SPP1 and systemic lupus erythematosus: In a study of 394 Italian SLE patients and 479 matched controls, a total of 13 single nucleotide polymorphisms (SNPs) in OPN gene were identified (six in the 5′ flanking region, one in intron 3, three in exons 6, 7 and 3 in the 3′-UTR; Table 2) (D’Alfonso et al. 2005).