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Rajagopalan S, Long EO.Rajagopalan S, et al.Proc Natl Acad Sci U S A. 2012 Dec 11;109(50):20596-601. doi: 10.1073/pnas.1208248109. Epub 2012 Nov 26.Proc Natl Acad Sci U S A. 2012.PMID: 23184984Free PMC article.