EEC Growth, JAK2 Mutation, PRV-1 Overexpression and X-Chromosome Inactivation Pattern: Predicting Values on Polycythemia Vera Evolution and Risk of Thrombosis in Idiopathic Thrombocytosis.
Authors: Shih Lee-Yung , Lee Ching-Tai , Lin Tung-Liang , Chang Chia-Hui , Huang Chein-Fuang , Wang Po-Nan , Kuo Ming-Chung , Dunn Po , Wu Jin-Hou , Chang Hung , Lan Yii-Jenq , Tang Tzung-Chih 
Published: October 2019

Abstract
We have previously demonstrated that endogenous erythroid colony (EEC) growth could predict PV evolution in idiopathic thrombocytosis (IT) (Blood 83:744, 1994). We also showed that female patients with IT and monoclonal X-chromosome inactivation pattern (XCIP) had a high risk of vascular complications (Blood100:1596, 2002). Recently, PRV-1 overexpression and JAK2V617F mutation have been described and implicated in the diagnosis of Ph(-) chronic myeloproliferative disorders. In a large cohort of patients with IT, we aimed
to determine the correlation among the molecular markers of EEC growth, JAK2 mutation status, PRV-1 level and XCIP, and to assess the predicting values of these biomarkers on PV evolution and risk of thrombosis.
Allele-specific PCR assay was used to detect JAK2V617F in peripheral blood granulocytes (n=178) or bone marrow cells (n=75) from patients with IT. EEC assay was performed on 235 patients in a serum-free culture system at initial diagnosis. PRV-1 mRNA expression in granulocytes from 187 patients was measured by real-time RQ-PCR assay and expressed as the copy number of PRV-1 normalized to GAPDH gene (NCN). Clonality analysis of XCIP with HUMARA-PCR assay was performed on 123 female patients. JAK2V617F was detected in 57.7% of patients with IT. Forty-one percent of IT patients had EEC growth at initial presentation. Of those analyzed for PRV-1 levels, 138 patients had not received platelet-lowering agents at time of analysis; 72 (38.5%) had PRV-1 overexpression with NCN ≥ 1 (NCN of 30 normal subjects, mean±SE: 0.32±0.04, range: 0.04–0.97). Seventy-six female patients had monoclonal XCIP and 28 had polyclonal XCIP; the remaining 19 patients had ambiguous or homozygous pattern of XCIP. EEC growth was strongly correlated with JAK2 mutation (P<0.0001) and PRV-1 overexpression (P<0.0001). PRV-1 overexpression was highly associated with JAK2 mutation (P<0.0001) and monoclonal XCIP (P=0.003). The frequency of JAK2 mutation or EEC growth was not different between monoclonal and polyclonal XCIP. Thirty-four patients subsequently developed PV (IT-PV), ranging from 1.5 months to 90 months. All 34 IT-PV patients had EEC growth and all but one harbored JAK2 mutation at initial presentation. Patients with IT-PV had a significantly higher frequency of EEC(+) (P<0.0001), JAK2(+) (P<0.0001), and PRV-1(+) (P<0.0001) than those without PV evolution, whereas there was no difference in age (P=0.914) or XCIP (P=0.550) between IT with and without PV evolution. One hundred and sixty-nine patients had all biomarkers of JAK2/EEC/PRV-1 analyzed, 57 patients were JAK2(+)/EEC(+)/PRV-1(+) and 55 were JAK2(-)/EEC(-)/PRV-1(-). Eighteen patients with all 3 biomarkers-positive developed PV later compared with none of patients with all 3 biomarkers-negative (P<0.0001). Eighty-two patients experienced thrombotic complications during their disease courses. The occurrence of thrombosis was strongly associated with EEC growth (P=0.0002), JAK2 mutation (P=0.007), PRV-1 level (P=0.004), and XCIP (P=0.034). The present study showed that EEC growth and JAK2 mutation were predictors of PV evolution; EEC growth, JAK2 mutation, PRV-1 overexpression and monoclonal XCIP predicted the risk of thrombosis in patients with IT.