Arsenic has been linked to epigenetic changes, heritable changes in gene expression that occur without changes in DNA sequence. These include DNA methylation, histone modification, and RNA interference. Studies investigating arsenic as an epigenetic factor is expected to assist in developing precise biomarkers of exposure and susceptibility. (Baccarelli, A.; Bollati, V. "Epigenetics and environmental chemicals". Current opinion in Pediatrics 21 (2): 243–251. (2009) doi:10.1097/MOP.0b013e32832925cc. PMC 3035853. PMID 19663042.) (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3035853)