Probes and GO ontologies differently expressed between AML samples of young and old patients. (A) The transcriptome of AML samples of the 175 oldest patients was compared with the transcriptome of AML samples of the 175 youngest patients. This comparison revealed 477 probe sets that were higher expressed in the older age group (“Up-with-Age” group) and 492 that were lower expressed in the older age group (“Down-with-Age” group) at the significance level of P < .00001. An independent publicly available gene expression profiling cohort of 180 samples²⁶  was used to validate the differentially expressed probe sets between younger and older AML patients (validation step 1). Hereafter another publicly available cohort of 170 samples was used (validation step 2).²⁷  After 2 validation steps, 9 probe sets, representing 7 unique genes, were found to be higher expressed in older AML patients compared with younger AML patients; and 32 probe sets, representing 26 unique genes, were found to be lower expressed in older AML patients compared with younger AML patients. (B) Biologic processes (represented by GO ontologies) enriched among the 477 (up) and 492 (down) differentially expressed probe sets revealed 76 significantly “Up-with-Age” and 95 significantly “Down-with-Age” GO ontologies (P < .01). Next, GO ontologies enriched among the 145 significantly “Up-with-Age” and 257 significantly “Down-with-Age” probe sets were identified (ie, for the genes present after validation step 1). This analysis revealed that 52 “Up-with-Age” and 35 “Down-with-Age” GO ontologies were significantly enriched at the significance level of P < .01 (supplemental Table 2).