miRNAs are 21–23 nucleotide long RNAs that post-transcriptionally silence genes or reduce their expression levels by complementarily binding to target sites within mRNAs. More than 29,000 human mRNAs are collectively targeted by are over 2500 miRNAs (Kozomara and Griffiths-Jones, 2014). Several different miRNA binding sites may be present on one mRNA and many contain genetic variations. To date, over 400,000 SNPs have been identified in miRNA binding sites (Liu et al., 2012). Interestingly, only about 32,000 have a minor allele frequency greater than 1% classifying most of them as rare variants (Liu et al., 2012). Thus, tests to identify functional SNPs affecting miRNA binding, here referred to as mirSNPs, will involve screening a large number of variants.
