In perishky/meffil: Efficient algorithms for DNA methylation

library(knitr)
library(Cairo)
opts_chunk$set(warning=FALSE, fig.width=6, fig.height=6, dev="CairoPNG", stop=TRUE)

Normalize an 450K, EPIC and EPIC v2 dataset

Download example data set

path.450k <- download.450k.demo.dataset()
path.epic <- download.epic.demo.dataset()
path.epic2 <- download.epic2.demo.dataset()

Normalize dataset

Create samplesheet

library(meffil)
samplesheet.450k <- meffil.create.samplesheet(path=path.450k)
samplesheet.epic <- meffil.read.samplesheet(base=path.epic, pattern="Demo_SampleSheet.csv")
samplesheet.epic2 <- meffil.read.samplesheet(base=path.epic2, pattern="SampleSheet")
samplesheet.450k$chip <- "450k"
samplesheet.epic$chip <- "epic"
samplesheet.epic2$chip <- "epic2"
common.cols <- intersect(colnames(samplesheet.450k),colnames(samplesheet.epic))
common.cols <- intersect(common.cols, colnames(samplesheet.epic2))
samplesheet <- rbind(
    samplesheet.450k[1:10,common.cols],
    samplesheet.epic[,common.cols],
    samplesheet.epic2[,common.cols])

Parameters.

qc.file <- "complex-demo/qc-report.html"
author <- "Illumina, et al."
study <- "450k/epic/epic2 demo dataset"
number.pcs <- 2
norm.file <- "complex-demo/normalization-report.html"

Generate QC objects.

options(mc.core=20)
qc.objects <- meffil.qc(samplesheet, featureset="450k:epic:epic2", cell.type.reference="blood gse35069 complete", verbose=T)

QC report.

qc.summary <- meffil.qc.summary(qc.objects, verbose=T)
meffil.qc.report(
    qc.summary,
    output.file=qc.file,
    author=author,
    study=study)

Normalization dataset.

norm.objects <- meffil.normalize.quantiles(
    qc.objects,
    number.pcs=number.pcs,
    verbose=T)
beta.meffil <- meffil.normalize.samples(
    norm.objects,
    just.beta=T, 
    cpglist.remove=qc.summary$bad.cpgs$name,
    verbose=T)

Compute principal components of the normalized methylation matrix.

pcs <- meffil.methylation.pcs(
    beta.meffil,
    sites=meffil.get.autosomal.sites("epic"),
    verbose=T)

Normalization report.

parameters <- meffil.normalization.parameters(norm.objects)
parameters$batch.threshold <- 0.01
norm.summary <- meffil.normalization.summary(
    norm.objects=norm.objects,
    pcs=pcs,
    parameters=parameters,
    verbose=T)
meffil.normalization.report(
    norm.summary,
    output.file=norm.file,
    author=author,
    study=study)

It looks like the normalized methylation retains has a strong association with chip.

chip <- samplesheet$chip
stats <- t(apply(pcs,2,function(pc) {
    fit <- coef(summary(lm(pc ~ chip)))
    fit[which.min(fit[-1,"Pr(>|t|)"])+1,]
}))
stats[stats[,"Pr(>|t|)"] < 0.05,]

This isn't surprising given that the data for each chip comes from a different study. If there was reason to believe that the the chip associations were entirely technical, then we could remove some of this variation by including 'chip' as a random effect in the functional normalization.

perishky/meffil documentation built on Feb. 1, 2025, 6:53 p.m.