XYY male with essential thrombocythemia in childhood

We describe a boy with XYY male accompanied with essential thrombocythemia. This is, to our knowledge, the first complete case report of the kind in t he pediatric literature. The patient was asymptomatic, but at age 5 his pla telet count had increased to 145.5 x 10(4)/mu L, and he was diagnosed as ha ving essential thrombocythemia based on the diagnostic criteria of the Poly cythemia Vera Study Group. At that time, it was discovered by chromosome an alysis of both bone marrow and peripheral blood cells that he was XYY male. At times during the clinical course when his platelet count was 94.1 x 10( 4)/mu L, his serum thrombopoietin (measured by enzyme-linked immunosorbent assay) was 1.09 fmol/mL, which was normal for his age. Aspirin was administ ered, and he remained asymptomatic throughout the course. After 2 years, he underwent a spontaneous remission. Because of the small number of reported cases, we have been unable to determine the relation between XYY males and essential thrombocythemia. (C) 2000 The Japanese Society of Hematology.