Serum fetuin-A was higher in female PXE patients with cardiovascular involvement than in the corresponding male group (P <0.05). The fetuin-A polymorphism frequencies did not differ among PXE patients, family members, and blood donors. Conclusion: A deficiency of multidrug resistance-associated protein 6 leads to alteration of circulating sub-

Background: Progressive calcification and fragmentation of elastic fibers are characteristic hallmarks of pseudoxanthoma elasticum (PXE), which is caused by mutations in ABCC6 encoding multidrug resistanceassociated protein 6 (MRP6). Because of the great clinical variability of PXE, secondary genetic risk factors are suspected to exist. We investigated whether SPP1 (secreted phosphoprotein 1; previously OPN, osteopontin) promoter polymorphisms are associated with PXE. Methods: We screened an ϳ2-kb region spanning the theoretical promoter of the SPP1 gene for sequence variations by denaturing HPLC and direct sequencing in 93 PXE patients. Sequence variations with a prevalence >5% were genotyped in 93 age-and sex-matched healthy controls. Statistical and haplotype association analyses were performed using Fisher exact test, PHASE v2.1.1, and Haploview 3.2. Results: Mutational screening revealed 9 different sequence variations. Three SPP1 promoter polymorphisms (c.؊1748A>G, c.؊155_156insG, and c.244_ 245insTG) were significantly more frequent in PXE patients than in 93 age-and sex-matched healthy controls (P corrected < 0.05 each). The odds ratios (95% CI) for PXE among carriers of the 3 alleles were, respectively, 2. 16 (1.34 -3.48), 2.41 (1.51-3.82), and 1.97 (1.23-3.15). Haplotype analysis of 6 SPP1 promoter polymorphisms revealed 1 haplotype to be significantly reduced among