSizes', 'blockStarts']
names = bed_col_names[:n_cols]
df = pd.read_csv(file_path, sep='\t', header=None, names=names,
comment='#', low_memory=False)
# Skip track/browser lines
df = df[~df['chrom'].astype(str).str.startswith(('track', 'browser'))]
# Normalize chromosomes
df['chrom'] = df['chrom'].apply(normalize_chromosome)
# Ensure numeric types
df['start'] = pd.to_numeric(df['start'], errors='coerce')
df['end'] = pd.to_numeric(df['end'], errors='coerce')
return df
def peak_statistics(peaks_df):
"""Calculate basic peak statistics.
Args:
peaks_df: BED DataFrame from load_bed_file()
Returns:
dict with peak statistics
"""
peaks_df = peaks_df.copy()
peaks_df['length'] = peaks_df['end'] - peaks_df['start']
stats_dict = {
'total_peaks': len(peaks_df),
'mean_peak_length': peaks_df['length'].mean(),
'median_peak_length': peaks_df['length'].median(),
'total_coverage_bp': peaks_df['length'].sum(),
'peaks_per_chromosome': peaks_df['chrom'].value_counts().to_dict(),
}
if 'signalValue' in peaks_df.columns:
stats_dict['mean_signal'] = peaks_df['signalValue'].mean()
stats_dict['median_signal'] = peaks_df['signalValue'].median()
if 'qValue' in peaks_df.columns:
stats_dict['mean_qvalue'] = peaks_df['qValue'].mean()
return stats_dict
2.2 Peak Annotation
def annotate_peaks_to_genes(peaks_df, gene_annotation=None,
tss_upstream=2000, tss_downstream=500):
"""Annotate peaks to nearest gene / genomic feature.
Args:
peaks_df: BED DataFrame
gene_annotation: DataFrame with gene coordinates (chr, start, end, gene_name, strand)
tss_upstream: bp upstream of TSS to define promoter
tss_downstream: bp downstream of TSS to define promoter
Returns:
DataFrame with peak annotations
"""
if gene_annotation is None:
return peaks_df # No annotation available
annotated = peaks_df.copy()
annotations = []
for _, peak in peaks_df.iterrows():
peak_chr = peak['chrom']
peak_mid = (peak['start'] + peak['end']) // 2
# Filter genes on same chromosome
chr_genes = gene_annotation[gene_annotation['chr'] == peak_chr]
if len(chr_genes) == 0:
annotations.append({
'nearest_gene': 'intergenic',
'distance_to_tss': np.nan,
'feature': 'intergenic'
})
continue
# Calculate distance to TSS
tss_positions = chr_genes.apply(
lambda g: g['start'] if g.get('strand', '+') == '+' else g['end'],
axis=1
)
distances = (peak_mid - tss_positions).abs()
nearest_idx = distances.idxmin()
nearest_gene = chr_genes.loc[nearest_idx]
distance = distances.loc[nearest_idx]
tss = tss_positions.loc[nearest_idx]
# Classify feature type
if abs(peak_mid - tss) <= tss_upstream:
feature = 'promoter'
elif peak['start'] >= nearest_gene['start'] and peak['end'] <= nearest_gene['end']:
feature = 'gene_body'
elif abs(peak_mid - tss) <= 10000:
feature = 'proximal'
else:
feature = 'distal'
annotations.append({
'nearest_gene': nearest_gene.get('gene_name', nearest_gene.name),
'distance_to_tss': int(distance),
'feature': feature
})
ann_df = pd.DataFrame(annotations, index=peaks_df.index)
return pd.concat([peaks_df, ann_df], axis=1)
def classify_peak_regions(annotated_peaks):
"""Classify peaks into genomic regions.
Returns:
dict with counts per region type
"""
if 'feature' not in annotated_peaks.columns:
return {'unknown': len(annotated_peaks)}
return annotated_peaks['feature'].value_counts().to_dict()
2.3 Peak Overlap Analysis
def find_overlaps(peaks_a, peaks_b, min_overlap=1):
"""Find overlapping peaks between two BED DataFrames.
Uses a simple interval overlap approach (pure Python, no pybedtools).
