Limma paired sample analysis
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@anandprem1792-13905
Last seen 7.0 years ago

I have an Affymetrix single channel DNA microarray dataset where normal and diseased tissue are taken from the same organ from 5 persons. So I have 10 CEL files with me. Now I want to analyse the differential gene expression between the normal and diseased tissues. I think I should use Limma Paired samples design matrix and compute paired moderated t test. Limma user guide. 9.4.1 pg no: 42 and 43. 

Can anyone please confirm whether my approach is correct or Should I follow different approach ?

My phenodata file looks like this 

FileName Subject Tissue
100.CEL 1 NORMAL
101.CEL 1 DISEASED
102.CEL 2 NORMAL
103.CEL 2 DISEASED
104.CEL 3 NORMAL
105.CEL 3 DISEASED
106.CEL 4 NORMAL
107.CEL 4 DISEASED
108.CEL 5 NORMAL
109.CEL 5 DISEASED

My code 

library(affy)

library(limma)

# Read all CEL FIles and put into an affybatch 
affy.data = ReadAffy()

#Importing the phenotype data
pData(affy.data) = read.table("phenodata.txt",  header=TRUE, row.names=1, as.is=TRUE)


#Visualise the phenotype data
pData(affy.data)

# Normalize the data
eset = rma(affy.data)

# DIFFERENTALLY GENE EXPRESSION ANALYSIS

library(limma)
pData(eset)
Subject <- factor(eset$Subject)

Tissue <- factor(eset$Tissue, levels = c("Normal", "Diseased"))

design <- model.matrix(~Subject+Tissue)
design

fit <- lmFit(eset, design)
eBayesfit <- eBayes(fit)

View(eBayesfit)
topTable(eBayesfit, coef="TissueDiseased")

limma design matrix limma paired analysis limma • 9.4k views
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Entering edit mode
Aaron Lun ★ 28k
@alun
Last seen 2 hours ago
The city by the bay

Looks fine to me. You should probably do some filtering on abundance, though. See the relevant section of the user's guide and case studies for examples. 

P.S. limma should be a separate tag, otherwise the maintainers don't get notified. 

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Thank you for the clarification. 

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