| Summary: | Very rare, peculiar congenital bleeding disorders are usually dealt with in clinics without giving much importance. We think that this practice is not correct since the disorders may often provide useful information about blood coagulation. In this review, we assess very rare bleeding conditions. We refer to the defects of the fibrinolytic system, alpha 1-antitrypsin Pittsburg, few dysprothrombinemias, east Texas or short FV defect, FIX Padua, and thrombomodulin (TM) abnormality. These defects are usually not included in rare bleeding disorders. Patients were gathered from two sources: personal files and two time-unlimited PubMed searches carried out on February 2010 and July 2019. Combined defects were disregarded. These rare bleeding conditions are often unrecognized even though some of them, such as antiplasmin deficiency, are not that rare with more than 30 cases reported already. The underevaluation of the fibrinolytic defects is due to the decrease in the use of methods capable of detecting increased fibrinolysis in routine laboratory study. The limited use of immunological tests represents a second drawback as in the dysprothrombinemia, east Texas Factor V, and FIX Padua. Finally, the limited use of assays of natural inhibitors such as tissue factor pathway inhibitor and TM has played a role in delaying east Texas FX recognition and TM defect. The study of rare, peculiar bleeding disorders has been very important in clarifying the nature of the defects, and it has even allowed the identification of mutations that may turn them from prohemorrhagic to prothrombotic in some of these proteins. This has greatly contributed to the understanding of the complex relationship existing among clotting defects. [JBCGenetics 2020; 3(2.000): 84-93]
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