Args:
peaks_a: BED DataFrame (query)
peaks_b: BED DataFrame (subject)
min_overlap: minimum overlap in bp
Returns:
DataFrame of overlapping pairs
"""
overlaps = []
# Group by chromosome for efficiency
for chrom in peaks_a['chrom'].unique():
a_chr = peaks_a[peaks_a['chrom'] == chrom].sort_values('start')
b_chr = peaks_b[peaks_b['chrom'] == chrom].sort_values('start')
if len(b_chr) == 0:
continue
for _, a_peak in a_chr.iterrows():
# Binary search for potential overlaps
for _, b_peak in b_chr.iterrows():
if b_peak['start'] >= a_peak['end']:
break
if b_peak['end'] <= a_peak['start']:
continue
# Calculate overlap
overlap_start = max(a_peak['start'], b_peak['start'])
overlap_end = min(a_peak['end'], b_peak['end'])
overlap_bp = overlap_end - overlap_start
if overlap_bp >= min_overlap:
overlaps.append({
'a_chrom': chrom,
'a_start': a_peak['start'],
'a_end': a_peak['end'],
'b_start': b_peak['start'],
'b_end': b_peak['end'],
'overlap_bp': overlap_bp,
})
return pd.DataFrame(overlaps) if overlaps else pd.DataFrame()
def jaccard_similarity(peaks_a, peaks_b, genome='hg38'):
"""Calculate Jaccard similarity between two peak sets.
Jaccard = intersection / union of genomic coverage.
"""
chr_lengths = get_chromosome_lengths(genome)
total_genome = sum(chr_lengths.values())
# Simple approximation: total bp covered
coverage_a = (peaks_a['end'] - peaks_a['start']).sum()
coverage_b = (peaks_b['end'] - peaks_b['start']).sum()
overlaps = find_overlaps(peaks_a, peaks_b)
if len(overlaps) == 0:
return 0.0
intersection = overlaps['overlap_bp'].sum()
union = coverage_a + coverage_b - intersection
return intersection / union if union > 0 else 0.0
Phase 3: ATAC-seq Analysis
3.1 ATAC-seq Peak Processing
def load_atac_peaks(file_path):
"""Load ATAC-seq peak file (typically narrowPeak format)."""
return load_bed_file(file_path, format='narrowPeak')
def atac_peak_statistics(peaks_df):
"""ATAC-seq specific statistics.
ATAC-seq peaks represent open chromatin regions.
"""
basic_stats = peak_statistics(peaks_df)
# ATAC-specific: nucleosome-free region (NFR) analysis
# NFR peaks typically < 150bp
peaks_df = peaks_df.copy()
peaks_df['length'] = peaks_df['end'] - peaks_df['start']
nfr_peaks = peaks_df[peaks_df['length'] < 150]
nucleosome_peaks = peaks_df[peaks_df['length'] >= 150]
basic_stats['nfr_peaks'] = len(nfr_peaks)
basic_stats['nucleosome_peaks'] = len(nucleosome_peaks)
basic_stats['nfr_fraction'] = len(nfr_peaks) / len(peaks_df) if len(peaks_df) > 0 else 0
return basic_stats
def chromatin_accessibility_by_region(peaks_df, gene_annotation=None):
"""Calculate chromatin accessibility distribution across genomic regions."""
annotated = annotate_peaks_to_genes(peaks_df, gene_annotation)
regions = classify_peak_regions(annotated)
total = sum(regions.values())
region_fractions = {k: v / total for k, v in regions.items()}
return {
'counts': regions,
'fractions': region_fractions,
'total_peaks': total,
}
Phase 4: Multi-Omics Integration
4.1 Expression-Methylation Correlation
def correlate_methylation_expression(beta_df, expression_df, probe_gene_map,
method='pearson', correction='fdr_bh'):
"""Correlate methylation levels with gene expression.
