SOD1 and pseudoxanthoma elasticum (inherited or acquired): Apart from perturbation of the vitamin K cycle, a significant upregulation of superoxide anions (O2−) production and mitochondrial superoxide dismutase (Mn-SOD) activity as well as an increase in the extracellular SOD (EC-SOD) concentration was found in PXE fibroblasts compared to controls, which can be linked to increased oxidative stress.