The molecular pathogenesis of myeloproliferative neoplasms

Myeloproliferative neoplasms (MPNs) are a heterogeneous group of haematological stem cell<br/>malignancies characterised by proliferation of one or more cells of the myeloid lineage. The molecular<br/>investigation of MPN was revolutionized in 2005 by the finding that approximately 95% of cases with<br/>polycythaemia vera (PV) and 50-60% of cases of essential thrombocythaemia (ET) and primary<br/>myelofibrosis (PMF) are characterised by a single acquired mutation, JAK2 V617F. My study has<br/>focused on four principal areas:<br/><br/>(i) Involvement of V617F in other myeloid disorders. After developing sensitive methods to<br/>detect and quantify V617F, this mutation was identified in 17% of cases of atypical chronic myeloid<br/>leukaemia (17/99) as well as other atypical MPN, thus demonstrating that it was more widely<br/>involved in myeloid disorders that initially thought. Homozygosity of V617F was shown to have arisen<br/>by acquired uniparental disomy (UPD) and examination of two cases with V617F plus either KIT<br/>D816V or BCR-ABL demonstrated that the mutations had arisen in independent clones.<br/><br/>(ii) In vitro assays to predict imatinib sensitivity. Haemopoietic colony and liquid cultures were<br/>used to determine if peripheral blood or bone marrow cells from atypical MPN cases (n=200) were<br/>sensitive to imatinib. Of those that responded in one or both cultures (n=185) some had known<br/>abnormalities of PDGFRA or PDGFRB, but a significant minority proved negative for all molecular tests<br/>suggesting the presence of uncharacterised imatinib-sensitive mutations.<br/><br/>(iii) V617F as a marker of response to therapy. JAK2 V617F was used as a molecular marker to<br/>monitor the response of PV patients (n=21) to therapy with imatinib and interferon-?. Neither<br/>therapy eradicated V617F but there was a modest reduction in %V617F which correlated with<br/>haematological response. By contrast, in those patients that did not respond (n=13) the %V617F<br/>marginally increased.<br/><br/>(iv) Genetic predisposition to MPN. Whilst investigating the possible contribution of JAK2 single<br/>nucleotide polymorphisms to the phenotypic diversity associated with V617F, marked skewing of<br/>alleles associated with the mutation was observed. Further investigation revealed that V617Fassociated<br/>disease is strongly associated with a specific constitutional JAK2 haplotype, designated<br/>46/1, in all three disease entities compared to healthy controls (PV, n=192, P=2.9x10-16; ET, n=78,<br/>P=8.2x10-9 and MF, n=41, P=8.0x10-5). Furthermore, allele-specific PCR demonstrated that V617F<br/>specifically arises on the 46/1 allele in most cases. The 46/1 JAK2 haplotype thus predisposes to the<br/>development of V617F associated MPNs (OR=3.7; 95% CI 3.1-4.3) and provides a model whereby a<br/>constitutional genetic factor is associated with an increased risk of acquiring a specific somatic<br/>mutation.

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2010

Author dc:creator

• Jones, Amy Victoria

Advisor dc:contributor.advisor

• Cross, Nicholas