Args:
beta_df: Methylation matrix (probes x samples)
expression_df: Expression matrix (genes x samples)
probe_gene_map: dict or Series mapping probe IDs to gene symbols
method: 'pearson' or 'spearman'
correction: multiple testing correction
Returns:
DataFrame with correlation, p-value per probe-gene pair
"""
# Align samples
common_samples = list(set(beta_df.columns) & set(expression_df.columns))
if len(common_samples) < 5:
raise ValueError(f"Not enough common samples: {len(common_samples)}")
beta_aligned = beta_df[common_samples]
expr_aligned = expression_df[common_samples]
results = []
for probe, gene in probe_gene_map.items():
if probe not in beta_aligned.index or gene not in expr_aligned.index:
continue
meth_vals = beta_aligned.loc[probe].values
expr_vals = expr_aligned.loc[gene].values
mask = ~np.isnan(meth_vals) & ~np.isnan(expr_vals)
if sum(mask) < 5:
continue
if method == 'pearson':
corr, pval = stats.pearsonr(meth_vals[mask], expr_vals[mask])
else:
corr, pval = stats.spearmanr(meth_vals[mask], expr_vals[mask])
results.append({
'probe': probe,
'gene': gene,
'correlation': corr,
'pvalue': pval,
'n_samples': sum(mask),
})
result_df = pd.DataFrame(results)
if len(result_df) > 0:
valid_pvals = result_df['pvalue'].dropna()
if len(valid_pvals) > 0:
reject, padj, _, _ = mt.multipletests(valid_pvals.values, method=correction)
result_df.loc[valid_pvals.index, 'padj'] = padj
return result_df
4.2 ChIP-seq + Expression Integration
def integrate_chipseq_expression(peaks_df, expression_df, gene_annotation,
tss_window=5000):
"""Integrate ChIP-seq peaks with gene expression.
Args:
peaks_df: ChIP-seq peaks (BED)
expression_df: Gene expression (genes x samples)
gene_annotation: Gene coordinates
tss_window: window around TSS for promoter peaks
Returns:
DataFrame with genes having promoter peaks and their expression
"""
annotated = annotate_peaks_to_genes(peaks_df, gene_annotation,
tss_upstream=tss_window)
promoter_peaks = annotated[annotated['feature'] == 'promoter']
# Get genes with promoter peaks
peak_genes = promoter_peaks['nearest_gene'].unique()
# Get expression for these genes
common_genes = [g for g in peak_genes if g in expression_df.index]
result = pd.DataFrame({
'gene': common_genes,
'has_promoter_peak': True,
'mean_expression': [expression_df.loc[g].mean() for g in common_genes],
})
return result
Phase 5: Clinical Data Integration
5.1 Missing Data Analysis
def missing_data_analysis(clinical_df=None, expression_df=None,
methylation_df=None, sample_id_col=None):
"""Analyze missing data across multiple omics modalities.
For BixBench questions like:
"How many patients have no missing data for vital status, gene expression, and methylation?"
Args:
clinical_df: Clinical data (patients x variables)
expression_df: Expression matrix (genes x samples)
methylation_df: Methylation matrix (probes x samples)
sample_id_col: Column name for sample/patient IDs in clinical data
Returns:
dict with completeness statistics
"""
results = {}
# Get sample sets from each modality
clinical_samples = set()
if clinical_df is not None:
if sample_id_col and sample_id_col in clinical_df.columns:
clinical_samples = set(clinical_df[sample_id_col].dropna())
else:
clinical_samples = set(clinical_df.index)
results['clinical_samples'] = len(clinical_samples)
expression_samples = set()
if expression_df is not None:
expression_samples = set(expression_df.columns)
results['expression_samples'] = len(expression_samples)
methylation_samples = set()
if methylation_df is not None:
methylation_samples = set(methylation_df.columns)
results['methylation_samples'] = len(methylation_samples)
# Intersection: samples with ALL data types
all_sets = []
if clinical_samples:
all_sets.append(clinical_samples)
if expression_samples:
all_sets.append(expression_samples)
if methylation_samples:
all_sets.append(methylation_samples)
if len(all_sets) > 0:
complete_samples = set.intersection(*all_sets)
results['complete_samples'] = len(complete_samples)
results['complete_sample_ids'] = sorted(complete_samples)
else:
results['complete_samples'] = 0
# Additional: check for missing values within clinical data
if clinical_df is not None:
for col in clinical_df.columns:
n_missing = clinical_df[col].isna().sum()
n_total = len(clinical_df)
results[f'clinical_{col}_missing'] = n_missing
results[f'clinical_{col}_complete'] = n_total - n_missing
return results
def find_complete_cases(data_frames, variables=None):
"""Find samples that are complete across specified data frames and variables.
