3) 血栓性血小板減少性紫斑病

Thrombotic thrombocytopenic purpura

血管内皮細胞で産生され血中に放出されたunusually large VWF multimerは，血小板との結合能が高く容易に血管内血栓を形成するが，ADAMTS13で適度に切断されることにより制御されている．TTPはADAMTS13活性が低下することが病態と強く関連しており，先天性TTPではADAMTS13遺伝子変異が認められ，後天性TTPでは多くの症例でADAMTS13に対する自己抗体が検出される．近年，ADAMTS13活性測定法や自己抗体の解析が進展し，TTPの診断，予後，治療効果の判定に大きく貢献している．

ADAMTS13 cleaves unusually large VWF multimer secreted from vascular endothelial cells into appropriate sizes to control its excessive affinity for platelets involved in the prevention of intravascular platelet thrombi.　ADAMTS13 gene mutations were generally found in congenital TTP and autoantibodies to ADAMTS13 were often detected in many cases of acquired TTP, indicating that TTP is strongly associated with the loss of ADAMTS13 activity.　Recently, new methods for the measurement of ADAMTS13 activity have been developed and analysis of the autoantibodies has been performed, thus contributing greatly to the diagnosis, treatment and prognosis of the disorder.