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Assessment of normal variability in peripheral blood gene expression.

Campbell C, Vernon SD, Karem KL, Nisenbaum R, Unger ER.
Assessment of normal variability in peripheral blood gene expression.
Disease Markers 18:201-206, 2002.

Summary

The fluctuation in gene expression levels over time has not been well characterized but must be considered when evaluating peripheral blood, because this type of clinical sample reflects many ongoing systemic processes. Some differences in peripheral blood gene expression may be due to the timing of sample collection in addition to the ongoing disease process. To evaluate the natural periodicity of peripheral blood gene expression, three healthy volunteers were bled three times a day once a week for a month. The gene expression of these 36 samples was assessed using high-density macroarrays. Overall, there was very little inter- or intra- daily variability to indicate any substantial periodicity in peripheral blood gene expression. However, in approximately 1% of genes examined, some fluctuation in gene expression was observed either over the course of the day or from week to week. It is important to realize that while there appears to be no significant changes associated with the time of collection in the majority of genes evaluated in this study, the levels of gene expression for a small subset of genes were shown to fluctuate substantially, indicating the need to control for the time of sample collection whenever possible.

Abstract

Peripheral blood is representative of many systemic processes and is an ideal sample for expression profiling of diseases that have no known or accessible lesion. Peripheral blood is a complex mixture of cell types, and some differences in peripheral blood gene expression may reflect the timing of sample collection rather than an underlying disease process. For this reason, it is important to assess study design factors that may cause variability in gene expression not related to what is being analyzed. Variation in the gene expression of circulating peripheral blood mononuclear cells (PBMCs) from three healthy volunteers sampled three times per day each week for one month was examined for 1,176 genes printed on filter arrays. Less than 1% of the genes showed any variation in expression that was related to the time of collection, and none of the changes were noted in more than one individual. These results suggest that observed variation was due to experimental variability.

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