Inherited susceptibility for thrombosis in MPN

Myeloproliferative neoplasms (MPN) are a group of chronic blood cancers (hematopoietic malignancies) characterized by elevated production of different types of blood cells. Thrombosis is a major complication in MPN that significantly contributes to disease morbidity and mortality. MPN-associated thrombosis is known to be influenced by genetic factors. To dissect the role of inherited genetic factors in MPN clinical complications, we have performed genome-wide association studies (GWAS). Association studies test whether the frequencies of certain genetic polymorphisms (variants) differ significantly between cases (MPN patients with clinical event) and controls (MPN patients without clinical event). Our studies attempt to identify genetic variants common in the population that influence the risk of clinical complications of MPN such as blood clotting in the heart or brain (arterial thrombosis). Our previous work revealed a haplotype (set of linked genetic variants) on chromosome 6 to confer increased risk for arterial thrombosis in MPN patients. Moreover, we could demonstrate that presence of the chromosome 6 risk factor influences the regulation of the neighboring TULP4 gene. This risk factor controls to which degree the TULP4 gene is turned on. Experimental data indicate that individuals carrying the chromosome 6 risk factor are likely to have lower amounts of the Tulp4 protein in blood progenitor cells. Here we propose an expansion of genetic association studies on thrombosis in MPN together with a full clinical and functional workup of the chromosome 6 (TULP4) risk factor and other new risk factors we may identify. We will increase both the number of patients in the study and the density of genetic markers (tested variants) across all the human chromosomes. Identified risk genes will be characterized in-depth for epidemiological and clinical parameters. Identification of genetic risk factors for thrombosis in MPN has a high potential to improve the clinical management of MPN in such a way that the clinicians will be able to know at the time of diagnosis which patients have the highest risk for stroke or myocardial infarction. Complete understanding of the biological mechanisms underlying these risk factors is essential for designing new strategies for drug development.

Myeloproliferative neoplasms (MPN) are a group of chronic blood cancers (hematopoietic malignancies) characterized by elevated production of different types of blood cells. Thrombosis is a major complication in MPN and it is known to be influenced by genetic factors. Our previous work based on genome-wide association studies (GWAS) revealed a haplotype (set of linked genetic variants) on chromosome 6 to confer increased risk for arterial thrombosis (blood clotting in the heart or brain) in MPN patients. Moreover, we could demonstrate that presence of the chromosome 6 risk factor influences the regulation of the neighboring TULP4 gene. Experimental data indicate that individuals carrying the chromosome 6 risk factor are likely to have lower amounts of the Tulp4 protein in blood progenitor cells. We proposed an expansion of genetic association studies on thrombosis in MPN together with a full clinical and functional workup of the chromosome 6 (TULP4) risk factor. To achieve that, we attempted to replicate the genetic association in additional independent MPN patient cohorts from several international MPN centers. While the association was present in two cohorts from Austria and Italy, we did not observe the association in three other patient cohorts from Hungary, Japan and the USA, indicating that environmental factors and/or center-specific treatment strategies might impact on the genetic association. Genetically modified mouse models provide the possibility to study gene function in an unbiased way, as environmental influences or other confounding factors can be controlled for. Therefore, we generated a knockout mouse model lacking the TULP4 gene. Comparing TULP4 deficient mice with their genetically unmodified (wild-type) siblings (littermates), we found several lines of evidence for TULP4 potentially influencing risk for thrombosis through developmental, immunomodulatory and metabolic ways. The latter is reflected in an obesity phenotype observed in female TULP4 knock-out mice. As none of this evidence is fully conclusive with regards to thrombophilia, further experiments are planned to be carried out as follow-up projects beyond the FWF funding period. Interestingly, independently of the proposed experiments centered on MPN thrombosis, we observed that mice lacking both paternal and maternal copies of the TULP4 gene are not viable. We further investigated the cause of this embryonic lethality by applying state-of-the-art microscopy based three-dimensional imaging technologies in combination with classical histopathological methods. This allowed us to identify potentially lethal malformations, predominantly concerning the cardiovascular system. While there is currently no conclusive link between those developmental defects and MPN thrombosis, we have designed follow-up experiments to address potential causal relationships. Complete understanding of the biological mechanisms underlying genetic risk factors is essential for designing new strategies for drug development. Based on our in vivo findings we established follow-up projects that will exploit the Tulp4 knockout mouse models beyond the FWF funded period.