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Layton MJ, Cross BA, Metcalf D, Ward LD, Simpson RJ, Nicola NA.Layton MJ, et al. Among authors: simpson rj.Proc Natl Acad Sci U S A. 1992 Sep 15;89(18):8616-20. doi: 10.1073/pnas.89.18.8616.Proc Natl Acad Sci U S A. 1992.PMID: 1528870Free PMC article.