Other more rarely seen genetic aberrations in MPN are mutations in the myeloproliferative leukemia virus (MPL; thrombopoietin receptor (TPOR)) gene resulting in a substitution of tryptophan at position W515 by leucine (MPLW515L) or lysine (MPLW515K) [12,13]. The gene discussed is MPL; the disease is myeloproliferative neoplasm.