Gene Expression Profiling Defines a Set of New Molecular Markers for Sporadic and Familial Myeloproliferative Disorders.

The description of new molecular markers, such as PRV-1, has revived the interest in myeloproliferative disorders (MPD). To gain information on gene expression in cells derived from the MPD clone, we performed Affymetrix U133A microarray analysis on granulocyte RNA from MPD patients and healthy controls. Granulocytes are relevant for expression profiling in MPD, because they originate from the MPD stem cell clone in all PV, IMF, and in a proportion of ET patients. By analyzing 10 patients with PV, 9 patients with ET and 6 healthy controls we identified more than 300 genes with a significantly altered expression (P<0.05). Both PV and ET samples were clearly separated from healthy controls in unsupervised cluster analysis. The expression profiles of PV and ET showed partial overlap. In addition, we analyzed 4 affected individuals from 3 unrelated families with hereditary MPD-like phenotypes. Interestingly, 2 affected individuals from the same family with a PV-like phenotype clustered with the sporadic PV group, whereas 2 patients with familial ET-like phenotype had an expression profile closely resembling sporadic ET. Together with our finding that the family with PV displays clonal hematopoiesis, these results support the concept that studying familial MPDs, i.e. positional cloning of the mutated genes, could be relevant to advancing our understanding of sporadic MPD. From the 300 genes which displayed altered expression in MPD patients, we selected 15 for a detailed quantitative PCR analysis in a Swiss cohort of 42 MPD patients, 3 patients with chronic myelogenous leukemia, 7 patients with secondary erythrocytosis and 14 healthy controls. These markers include genes encoding transcription factors (KLF4, ETS2), a growth factor (FGF13) and proteins involved in signaling (SOCS3, FYB). A combination of three markers (HP, HRP, and ETS2) was sufficient to detect all PV patients that displayed endogenous erythroid colonies, including PV patients with normal levels of PRV-1. MPD patients with a history of complications, such as bleeding, secondary fibrosis or leukemic transformation, exhibited significantly higher levels of expression in a subset of these markers. In contrast, there was no difference in expression levels between MPD patients who received hydroxyurea and patients without cytoreductive treatment, suggesting that hydroxyurea does not alter the phenotypic characteristics of the MPD clone. We are now validating the usefulness of these markers on an independent test cohort of 93 individuals from Italy. The conclusions from this comparison will be presented.