Studies to date suggest that the main causes of bleeding diatheses in primary MC disease likely include pathological hyperfibrinolysis in MCAD with elevation of tPA levels released in significant amounts also from MCs and endothelial cells as well without concomitant release of plasminogen activator inhibitor type 1 (PAI) [31], decrease of PAI activity and significantly increased plasminogen activation indicated by increased plasmin–antiplasmin (PAP) complexes [17], and increased expression of urokinase-type plasminogen activator (uPA; encoded by the gene PLAU; [34]). This evidence concerns the gene SERPINB2 and medium chain acyl-CoA dehydrogenase deficiency.