Molecular Genetics of Myeloproliferative Neoplasms

Contact/Address

Department of Internal Medicine III
University Hospital of Ulm
Albert-Einstein-Allee 23
89081 Ulm
Germany
Phone: +49-(0)731-500-45521
Fax: +49-(0)731-500-45525

Technicians

Susanne Kuhn

(A) Molecular diagnosis of Myeloproliferative Neoplasms (MPN)

Myleoproliferative Neoplasms (MPN) comprise Various chronic leukemias with myeloid origin. Among them, the molecular cause of chronic myeloid leukemia (CML) is defined most precisely. Typical CML is represented by the activating tyrosine kinase fusion protein BCR-ABL that results from the recurrent chromosome translocation t(9;22). At diagnosis, the most frequent BCR/ABL fusion transcripts that occur in CML (e1a2, b2a2 and b3a2) are detectable by Reverse transcriptase- (RT-) Multiplex-PCR. In the course of disease, Minimal residual disease- (MRD-) monitoring is predictive for the clinical outcome. Therefore, internationally standardized PCR assays are used to monitor response in BCR-ABL positive CML patients under tyrosine kinase inhibitor treatment.

More recently, genetic alterations were also identified in BCR/ABL negative MPN. In particular, the activating JAK2 V617F point mutation has improved the understanding of BCR-ABL negative MPN. In 2005, JAK2 V617F has been discovered as a single-site, clonal, gain-of-function mutation in myeloid cells in the majority of patients with Polycythemia vera (PV, >95%), Essential thrombocythemia (ET, 50-60%) and primary myelofibrosis (PMF, 60%). Though less frequent, JAK2 Exon 12 mutations (e.g JAK2 K539L) occur in V617F negative PV patients, and the MPL W515L/K point mutation is present in about 5%-10% of PMF and ET patients, respectively. In 2013, frameshift mutations in the CALR gene have been described in 20-30% of ET-and PMF patients, now allowing to prove clonality in the vast majority MPN cases since CALR mutations occur mutually exclusive from JAK2 and MPL. Furthermore, the FIP1L1-PDGFRA fusion gene and the KIT D816V mutation are detectable in a subset of patients suffering from Hypereosinophilic syndrome (HES) and Systemic mastocytosis (SM), respectively. For molecular based detection of the above mentioned genetic alterations, PCR-based analyses are applied.

(B) Clinical impact of the JAK2 V617F mutation

In the mouse model, JAK2 V617F leads to a myeloproliferative phenotype resembling PV with marked elevation of erythrocytes and granulocytes. To date, little is known on the pathogenic value of JAK2 V617F in ET and PMF. In addition, it is controversially discussed whether the mutations are relevant for the clinical course by increasing the risk of vascular events, secondary myelofibrosis or transormation into acute myeloid leukemia. The aim of our study is to analyze a large cohort of clinically well-defined MPN patients for the presence of JAK2 V617F. Moreover, the proportion of the mutant allele (homozygous vs. heterozygous) is determined in JAK2 V617F mutated patients by quantitative Real-time PCR. Samples from primary diagnosis and during follow-up (3-6 months intervals) are analyzed prospectively to explore the evolution and prognostic impact of JAK2 V617F in ET, PV and PMF by correlating clinical and molecular data. In addition, JAK2 V617F is used as a marker for sensitive minimal residual disease (MRD) monitoring in patients showing a decline of the allele burden under treatment (e.g. under Interferon-α or after allogeneic stem cell transplantation).

(C) Detailed genomic characterization of MPN

Recent findings show that a subset of MPN patients harbor various other mutations in genes that have been implicated in leukemogenesis (e.g. TET2, DNMT3A or ASXL1). In contrast to JAK2, MPL or CALR, these mutations are less specific for MPN as they also occur in MDS and AML patients. However, these findings reflect the genomic complexity of MPN and are likely relevant for the heterogeneous clinical course as well as for disease evolution. We therefore screen clinically well-defined MPN patient cohorts using modern molecular techniques such as high-resolution ´single nucleotide polymorphism´ (SNP) arrays and ´Next-Generation-Sequencing´ for detailed genomic characterization beyond JAK2, MPL or CALR. These data allow links between the molecular basis and the clinical phenotype by correlating genetic and patient data. In addition, novel hot spot regions harboring candidate genes can be identified serving as a starting point for further functional studies using cell culture and siRNA techniques.

• Cell isolation techniques (Ficoll Paque® centrifugation, MACS® Cell Separation)
• DNA/RNA preparation
• PCR techniques including quantitative Real-time PCR (QuantStudio™, LightCycler®)
• Sanger sequencing and software-supported analyses
• GeneScan™-based mutation screening (Applied Biosystems®)
• High-resolution SNP array analysis (Affymetrix®)
• Next-generation sequencing' (NGS) on HiSeq™ and MiSeq™ (Illumina)

• Else Kröner-Fresenius Stiftung

Representative publications can be found in the entire list of publications.

• Prof. Christine Chomienne, Hopital Saint Louis, Paris, France

• Prof. Nicholas Cross, Wessex Regional Genetics Laboratory, Salisbury, UK

• Prof. Anthony Green, University of Cambridge, Cambridge, UK

• Prof. Ruben Mesa, Mayo Clinic, Scottsdale/Arizona, USA

• Prof. Heike Pahl, University Hospital Freiburg, Center for Clinical Research, Freiburg, Germany