MPL and myeloproliferative neoplasm: Since JAK2 mutations observed in MPN patients are known to exert their effects by activating downstream signaling pathways leading to the activation of target genes, it is possible that the effects of all types of mutations observed in JAK2 and other functionally related genes, such as myeloproliferative leukemia virus oncogene (MPL), funnel into the activation of a common set of genes.