RESEARCH CEU samples,15 we demonstrated that the majority of repeats in these LCL samples were polymorphic (Table 4). Because the functional models of these repeats are not yet known, various classiﬁcations of the repeat polymorphisms, including ‘low category’ (with relatively low numbers of repeats ‘1/1’) versus ‘other genotypes’ were tested for association with gene expression measured by real-time PCR. No statistically signiﬁcant associations ( p , 0.05) were observed between various repeat genotype classes and gene expression in these LCLs, however. The two top-ranking relationships were identiﬁed in INSR and CLMN when comparing the repeat genotypes between ‘low category’ and ‘others’. Overall, these current ﬁndings do not appear to support a putative role for I1 repeats as a novel class of universal gene regulation mechanism which con- tributes to variation in transcript abundance. Because of the limited number of genes we tested experimentally, however, a much more comprehen- sive investigation might be necessary to conﬁrm ﬁnally whether this relationship is a universal mechanism for other genes. Due to the fact that only approximately 50 per cent of genes are believed to be reliably expressed in the LCLs,15,35 and that gene regulation can be tissue speciﬁc,36 it could be interesting to carry out the same investi- gation in other tissue types, to illustrate the poten- tial role of I1 repeats in gene regulation. Furthermore, since population-level gene expression variation has been observed in humans,15,35,37,38 a future survey, using different human populations, might be also worthwhile for illustrating the relationship between I1 repeats and gene expression. Acknowledgments This Pharmacogenetics of Anticancer Agents Research (PAAR) Group (http://www.pharmacogenetics.org) study was supported by NIH/NIGMS grant U01GM61393. 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