The study will be performed on 50 APS (antiphospholipid Syndrome) patients, which will be randomized to receive either CoQ10 (200mg/day) or placebo for one month. Blood will be drawn at time 0 and at the end of the treatment. Studies will be conducted in plasma and purified leukocytes from APS. Design: 1) Study of endothelial function: 2) Analysis of changes operated on various prothrombotic/proinflammatory parameters and their associated intracellular signalling. 3) Analysis of mitochondrial ultra structure and activity; mitochondrial antioxidant system characterization; Expression levels and activity of transcription factors/proteins involved in oxidative stress (Foxo 3, NFkB, Nrf2), Quantification of CoQ10 (Coenzyme Q10). 4) Biomarkers of oxidative stress. 5) miRNAs microarrays, RT-PCR validation and correlation/association studies. 6) Induction of over-expression of miRNAs of interest; luciferase constructs. 7)Studies of methylation.