Clonal hypereosinophilic syndromes There are two broad subtypes of clonal hypereosinophilic syndrome (see table Clonal Hypereosinophilic Syndromes): Myeloproliferative variant Lymphoproliferative variant The myeloproliferative variant is often associated with a small interstitial deletion in chromosome 4 at the CHIC2 site that causes the FIP1L1/PDGFRA - associated fusion gene (which has tyrosine kinase activity that can transform hematopoietic cells). Patients often have Anemia Elevated serum vitamin B12 levels Hypogranular or vacuolated eosinophils Myelofibrosis Splenomegaly Thrombocytopenia Patients with the myeloproliferative subtype often develop endomyocardial fibrosis and may rarely develop acute myeloid leukemia or acute lymphoblastic leukemia.