Myelodysplastic syndrome with thrombocytosis in a patient with Klinefelter's syndrome.

We report herein a patient with Klinefelter's syndrome associated with refractory anemia with excess of blasts in transformation, a subtype of myelodysplastic syndrome (MDS). The MDS developed with karyotypic abnormality involving t(4;7)(q21;q11), and was characteristic of marked thrombocytosis and marrow infiltration by many atypical megakaryocytes. The patient also had diabetes mellitus and a disturbed immune system. To our knowledge, this is the fifth reported case of MDS in patients with Klinefelter's syndrome in the literature.