Finally, although beyond the scope of this review, it is worth indicating that the thrombopoietin receptor, MPL, can have both germline (MPL S505N) and somatic mutations, such as MPL 515K/L/A/R, S505N, and S2O4P, causing an MPN [4,6,90], either ET or PMF, as well as benign mutations, such as MPL Baltimore (K39N) [91]. Here, MPL is linked to myeloproliferative neoplasm.