Annotating limma Results with Gene Names for Affy Microarrays

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Lately I’ve been using the limma package often for analyzing microarray data. When I read in Affy CEL files using ReadAffy(), the resulting ExpressionSet won’t contain any featureData annotation. Consequentially, when I run topTable to get a list of differentially expressed genes, there’s no annotation information other than the Affymetrix probeset IDs or transcript cluster IDs. There are other ways of annotating these results (INNER JOIN to a MySQL database, biomaRt, etc), but I would like to have the output from topTable already annotated with gene information. Ideally, I could annotate each probeset ID with a gene symbol, gene name, Ensembl ID, and have that Ensembl ID hyperlink out to the Ensembl genome browser. With some help from Gordon Smyth on the Bioconductor Mailing list, I found that annotating the ExpressionSet object results in the output from topTable also being annotated.

The results from topTable are pretty uninformative without annotation:

After annotation:

You can generate an HTML file with clickable links to the Ensembl Genome Browser for each gene:

Here’s the R code to do it:

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