One out of 9 mice in the TRKA alone group developed a myeloproliferative neoplasm, probably due to mild activation of TRKA by its overexpression and/or endogenous murine NGF, while no other animals with TRKA alone, NGF alone or LNGFR showed SM or other hematological malignancies. The gene discussed is NTRK1; the disease is systemic mastocytosis.