aHUS: a disorder with many risk factors.

disorder. Only highly qualified centers where more specific tests are available may take on the task of further evaluation. The platelet physiology subcommittee of the International Society of Thrombosis and Haemostasis (ISTH) has dedicated its work during recent years to searching for ways to improve and standardize platelet function testing, applying platelet aggregometry, the PFA-100 device, and a proteomics approach.2-4 This report also raises the issue of the gap between genotype and phenotypic expression in hereditary diseases. The D304N substitution was observed in the index patient, who presented with mild bleeding symptoms, and in his father, who had no history of bleeding. As in other cases, a search for modifier genes and for other factors might shed light on this differential phenotypic expression. Thus, the genetic background of a disease does not always explain all phenotypes, and a search for genetic and environmental modifiers should be considered for a more comprehensive understanding of this entity. Improved understanding of the complex, multiple pathways of platelet activation is significantly contributing to the development of new antiplatelet drugs. Antiplatelet drug therapy is currently undergoing a dramatic revolution, including novel observations on platelet drug resistance, more refined dose adjustment, and development of more potent and safer new drugs.5 One such example is the development of new TxA2 R inhibitors. Such inhibitors are potentially more effective than aspirin because of their inhibitory effect on endothelial cell TxA2 R as well. Acknowledgment: The author thanks Dr D. Rund for helpful suggestions. Conflict-of-interest disclosure: The author declares no competing financial interests. ■