Recently, the fusion gene FIP1L1/PDGFRA was found in the long arm of chromosome 4 and its expression has been shown to be associated with development of a clinical hypereosinophilic syndrome (HES) in a significant proportion of patients.     ///    "FIP1L1/PDGFR?, the product of the gene FIP1L1/PDGFRA, is a constitutively activated tyrosine kinase and can be inhibited by imatinib mesylate. "