ESR1 and systemic lupus erythematosus: We think DNA hypomethylation of HERV-E clone 4–1 5’LTR is an indispensable factor that account for the upregulation of HERV-E clone 4–1 mRNA for that upregulation of HERV-E clone 4–1 mRNA mainly exists in SLE while not in some other diseases that involving NFAT1 and ER-α activation.