Recently, various deoxyribonucleic acid (DNA) microarray technologies to quantify the gene expression on a genome-wide scale have been developed to identify genes and pathways underlying complex disorders. DNA microarray approaches provide the ability to measure the expression levels of thousands of genes simultaneously. Common DNA microarray study objectives are (a) the identi cation of signi cant genes that are differentially expressed between two or more biological conditions, (b) the generation of possible hypotheses about the mechanisms underlying the observed phenotypes, and (c) the identi cation of gene expression patterns or “gene signatures” for classi cation purposes.