The JAK2 V617F Mutation Identifies Specific Subgroups of Myelodysplastic Syndrome (MDS).

The myelodysplastic syndromes (MDS) encompass a heterogeneous group of clonal stem cell disorders characterised by ineffective erythropoiesis and peripheral blood cytopenias. However, specific subgroups of MDS with both myeloproliferative (MPD) and dysplastic features are recognized, which include chronic myelomonocytic leukaemia (CMML), refractory anaemia with ringed sideroblasts and thrombocytosis (RARS-T) and MDS/MPD unclassified. In addition cases of 5q- syndrome may present with a marked elevation in platelet count and a hypercellular bone marrow. The molecular events which determine the predominant morphological features however remain unclear. The JAK2 somatic point mutation (V617F) results in constitutive activation of the tyrosine kinase and culminates in both proliferation and differentiation signals to the cell and thus may contribute to the proliferative features identified in MDS as reported in the chronic MPDs. We analysed 194 patients from six centres with a diagnosis of MDS or MDS/MPD for the presence of the JAK2 mutation. 11 cases of RA; 70, RARS; 60, 5q- syndrome; 28, refractory anaemia with excess blasts (RAEB); 9, acute myeloid leukaemia with multi-lineage dysplasia (AML-MLD); 4, MDS/MPD-U; 1, CMML; and 1, hypoplastic MDS were analysed. DNA samples were obtained from bone marrow aspirate or peripheral blood. Ethical approval was obtained. Genomic DNA was prepared using standard methods (Qiagen). A modified allele specific PCR (AS PCR) was used to screen DNA samples. JAK2 mutated DNA samples were further subjected to pyrosequencing for confirmatory testing. The median age of the JAK2 mutant versus wild type (WT) cases was 66years (46–80years) v 67years (30–92years). The JAK2 mutation was detected in 13/194 (6.7%) cases overall. 4/70 (5.7%) RARS, 5/60 (8%) 5q- syndrome, 1/28 RAEB (associated with del 5q), 1/4 CMML, 1 MDS/MPD-U and 1/8 AML-MLD demonstrated the mutation. Within the RARS cohort, the prevalence of JAK2 mutation increased to 4/6 (67%) of cases with thrombocytosis (platelets >500x10⁹/l). The presence of the mutation was confirmed in 8/13 cases. In cases analysed, the mutation was detected in CD34+, CD14+, CD15+ and CD61+ cell fractions but not CD3+ or CD19+ cell lineages. On analysis of the haemoglobin (Hb), platelet count and total white cell count (WCC) in the JAK2 mutant versus wild-type groups, there was no difference in median Hb (10.8 v 9.2 g/dl, p=0.275) but a significantly higher median platelet count (526 v 209 x10⁹/l, p<0.001) and WCC (6.43 v 4.84x10⁹/l, P<0.001) was observed in the JAK2 mutant cases. In addition, all JAK2 mutant cases were associated with marked increase in bone marrow cellularity. The JAK2 mutation identifies a subset of MDS patients with proliferative bone marrow morphology and frequent thrombocytosis and leucocytosis. The presence of JAK2 mutation helps to identify a subgroup of MDS patients who may benefit from therapies that specifically target the mutant JAK2.