Annotating limma Results with Gene Names for Affy Microarrays

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: