Novel Mutations of the JAK2 Gene and Erythropoietin Receptor Gene in Japanese Chronic Myeloproliferative Diseases.
Authors: Inami Mitsuharu , Yamaguchi Hiroki , Hasegawa Setsuo , Gomi Seiji , Watanabe Ayako , Kosaka Fumiko , Mitamura Yoshio , Kobayashi Ai , Kimura Sayaka , Dan Kazuo , Inokuchi Koiti 
Published: April 2020

Abstract
It is well known that JAK2V617F mutation (JAK2 V617F) is found in many but not all the chronic myeloproliferative disease (CMPD) patients. Many questions remains unsolved in CMPD and JAK2 mutation, such as why a single JAK2 mutation cause different CMPD phenotypes, and what other hits are needed in these diseases. Recently novel JAK2 deletion and mutation were found in CMPD without JAK2 V617F (NEJM2007;356:459–468). Heterozygous mutations in the erythropoietin receptor (EPOR) gene were found in familiar erythrocytosis but not in polycythemia vera (PV). However, these researches were done by single stranded conformation polymorphism (SSCP) method, which has possibility of false-negative compared to direct sequencing. Marine et al. (Cell; 1999;98:617–627) found the homozygous deletion of the suppressor of cytokine signaling (SOCS)-3 gene in mice resulted in embryonic lethality associated with marked erythrocytosis, and increased in vitro proliferative capacity of progenitor cells. These findings encouraged us to analyze gene sequence of the exon 12 and 14 of the JAK2 gene, and whole EPOR, SOCS-3 genes in order to clarify molecular mechanisms of the JAK2 V617F negative CMPD. At first, we performed screening JAK2 V617F among 127 Japanese CMPD patients. JAK2 V617F was positive in 31 PV patients (n=52), 28 ET patients (n=55), 5 CMPD-unclassified patients (n=15) and 1 hyper eosinophillic syndrome patients (n=5). As for PV patients, JAK2 V617F positive rate was 59.6% which was significantly low compared with those of Caucasians. Previous report by Dan et al. (Int J Hematol. 2006;83:443–449) has demonstrated that the clinical features were different between Japanese and Western patients of PV and ET such as low incidences of thrombotic event, hemorrhagic event, transition to acute leukemia, and the rate of chromosome abnormality. These findings remind us of a report by Vannucchi et al. (ASH Annual Meeting Abstracts. 2006;108:5–) that there was a meaningful correlation between the proportion of mutant JAK2 allele and the propensity to a symptomatic disease in PV patients. Next, we performed mutation analyses of the JAK2, EPOR and SOCS-3 genes. In the analysis of the JAK2 exon 12, we found a novel mutation and deletion in a PV patient that had G to A conversion at nucleotide 1621 resulting in substitution of arginine to lysine at amino acid position 541 and had deletion at nucleotide position 1625 to 1630 (E543-D544 deletion) (JAK2R541K E543-D544 del). JAK2 E543-D544 deletion was in the next codon of the deletion in JAK2 exon 12 previously reported. A novel EPOR gene mutation was detected at amino acid position 478 (CCC to CGC) leading to substitution of proline to arginine (EPORP478R) in two ET patients. EPORP478R was located within SOCS binding site, and we speculate that EPORP478R affected SOCS-3 binding ability to EPOR. No SOCS-3 gene mutation was detected. Our study indicates that JAK2R541K E543-D544 del and EPORP478R may contribute to the pathogenesis of CMPD in a subset of JAK2V617F negative patients.