FAMILIAL ESSENTIAL THROMBOCYTHEMIA - CLINICAL CHARACTERISTICS OF 11 CASES IN ONE FAMILY

Reports on familial occurrence of essential thrombocythemia (ET) are s canty. Many clinical and hematological aspects of familial ET have not been clarified yet. We studied 16 family members in four successive g enerations. By laboratory tests and bone marrow examination they were divided into a non-thrombocythemia group (n = 5) and into ET patients (n = 11). Five ET patients were asymptomatic, three patients had both vaso-occlusive and hemorrhagic symptoms, and three patients only vaso- occlusive symptoms. The platelet count ranged from 500 to 1700 x 10(9) /l. Symptoms correlated with age but not with platelet count. ADP-indu ced platelet aggregation distinguished best between patients and non-E T subjects. Four patients and four non-ET subjects had factor VIII:C o r von Willebrand factor antigen abnormalities; all but one had blood g roup O. These abnormalities were not due to inherited von Willebrand's disease according to haplotype analysis. Two patients and three non-E T subjects had a bleeding diathesis. One of these two patients and all . three non-ET subjects had a decreased factor VIII:C or vWF:Ag. No ch romosome abnormalities were found. In conclusion, familial. ET has a r elatively benign course with clinical manifestations similar to nonfam ilial cases, and it is probably transmitted by an autosomal dominant m ode of inheritance.