DNA microarray analysis identifies genes that are differentially expressed between Ig-mutated and Ig-unmutated CLL. The relative level of gene expression is depicted according to the color gradient at the bottom. For each array element, the scale is centered at the best distinction cutoff between the CLL subtypes. Red indicates higher expression, and green indicates lower expression of a given gene in the respective subgroup. (A) Expression profile of CLL subtype distinction genes. Relative expression levels of 304 Lymphochip array elements representing approximately 240 genes that were differentially expressed between Ig-mutated and Ig-unmutated CLL at a significance of P < .001 are shown. Columns represent individual patients (n = 107), and rows represent individual array elements. (B) ZAP-70 is the best CLL subtype distinction gene. The 30 most differentially expressed (P < .00001) genes between Ig-mutated and Ig-unmutated CLL are shown. Patients are grouped by their IgVH mutation status and, within subtypes, are arranged by the relative expression level of ZAP-70. Patients discordant for IgVH mutation status and ZAP-70 expression (ZAP-70 outliers) appear at the left (Ig-mutated CLL, ZAP-70 expression above cutoff) and right (Ig-unmutated CLL, ZAP-70 expression below cutoff) ends of the spectrum. Genes are labeled with the gene symbols. For unnamed genes the IMAGE clone numbers (IM) are given. The upper half contains genes more highly expressed in Ig-unmutated CLL and the lower half contains genes more highly expressed in Ig-mutated CLL. In each group, genes are arranged from top to bottom in descending order of statistical significance.