only 200 - 300 bp long and include 5-10 CpG dinucleotides, the largest span several kbp and involve hundreds of CpGs. These regions tend to occur in clusters and the two genomic areas of high CoRSIV density are observed at the major histocompatibility (MHC) locus on chromosome 6 and at the pericentromeric region on the long arm of chromosome 20.

CoRSIVs are enriched in intergenic and quiescent regions