1 Laboratory of Clinical Epidemiology, IRCCS Policlinico S. Matteo, Pavia, Italy; 2 Laboratory of Biotechnology, IRCCS Policlinico S. Matteo, Pavia, Italy; 3 Transplant Research Area, IRCCS Policlinico S. Matteo, Pavia, Italy; 4 Unit of Clinical Immunology, Immunohematology, and Transfusion Service, IRCCS Policlinico S. Matteo, Pavia, Italy; 5 Department of Pathology, IRCCS Policlinico S. Matteo, Pavia, Italy; 6 Department of Hematology, Ospedale Careggi, Florence, Italy and 7 Unit of Internal Medicine, IRCCS Policlinico S. Matteo, Pavia, Italy.
An aberrant tyrosine kinase signalling due to non-receptor tyrosinekinase JAK2 V617F mutation has been highlighted in the pathogenesisof polycythemia vera (PV). In myelofibrosis with myeloid metaplasia(MMM) this mutation has been reported to be present in approximately50% of the patients and its pathogenetic role is not elucidated.Here we report the results of JAK2 V617F mutation in a retrospectiveanalysis of blood samples from 170 patients with MMM. Searchfor JAK2 mutation was performed by an allele specific PCR fromDNA purified from granulocytes. To evaluate whether the mutationwas carried in the homozygous or heterozygous state, digestionof PCR products with BsaXI restriction enzyme was performed.The overall frequency of JAK2 V617F mutation was 60% and homozygosityfor the mutation was found in 39.2% of mutant samples. Diseaseduration was similar in JAK2 mutated and wild type patients.Patients who harboured an homozygous mutation had an highermyeloproliferative severity score (that indexed leukocytosis,thrombocytosis and splenomegaly) than patients who had a wildtype or heterozygous genotype. In post-PV MMM, the mutant genewas present in 22/22 (100%) of patients, and the frequency ofhomozygosity was 59% of the mutated cases. In post-ET MMM (n=13),the mutant gene was present in 46% of the patients, and thefrequency of homozygosity was 16% of the mutant samples. Inidiopathic MMM (n=135), the incidence of the mutational statewas 54.8%, with 35.1% of homozygote mutation. Patients who hadreceived a diagnosis of prefibrotic myelofibrosis (WHO classification)had an incidence of the mutation significantly lower than patientswho were diagnosed in the fibrotic stage (6/18, 33% vs 68/112,60.7%; P=0.001). By considering only patients not receivingcytoreductive or disease modifying agents, patients who hadan heterozygote mutation, had a mean Hb value higher than wildtype patients (9.4 g/dL vs. 11.4 g/dL; P=0.004). Moreover, patientswho had an homozygote mutation had the myeloproliferative severityscore higher than both heterozygote and wild type patients (2.26vs 1.59, P=0.008, and 2.26 vs.1.52, P=0.001, respectively).We conclude that JAK2 V617F mutation is significantly representedin MMM patients. It is a necessary event in the transformationfrom PV to MMM while not in the transformation from ET to MMM.Patients who harboured an heterozygote state maintained higherHb values than patients with a wild type genotype, while thehomozygote mutation was associated with leukocytosis, thrombocytosisand splenomegaly.