A novel germline <i>JAK2</i> mutation in familial myeloproliferative neoplasms
Authors: Elisa Rumi, Ashot S. Harutyunyan, Ilaria Casetti, Daniela Pietra, Harini Nivarthi, Richard Moriggl, Ciara Cleary, Klaudia Bagienski, Cesare Astori, Marta Bellini, Tiina Berg, Francesco Passamonti, Robert Kralovics, Mario Cazzola
Journal: American Journal of Hematology (2013)

To the Editor Familial clustering of myeloproliferative neoplasms (MPN) has been reported but the molecular basis is still unknown 1, 2. Common mutations involved in the pathogenesis of MPN, such as JAK2, MPL, CBL, and TET2 mutations are mainly somatically acquired also in familial cases 1, 3, 4. Germline mutations underlying familial syndromes resembling MPN have been reported: germline mutations in thrombopoietin (THPO) and thrombopoietin receptor (MPL) gene have been shown to be responsible for hereditary thrombocytosis 5-7. To identify the germline genetic factors that underlie familial clustering of MPN, we applied next generation sequencing with the HiSeq2000 system (Illumina) to our cohort of 61 MPN families. Exome sequencing resulted in the identification of a novel germline JAK2 mutation in a pedigree with assumed diagnosis of familial essential thrombocytemia (ET), as shown in Fig. 1A. The proband (MPC07–116) carried a heterozygous missense mutation (CAT>AAT, chr 9:5073743 (hg19 human genome assembly), C > A) in JAK2 gene, causing a substitution of histidine to asparagine at position 608 (H608N), as reported in Fig. 1B. The analysis of T-lymphocytes revealed that the patient carried a germline H608N JAK2 mutation. The mutation was found also in the other affected family member (58), both in granulocytes and in T-lymphocytes, thus confirming segregation of the JAK2 H608N germline mutation with the disease phenotype. The grandson (MPC07–115), a 17-year-old male, carried the JAK2 H608N germline mutation but he showed a platelet value at the upper limit of normal range (342 × 109/l). Both patients showed isolated thrombocytosis (600 and 648 × 109/l) without splenomegaly and bone marrow fibrosis; no thrombosis occurred during follow-up. All three subjects were heterozygous for the JAK2 46/1 haplotype and did not carry JAK2 V617F or exon 10 MPL mutations. The JAK2 H608N mutation was not found in any affected member of the remaining MPN families. We did not find H608N in any of the public databases (dbSNP135, 1000 Genomes Project, Exome Variant Server) and in a control Italian population of 197 subjects, thus excluding a not annotated single nucleotide polymorphism. To functionally evaluate the effect of the H608N mutation on JAK2 function, we introduced the mutation in the murine Jak2 cDNA by site-directed mutagenesis. We over expressed the wild type and mutant Jak2 constructs in IL-3 dependent Ba/F3 cells and examined the extent of STAT5 phosphorylation at different IL-3 concentrations. As shown in Fig. 2, the H608N mutation resulted in more STAT5 phosphorylation than the wild type Jak2. The novel H608N mutation is mapped in exon 14, as the classic V617F mutation 8. Histidine 608 belongs to the JH2 domain of JAK2 protein, which inhibits the JH1 kinase domain. Mutations affecting the JH2 domain, as H608N, might impair the regulatory function of JH2 and increase the kinase activity. Two cases of hereditary thrombocytosis associated with novel JAK2 germline mutations (R564Q and V617I) have been recently reported 9, 10. According to these previous reports and to our study, it seems that JAK2 germline mutations might account for some cases of familial ET that are indeed hereditary thrombocytosis. The authors thank Roberto Giambruno and Nicole Them for their help with cloning of JAK2 H608N mutation. Elisa Rumi1 Ashot S. Harutyunyan2 Ilaria Casetti1 Daniela Pietra1 Harini Nivarthi2 Richard Moriggl3 Ciara Cleary2 Klaudia Bagienski2 Cesare Astori1 Marta Bellini1 Tiina Berg2 Francesco Passamonti4 Robert Kralovics2,5 Mario Cazzola1 1Department of Hematology Oncology, Fondazione IRCCS Policlinico San Matteo, University of Pavia, Pavia, Italy 2CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna, Austria 3Ludwig Boltzmann Institute of Cancer Research, Vienna, Austria 4Division of Hematology, Department Internal Medicine, A.O. Ospedale di Circolo e Fondazione Macchi, Varese, Italy; 5Department of Internal Medicine I, Division of Hematology and Blood Coagulation, Medical University of Vienna, Vienna, Austria Conflict of interest: Nothing to report.Contract grant sponsor: AIRC [Associazione Italiana per la Ricerca sul Cancro, Special Program Molecular Clinical Oncology 5 per mille (project number #1005)]Contract grant sponsor: Fondazione Cariplo; Regione Lombardia (M.C.); Italian Society of Experimental Hematology (SIES) (E.R.);Italian Ministry of Health for young researchers (E.R.)Contract grant sponsor: Austrian Science Fund (R.K.)Contract grant number: P23257-B12Contract grant sponsor: MPN Research Foundation