GAS6 and Pseudoxanthoma elasticum: Since vitamin K-dependent carboxylation of Gas6 favors protein binding to the Axl tyrosine kinase receptors (40), it could be suggested that the decrease in Gas6 levels observed in this study could be related to increased binding and consequently to reduced availability of free Gas6 in serum, further supporting the concept that vitamin-K dependent carboxylation per se is not affected in PXE.