and noncanonical target sites of 399 human miRNAs.INDELs in miRNA sequences and miRNA target sites. About 18% of known human genetic variants are INDELs (27,28), constituting the second largest class of genetic variants after SNPs. Currently, >400 000 small INDELs have been identified in the human genome (27,28). Intuitively, INDELs may generally be more disruptive than SNPs in the alteration of miRNA targeting, as multiple nucleotides may be inserted in or deleted from the interacting sites. A recent genome-wide analysis of mutations in Drosophila provided evidences indicating that INDELs are more deleterious than SNPs in both coding and noncoding regions (29). Small INDELs altering miRNA sequences and target sites have been associated with human diseases (30). For example, a deletion in the target site of miR-657 has been associated with diabetes (18) and an insertion at miR-122 binding site has been linked to hepatocellular carcinoma (17). The PolymiRTS database now includes small INDELs (1–30 bases long) in miRNA target sites and miRNA sequences for both human and mouse (Table 1).Using context + score to assess polymorphic miRNA–mRNA interactions. In a recent update, TargetScan (31) introduced the context + score for selection of the most favorable target sites for miRNAs. Context
