PBX1 and systemic lupus erythematosus: Pre-B-cell leukemia homeobox 1 (Pbx1)-d, an isoform of Pbx1, is a dominant negative mutation located in murine NZM2410 lupus susceptibility locus Sle1a1, with a deletion of DNA binding exon 6 and Hox binding exon 7 [40].