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In addition to the substantial biological diversity among humans, our limited ability to reliably measure expression changes of small magnitude significantly reduces our capacity to obtain convergent sets of transcriptome data in postmortem brain. In particular, differences in the structure and sensitivity/reproducibility of microarray platforms, and in the variety of tools used to analyze microarray data, strongly influence experimental outcome. In order to better understand the sensitivity, dynamic range, and reproducibility of three common DNA microarray platforms, we compared two human postmortem samples on cDNA microarrays with dual-fluorescence, oligonucleotide GeneChips® (Affymetrix), and single-color gel matrix deposited CodeLink® oligonucleotide arrays. All three microarray platforms reported a good dynamic range and high correlation in replicate experiments, but they failed to consistently identify the same genes as differentially expressed between the same samples. Given their reproducibility and proven accuracy, different microarray platforms appear to be measuring different things by nature of their design and function. This needs to be taken into account when comparing data across studies.

Abstract: The quality of DNA microarray based gene expression data relies on the reproducibility of several steps in a microarray experiment. We have developed a spotted genome wide microarray chip with oligonucleotides printed in duplicate in order to minimise undesirable biases, thereby optimising detection of true differential expression. The validation study design consisted of an assessment of the microarray chip performance using the MessageAmp and FairPlay labelling kits. Intraclass correlation coefficient (ICC) was used to demonstrate that MessageAmp was significantly more reproducible than FairPlay. Further examinations with MessageAmp revealed the applicability of the system. The linear range of the chips was three orders of magnitude, the precision was high, as 95% of measurements deviated less than 1.24-fold from the expected value, and the coefficient of variation for relative expression was 13.6%. Relative quantitation was more reproducible than absolute quantitation and substantial reduction of variance was attained with duplicate spotting. An analysis of variance (ANOVA) demonstrated no significant day-to-day variation. [Copyright &y& Elsevier]