Heriditary Predispositions to Myeloproliferative Neoplasms

Familial predispositions to cancer offer a unique opportunity to identify mutations of genes playing important role in initiation of cancer. In our previous studies of sporadic myeloproliferative neoplasms (MPN), we identified a unique collection of 58 pedigrees with familial clustering of MPN that are clinically indistinguishable from sporadic MPN. Familial MPN cases also exhibit increased frequency of other malignancies. As familial MPN allows the employment of specific genetic approaches to identify the germ line disease causing mutations, we plan to study the genetic basis of familial MPN predisposition using the latest genomics approaches. In Specific aim 1 we plan to study the cytogenetic aberrations of familial MPN patients. Familial cancer predispositions are often conferred by heterozygous tumor suppressor mutations inherited in affected families. Somatic loss-of-function mutations (point mutations, deletions, etc.) of the remaining wild type allele initiate clonal cancer growth in heterozygous carriers. Identification of genomic regions with somatic defects in the cancer tissue may pinpoint the position of the germ line mutation that confers cancer susceptibility in the given pedigree. We will perform a high- resolution cytogenetic analysis to identify the somatic lesions in familial MPN and test these loci for segregation in the pedigrees. To identify candidate regions that harbor germ line mutations we will employ both parametric and non-parametric algorithms of linkage analysis (Specific aim 2). We will genotype all pedigree members from the 9 most informative pedigrees and map the segregating genomic regions. We will also employ a population-based approach and perform a whole-genome association analysis including all affected familial cases. In Specific aim 3, we employ the latest high-throughput sequencing technology for mutation discovery and functionally analyze the detected mutations. The regions identified in the various mapping approaches from Aims 1 and 2 will be subjected to thorough analysis utilizing the next generation sequencing technologies. The mutations discovered will be tested for their germ line or somatic origin and functionally validated to be involved in the MPN disease pathogenesis. Significance: Hematopoietic stem cells are under tight control of proliferation and differentiation in order to supply the large number of blood elements required in normal physiology. Disruption of this process by mutations in key regulatory genes leads to pathologic conditions resulting in either deficient or excessive production of blood elements accompanied by frequent leukemic transformation. Familial studies helped to discover a number of key players in growth regulation. Germ line tumor suppressor mutations frequently cause familial clustering of malignancies often with a very specific phenotype. For example, germ line mutations of the tumor suppressor RB1 cause familial retinoblastoma even though somatic RB1 defects are very frequent in many kinds of tumors. We believe the mutation(s) associated with familial MPN may be similar and by studying familial MPN we have the opportunity to identify a new tumor suppressor gene mutation widespread among malignancies other than MPN.

Families with an increased frequency of cancer offer the opportunity to identify the gene defects (mutations) or other genetic factors that initiate cancer or elevate the risk of cancer. Cancers of blood (hematopoietic malignancies) are either chronic or acute, depending on the severity of disease and disease duration. Myeloproliferative neoplasms (MPN) are a group of chronic blood cancers characterized by an elevated production of different types of blood cells, high frequency of thrombosis and bleeding. MPN is an acquired disease in which one hematopoietic stem cell acquires a gene defect that allows the mutated stem cell to outgrow and manifest the disease. Up to 10% of MPN patients have first degree relatives with MPN or have a family history of MPN indicating that hereditary factors influence the disease initiation. In addition, about 5 % of chronic MPN patients transform to acute myeloid leukemia with bad prognosis. Thus, MPN serves as an ideal model disease to study the genetic basis of cancer as it captures the entire disease evolution starting from hereditary predisposition, cancer initiation, chronic phase disease to acute phase disease (leukemia). In this project, we applied modern genetics to identify the underlying genetic defects of MPN and predominantly focused on families where MPN is inherited but also studied MPN occurring without a documented family history (so-called sporadic MPN). We assembled a unique collection of biological material (over 1000 samples) from patients, both familial and sporadic. Our studies of families resulted in the identification of mutations in genes such as JAK2 and RBBP6 that cause MPN directly or elevate the frequency of MPN. We found mutations of RBBP6 in about 5% of pedigrees with MPN and mutations of JAK2 in about 1% of families. We also showed that certain variants of genes (JAK2 and TERT) with a weak effect commonly found in Western populations elevate the likelihood of MPN in carriers of these genetic variants and explain the majority of familial clustering of MPN. Our data indicate that, although the common JAK2 and TERT genetic variants influence the hereditability of MPN, many pedigrees carry rare mutations with a strong effect that alone or in combination with JAK2 and TERT variants are responsible for the familial MPN. Within the current project we identified not only genetic defects in familial MPN but also in sporadic MPN. We compared the mutation type and distribution among the familial and sporadic MPN. Our future research will be directed at those hereditary genetic factors that influence MPN disease complications (such as thrombosis) and influence patients responses to therapy. Understanding the role of hereditary factors in familial MPN not only deepens our understanding of the disease mechanisms but allows the assessment of disease complication risks, as well as to establish the proper diagnosis and to assess the MPN risk in the population. MPN is associated with an increasing age with a mean age at diagnosis of approximately 60 years. In the future decades, MPN will become more frequent in the aging, demographically shifting Western populations. Therefore, a detailed understanding of the pathogenesis, proper diagnosis and cost efficient clinical management of MPN will be increasingly important.