If the lack of MRP6-transport activity for certain antioxidants were the cause of oxidative stress and subsequent impairment in the assembly of the extracellular matrix, one would expect even greater damage in tissues with high MRP6 concentrations, which is obviously not the case.
Characterization of the drug resistance and transport properties of multidrug resistance protein 6 (MRP6, ABCC6).
Loss of ATP-dependent transport activity in pseudoxanthoma elasticumassociated mutants of human ABCC6 (MRP6).
This subgroup contains PXE patients most likely to have either no MRP6 protein or no functional MRP6.
In the present study, we evaluated the association between serum fetuin-A, calcium and phosphate, and the PXE phenotype to investigate the link between an absence or functional insufficiency of MRP6 and mineralization of elastic fibers in PXE.
The disorder is caused by mutations in the ABCC6 gene, which encodes for MRP6, a transmembrane transporter with an as yet unidentified function.
To determine the link between MRP6 and the pathologic calcification in PXE, we investigated the production of fetuin-A in PXE patients.
The frequencies of the p.T242M and p.T256S polymorphisms did not differ among PXE patients, relatives, and controls; we therefore conclude that the difference in fetuin-A concentrations results from MRP6 deficiency and not from a genetic background.
(47) suggested that MRP6 fulfills multiple functions in different tissues.
We have not yet determined whether the lower fetuin-A concentrations are a result of impaired MRP6 transport or just secondary to progressive calcification.