To determine whether variants that predispose to the development of MPN confer a functional effect on particular aspects of MPN disease features, we correlated genotypes of the top associations with clinical and laboratory measurements and outcome recorded for JAK2V617F-negative patients recruited into the PT-1 trial19 (Supplementary Table 3; absence of correlations with the JAK2 46/1 haplotype has been reported previously10). The gene discussed is JAK2; the disease is myeloproliferative neoplasm.