Args:
data_frames: dict of {name: DataFrame} where columns are samples
variables: dict of {df_name: [variable_names]} for clinical variables to check
Returns:
set of sample IDs with complete data
"""
sample_sets = []
for name, df in data_frames.items():
if df is not None:
if variables and name in variables:
# Check specific variables for completeness
for var in variables[name]:
if var in df.columns:
complete = set(df[df[var].notna()].index)
sample_sets.append(complete)
elif var in df.index:
complete = set(df.columns[df.loc[var].notna()])
sample_sets.append(complete)
else:
# Just check sample presence
sample_sets.append(set(df.columns))
if not sample_sets:
return set()
return set.intersection(*sample_sets)
Phase 6: ToolUniverse Annotation Integration
Use ToolUniverse tools for biological annotation of epigenomic findings.
6.1 Gene-Level Annotation
from tooluniverse import ToolUniverse
tu = ToolUniverse()
tu.load_tools()
# Annotate differentially methylated genes
def annotate_genes_with_tooluniverse(gene_list, tu):
"""Annotate a list of genes using ToolUniverse tools.
Uses:
- Ensembl for gene coordinates and cross-references
- SCREEN for regulatory elements near gene
- ChIPAtlas for ChIP-seq experiments
"""
annotations = {}
for gene in gene_list[:20]: # Limit for API rate
annotation = {'gene': gene}
# Ensembl lookup
try:
ens = tu.tools.ensembl_lookup_gene(id=gene, species='homo_sapiens')
if isinstance(ens, dict):
data = ens.get('data', ens)
annotation['ensembl_id'] = data.get('id', 'N/A')
annotation['chr'] = data.get('seq_region_name', 'N/A')
annotation['start'] = data.get('start', 'N/A')
annotation['end'] = data.get('end', 'N/A')
annotation['biotype'] = data.get('biotype', 'N/A')
except Exception:
pass
# SCREEN regulatory elements
try:
screen = tu.tools.SCREEN_get_regulatory_elements(
gene_name=gene, element_type="enhancer", limit=5
)
if screen is not None:
annotation['screen_enhancers'] = 'available'
except Exception:
pass
annotations[gene] = annotation
return pd.DataFrame.from_dict(annotations, orient='index')
6.2 ChIPAtlas Integration
def query_chipatlas_experiments(antigen, genome='hg38', cell_type=None, tu=None):
"""Query ChIPAtlas for available ChIP-seq experiments.
Args:
antigen: TF or histone mark name (e.g., 'H3K27ac', 'CTCF')
genome: genome build
cell_type: optional cell type filter
Returns:
ChIPAtlas experiment metadata
"""
if tu is None:
from tooluniverse import ToolUniverse
tu = ToolUniverse()
tu.load_tools()
params = {
'operation': 'get_experiment_list',
'genome': genome,
'antigen': antigen,
'limit': 50,
}
if cell_type:
params['cell_type'] = cell_type
return tu.tools.ChIPAtlas_get_experiments(**params)
6.3 Ensembl Regulatory Feature Annotation
def annotate_regions_with_ensembl(regions, species='human', tu=None):
"""Annotate genomic regions with Ensembl regulatory features.
