We chose this targeted gene in particular to study since the Apcs gene is located on Chromosome 1, approximately 94 cM from the centromere, within a region where several lupus-susceptibility loci, designated Sle1 (Morel et al. 2001), Nba2 (Drake et al. 1995; Vyse et al. 1997), and Bxs3 (Hogarth et al. 1998; Haywood et al. 2000), have been mapped in NZW, NZB, and BXSB lupus-prone strains, respectively. This evidence concerns the gene APCS and systemic lupus erythematosus.