Juvenile myelomonocytic leukemia (JMML) with the hematologic phenotype of severe beta thalassemia.

A 3-year-old Filipino-American child with recurrent fever, splenomegaly, anemia, and thrombocytopenia, was found to have a hemoglobin F level of 76.9%. His reticulocyte count was elevated (4.3%), and erythroblasts were present in his peripheral blood. The child's erythrocytes were microcytic (MCV 66.9 fl) but his serum ferritin level was normal. His bone marrow at initial presentation demonstrated normal cellularity without an increase in blast cells. The disease progressed with worsening anemia, leukocytosis, and thrombocytopenia, with increased blasts in his marrow and the appearance of a mediastinal mass. His liver, spleen, and lymph nodes were found to be infiltrated with myeloblasts, supporting a diagnosis of juvenile myelomonocytic leukemia (JMML). Analysis of the child's Hb F showed a Ggamma/Agamma ratio of 2.2, which was within the characteristic range for JMML. A globin synthesis study using blood reticulocytes showed an alpha/non-alpha globin synthesis ratio of 2.24, typical of severe homozygous beta thalassemia. Southern blot analysis of blood-leukocyte DNA from the patient and his parents demonstrated no apparent abnormality in the beta-globin gene promoter or coding regions. The elevated level of Hb F in this child with JMML appeared to be part of an acquired Cooley's anemia-like hematologic phenotype.