Args:
regions: list of (chr, start, end) tuples
species: Ensembl species name
Returns:
dict of region -> regulatory features
"""
if tu is None:
from tooluniverse import ToolUniverse
tu = ToolUniverse()
tu.load_tools()
annotations = {}
for chrom, start, end in regions[:10]: # Limit for API rate
# Ensembl uses chromosome without 'chr' prefix
ens_chrom = chrom.replace('chr', '') if chrom.startswith('chr') else chrom
region_str = f"{ens_chrom}:{start}-{end}"
try:
result = tu.tools.ensembl_get_regulatory_features(
region=region_str, feature="regulatory", species=species
)
annotations[(chrom, start, end)] = result
except Exception as e:
annotations[(chrom, start, end)] = {'error': str(e)}
return annotations
Clinical data: Patient/sample-centric with clinical variables as columns
Fallback Strategies
Scenario
Primary
Fallback
No manifest file
Load from data dir
Build minimal from Ensembl lookup
No pybedtools
Pure Python overlap
pandas-based interval intersection
No pyBigWig
Skip BigWig analysis
Use pre-computed summary tables
Missing clinical data
Report missing
Use available samples only
Low sample count
Parametric test
Use non-parametric (Wilcoxon)
Large dataset (>500K probes)
Full analysis
Sample or chunk-based processing
Common Use Patterns
Pattern 1: Methylation Array Analysis
Input: Beta-value matrix + manifest + clinical data
Question: "How many CpGs are differentially methylated?"
Flow:
1. Load beta matrix, manifest, clinical data
2. Filter CpG probes (cg only, remove sex chr, variance filter)
3. Define groups from clinical data
4. Run differential_methylation()
5. Apply thresholds (padj < 0.05, |delta_beta| > 0.2)
6. Report count and direction (hyper/hypo)
Pattern 2: Age-Related CpG Density
Input: Beta-value matrix + manifest + ages
Question: "What is the density ratio of age-related CpGs between chr1 and chr2?"
Flow:
1. Load beta matrix and ages from clinical data
2. Run identify_age_related_cpgs()
3. Filter significant age-related CpGs
4. Map to chromosomes using manifest
5. Calculate chromosome_cpg_density()
6. Compute ratio between specified chromosomes
Pattern 3: Multi-Omics Missing Data
Input: Clinical + expression + methylation data files
Question: "How many patients have complete data for all modalities?"
Flow:
1. Load all data files
2. Extract sample IDs from each
3. Find intersection (common samples)
4. Check for NaN/missing within clinical variables
5. Report complete cases count
Pattern 4: ChIP-seq Peak Annotation
Input: BED/narrowPeak file
Question: "What fraction of peaks are in promoter regions?"
Flow:
1. Load BED file with load_bed_file()
2. Load or fetch gene annotation (Ensembl)
3. Run annotate_peaks_to_genes()
4. Classify regions with classify_peak_regions()
5. Calculate fraction in promoters
Pattern 5: Methylation-Expression Integration
Input: Beta matrix + expression matrix + probe-gene mapping
Question: "What is the correlation between methylation and expression?"
Flow:
1. Load both matrices
2. Build probe-gene map from manifest
3. Align samples across datasets
4. Run correlate_methylation_expression()
5. Report significant anti-correlations
Edge Cases
Missing Probe Annotation
When no manifest/annotation file is available:
Extract chromosome from probe ID naming patterns if possible
Use ToolUniverse Ensembl tools to build minimal annotation
Report limitation: "chromosome mapping unavailable for X probes"
Mixed Genome Builds
When data uses different builds:
Detect build from context (data README, file names, known coordinates)
Use appropriate chromosome lengths for density calculations
Do NOT mix hg19 and hg38 coordinates
Very Large Datasets
For datasets with >500K CpG sites:
Use chunked processing for differential methylation
Pre-filter by variance before statistical testing
Use vectorized operations (avoid row-by-row loops where possible)
Sample ID Mismatches
Clinical and molecular data may use different ID formats:
TCGA: barcode (TCGA-XX-XXXX-01A) vs patient ID (TCGA-XX-XXXX)
Try truncating or matching partial IDs
Report number of matched/unmatched samples
Limitations
No native pybedtools: Uses pure Python interval operations (slower for very large BED files)
No native pyBigWig: Cannot read BigWig files directly without package
No R bridge: Does not use methylKit, ChIPseeker, or DiffBind
Illumina-centric: Methylation functions designed for 450K/EPIC arrays
Statistical simplicity: Uses t-test/Wilcoxon for differential methylation (not limma/bumphunter)
No peak calling: Assumes peaks are pre-called; does not run MACS2 or similar
API rate limits: ToolUniverse annotation limited to ~20 genes per batch
Summary
Genomics & Epigenomics Data Processing Skill provides: