Human mortalin (HSPA9): a candidate for the myeloid leukemia tumor suppressor gene on 5q31

Identification of Biomarkers Affecting Cryopreservation Recovery Ratio in Ram Spermatozoa Using Tandem Mass Tags (TMT)-Based Quantitative Proteomics Approach

Sperm proteins play vital roles in improving sperm freezing resilience in domestic animals. However, it remains poorly defined which proteins regulate the freezing resilience of spermatozoa in rams (Ovis aries). Here, we compared the proteome of ram sperm with a high cryopreservation recovery ratio (HCR) with that of ram sperm with a low cryopreservation recovery ratio (LCR) using a tandem mass tag-based quantitative proteomics approach. Bioinformatic analysis was performed to evaluate differentially expressed proteins (DEPs). A total of 2464 proteins were identified, and 184 DEPs were screened. Seventy-two proteins were higher in the LCR group. One hundred and twelve proteins were more abundant in the HCR group, and they were mainly involved in the regulation of oxidative phosphorylation and thermogenesis pathways. Proteins in high abundance in the HCR group included the S100A family, such as S100A8, S100A9, S100A14, and S100A16, effectively controlling for CA²⁺ and maintaining flagella structure; HYOU1 and PRDX1, which participate in antioxidant protection and anti-apoptosis to prevent cell death; and HSP90B1, which maintains cell activity and immune response. Our results could help illuminate the molecular mechanisms underlying cryopreservation of ram semen and expand the potential direction of cryopreservation of high-quality semen.

Abrogating the Interaction Between p53 and Mortalin (Grp75/HSPA9/mtHsp70) for Cancer Therapy: The Story so far

p53 is a transcription factor that activates the expression of a set of genes that serve as a critical barrier to oncogenesis. Inactivation of p53 is the most common characteristic in sporadic human cancers. Mortalin is a differentially sub-cellularly localized member of the heat shock protein 70 family of chaperones that has essential mitochondrial and extra-mitochondrial functions. Elevated mortalin levels in multiple cancerous tissues and tumor-derived cell lines emphasized its key role in oncogenesis. One of mortalin’s major oncogenic roles is the inactivation of p53. Mortalin binds to p53 sequestering it in the cytoplasm. Hence, p53 cannot freely shuttle to the nucleus to perform its tumor suppressor functions as a transcription factor. This protein-protein interaction was reported to be cancer-specific, hence, a selective druggable target for a rationalistic cancer therapeutic strategy. In this review article, the chronological identification of mortalin-p53 interactions is summarized, the challenges and general strategies for targeting protein-protein interactions are briefly discussed, and information about compounds that have been reported to abrogate mortalin-p53 interaction is provided. Finally, the reasons why the disruption of this druggable interaction has not yet been applied clinically are discussed.

Mitochondrial chaperones in human health and disease

Molecular chaperones are a family of proteins that maintain cellular protein homeostasis through non-covalent peptide folding and quality control mechanisms. The chaperone proteins found within mitochondria play significant protective roles in mitochondrial biogenesis, quality control, and stress response mechanisms. Defective mitochondrial chaperones have been implicated in aging, neurodegeneration, and cancer. In this review, we focus on the two most prominent mitochondrial chaperones: mtHsp60 and mtHsp70. These proteins demonstrate different cellular localization patterns, interact with different targets, and have different functional activities. We discuss the structure and function of these prominent mitochondrial chaperone proteins and give an update on newly discovered regulatory mechanisms and disease implications.

Investigating protein patterns in human leukemia cell line experiments: A Bayesian approach for extremely small sample sizes

Human cancer cell line experiments are valuable for investigating drug sensitivity biomarkers. The number of biomarkers measured in these experiments is typically on the order of several thousand, whereas the number of samples is often limited to one or at most three replicates for each experimental condition. We have developed an innovative Bayesian approach that efficiently identifies clusters of proteins that exhibit similar patterns of expression. Motivated by the availability of ion mobility mass spectrometry data on cell line experiments in myelodysplastic syndrome and acute myeloid leukemia, our methodology can identify proteins that follow biologically meaningful trends of expression. Extensive simulation studies demonstrate good performance of the proposed method even in the presence of relatively small effects and sample sizes.

Identification of Arsenic Direct-Binding Proteins in Acute Promyelocytic Leukaemia Cells

The identification of arsenic direct-binding proteins is essential for determining the mechanism by which arsenic trioxide achieves its chemotherapeutic effects. At least two cysteines close together in the amino acid sequence are crucial to the binding of arsenic and essential to the identification of arsenic-binding proteins. In the present study, arsenic binding proteins were pulled down with streptavidin and identified using a liquid chromatograph-mass spectrometer (LC-MS/MS). More than 40 arsenic-binding proteins were separated, and redox-related proteins, glutathione S-transferase P1 (GSTP1), heat shock 70 kDa protein 9 (HSPA9) and pyruvate kinase M2 (PKM2), were further studied using binding assays in vitro. Notably, PKM2 has a high affinity for arsenic. In contrast to PKM2, GSTP1and HSPA9 did not combine with arsenic directly in vitro. These observations suggest that arsenic-mediated acute promyelocytic leukaemia (APL) suppressive effects involve PKM2. In summary, we identified several arsenic binding proteins in APL cells and investigated the therapeutic mechanisms of arsenic trioxide for APL. Further investigation into specific signal pathways by which PKM2 mediates APL developments may lead to a better understanding of arsenic effects on APL.

Submicroscopic deletion of 5q involving tumor suppressor genes (CTNNA1, HSPA9) and copy neutral loss of heterozygosity associated with TET2 and EZH2 mutations in a case of MDS with normal chromosome and FISH results

Advances in genome-wide molecular cytogenetics allow identification of novel submicroscopic DNA copy number alterations (aCNAs) and copy-neutral loss of heterozygosity (cnLOH) resulting in homozygosity for known gene mutations in myeloid neoplasms. We describe the use of an oligo-SNP array for genomic profiling of aCNA and cnLOH, together with sequence analysis of recurrently mutated genes, in a patient with myelodysplastic syndrome (MDS) presenting with normal karyotype and FISH results. Oligo-SNP array analysis revealed a hemizygous deletion of 896 kb at chromosome 5q31.2, representing the smallest 5q deletion reported to date. The deletion involved multiple genes, including two tumor suppressor candidate genes (CTNNA1 and HSPA9) that are associated with MDS/AML. The SNP-array study also detected 3 segments of somatic cnLOH: one involved the entire long arm of chromosome 4; the second involved the distal half of the long arm of chromosome 7, and the third encompassed the entire chromosome 22 (UPD 22). Sequence analysis revealed mutations in TET2 (4q), EZH2 (7q), ASXL1 (20q11.21), and RUNX1 (21q22.3). Coincidently, TET2 and EZH2 were located at segments of cnLOH resulting in their homozygosity. Loss of heterozygosity affecting these two chromosomes and mutations in TET2 and EZH2 are indicative of a myelodysplastic syndrome with a poor prognosis. Deletion of the tumor suppressor genes CTNNA1 and HSPA9 is also likely to contribute to a poor prognosis. Furthermore, the original cnLOHs in multiple chromosomes and additional cnLOH 14q in the follow-up study suggest genetic evolution of the disease and poor prognosis. This study attests to the fact that some patients with a myelodysplastic syndrome who exhibit a normal karyotype may have underlying genetic abnormalities detectable by chromosomal microarray and/or targeted mutation analyses.

The genetics of the myelodysplastic syndromes: Classical cytogenetics and recent molecular insights

Myelodysplastic syndromes (MDS) are a complex group of clonal hematopoietic disorders with an attendant diverse array of associated genetic changes. Conventional cytogenetics plays a prominent and well-established role in determining the contemporary diagnosis and prognosis of these disorders. More recently, molecular approaches have been useful in further characterizing this group of diseases, albeit in a largely experimental context, with the detection of changes at the single gene level including mutations, amplification and epigenetic phenomena. Nevertheless, we remain largely ignorant of the genetic underpinnings of MDS. Here we briefly review the established role of cytogenetics in MDS, and emphasize recent advances in unraveling the genetics of MDS, with a view towards how such findings might facilitate our ability to understand, diagnose and treat these disorders in a more rational manner.

Mortalin, apoptosis, and neurodegeneration

Mortalin is a highly conserved heat-shock chaperone usually found in multiple subcellular locations. It has several binding partners and has been implicated in various functions ranging from stress response, control of cell proliferation, and inhibition/prevention of apoptosis. The activity of this protein involves different structural and functional mechanisms, and minor alterations in its expression level may lead to serious biological consequences, including neurodegeneration. In this article we review the most current data associated with mortalin's binding partners and how these protein-protein interactions may be implicated in apoptosis and neurodegeneration. A complete understanding of the molecular pathways in which mortalin is involved is important for the development of therapeutic strategies for cancer and neurodegenerative diseases.

Allelic methylation levels of the noncoding VTRNA2-1 located on chromosome 5q31.1 predict outcome in AML

Deletions of chromosome 5q are associated with poor outcomes in acute myeloid leukemia (AML) suggesting the presence of tumor suppressor(s) at the locus. However, definitive identification of putative tumor suppressor genes remains controversial. Here we show that a 106-nucleotide noncoding RNA vault RNA2-1 (vtRNA2-1), previously misannotated as miR886, could potentially play a role in the biology and prognosis of AML. vtRNA2-1 is transcribed by polymerase III and is monoallelically methylated in 75% of healthy individuals whereas the remaining 25% of the population have biallelic hypomethylation. AML patients without methylation of VTRNA2-1 have a considerably better outcome than those with monoallelic or biallelic methylation (n = 101, P = .001). We show that methylation is inversely correlated with vtRNA2-1 expression, and that 5-azanucleosides induce vtRNA2-1 and down-regulate the phosphorylated RNA-dependent protein kinase (pPKR), whose activity has been shown to be modulated by vtRNA2-1. Because pPKR promotes cell survival in AML, the data are consistent with vtRNA2-1 being a tumor suppressor in AML. This is the first study to show that vtRNA2-1 might play a significant role in AML, that it is either mono- or biallelically expressed in the blood cells of healthy individuals, and that its methylation state predicts outcome in AML.

Knockdown of Hspa9, a del(5q31.2) gene, results in a decrease in hematopoietic progenitors in mice

Heterozygous deletions spanning chromosome 5q31.2 occur frequently in the myelodysplastic syndromes (MDS) and are highly associated with progression to acute myeloid leukemia (AML) when p53 is mutated. Mutagenesis screens in zebrafish and mice identified Hspa9 as a del(5q31.2) candidate gene that may contribute to MDS and AML pathogenesis, respectively. To test whether HSPA9 haploinsufficiency recapitulates the features of ineffective hematopoiesis observed in MDS, we knocked down the expression of HSPA9 in primary human hematopoietic cells and in a murine bone marrow-transplantation model using lentivirally mediated gene silencing. Knockdown of HSPA9 in human cells significantly delayed the maturation of erythroid precursors, but not myeloid or megakaryocytic precursors, and suppressed cell growth by 6-fold secondary to an increase in apoptosis and a decrease in the cycling of cells compared with control cells. Erythroid precursors, B lymphocytes, and the bone marrow progenitors c-kit(+)/lineage(-)/Sca-1(+) (KLS) and megakaryocyte/erythrocyte progenitor (MEP) were significantly reduced in a murine Hspa9-knockdown model. These abnormalities suggest that cooperating gene mutations are necessary for del(5q31.2) MDS cells to gain clonal dominance in the bone marrow. Our results demonstrate that Hspa9 haploinsufficiency alters the hematopoietic progenitor pool in mice and contributes to abnormal hematopoiesis.

The genetic basis of myelodysplastic syndromes

Myelodysplastic syndrome (MDS) disorders are clonal diseases that often carry stereotypic chromosomal abnormalities. A smaller proportion of cases harbor point mutations that activate oncogenes or inactivate tumor suppressor genes. New technologies have accelerated the pace of discovery and are responsible for the identification of novel genetic mutations associated with MDS and other myeloid neoplasms. These discoveries have identified novel mechanisms in the pathogenesis of MDS. This article touches on the better known genetic abnormalities in MDS and explains in greater detail those that have been discovered more recently. Understanding how mutations lead to MDS and how they might cooperate with each other has become more complicated as the number of MDS-associated genetic abnormalities has grown. In some cases, these mutations have prognostic significance that could improve upon the various prognostic scoring systems in common clinical use.

Cloning, characterization, and functional studies of a human 40-kDa catecholamine-regulated protein: implications in central nervous system disorders

Catecholamine-regulated proteins (CRPs) have been shown to bind dopamine and other structurally related catecholamines; in particular, the 40-kDa CRP (CRP40) protein has been previously cloned and functionally characterized. To determine putative human homologs, BLAST analysis using the bovine CRP40 sequence identified a human established sequence tag (EST) with significant homology (accession #BQ224193). Using this EST, we cloned a recombinant human brain CRP40-like protein, which possessed chaperone activity. Radiolabeled dopamine binding studies with recombinant human CRP40 protein demonstrated the ability of this protein to bind dopamine with low affinity and high capacity. The full-length human CRP40 nucleotide sequence was elucidated (accession #DQ480334) with RNA ligase-mediated rapid amplification of complementary DNA ends polymerase chain reaction, while Northern blot hybridization suggested that human CRP40 is an alternative splice variant of the 70-kDa mitochondrial heat shock protein, mortalin. Human SH-SY5Y neuroblastoma cells treated with the antipsychotic drug, haloperidol, exhibited a significant increase in CRP40 messenger RNA expression compared to untreated control cells, while other dopamine agonists/antagonists also altered CRP40 expression and immunolocalization. In conclusion, these results show that we have cloned a splice variant of mortalin with a novel catecholamine binding function and that this chaperone-like protein may be neuroprotective in dopamine-related central nervous system disorders.

Integrated genomic analysis implicates haploinsufficiency of multiple chromosome 5q31.2 genes in de novo myelodysplastic syndromes pathogenesis

Deletions spanning chromosome 5q31.2 are among the most common recurring cytogenetic abnormalities detectable in myelodysplastic syndromes (MDS). Prior genomic studies have suggested that haploinsufficiency of multiple 5q31.2 genes may contribute to MDS pathogenesis. However, this hypothesis has never been formally tested. Therefore, we designed this study to systematically and comprehensively evaluate all 28 chromosome 5q31.2 genes and directly test whether haploinsufficiency of a single 5q31.2 gene may result from a heterozygous nucleotide mutation or microdeletion. We selected paired tumor (bone marrow) and germline (skin) DNA samples from 46 de novo MDS patients (37 without a cytogenetic 5q31.2 deletion) and performed total exonic gene resequencing (479 amplicons) and array comparative genomic hybridization (CGH). We found no somatic nucleotide changes in the 46 MDS samples, and no cytogenetically silent 5q31.2 deletions in 20/20 samples analyzed by array CGH. Twelve novel single nucleotide polymorphisms were discovered. The mRNA levels of 7 genes in the commonly deleted interval were reduced by 50% in CD34+ cells from del(5q) MDS samples, and no gene showed complete loss of expression. Taken together, these data show that small deletions and/or point mutations in individual 5q31.2 genes are not common events in MDS, and implicate haploinsufficiency of multiple genes as the relevant genetic consequence of this common deletion.

RIL, a LIM Gene on 5q31, Is Silenced by Methylation in Cancer and Sensitizes Cancer Cells to Apoptosis

Gene silencing associated with promoter methylation can inactivate tumor suppressor genes (TSG) in cancer. We identified RIL, a LIM domain gene mapping to 5q31, a region frequently deleted in acute myelogenous leukemia (AML) and myelodysplastic syndrome (MDS), as methylated in 55 of 79 (70%) of cancer cell lines tested. In a variety of primary tumors, we found RIL methylation in 55 of 92 (60%) cases, with highest methylation in AML and colon cancer, and in 30 of 83 (36%) MDS samples, whereas normal tissues showed either absence or substantially lower levels of methylation, which correlates with age. RIL is ubiquitously expressed but silenced in methylated cancers and could be reactivated by the hypomethylating agent 5-aza-2'-deoxycytidine. Restoring RIL expression in colon cancer cells by stable transfection resulted in reduced cell growth and clonogenicity and an approximately 2.0-fold increase in apoptosis following UV exposure. In MDS, RIL methylation is a marker of adverse prognosis independent of chromosome 5 and 7 deletions. Our data suggest that RIL is a good candidate TSG silenced by hypermethylation in cancer.

Three faces of mortalin: a housekeeper, guardian and killer

Mortalin was first cloned as a mortality factor that existed in the cytoplasmic fractions of normal, but not in immortal, mouse fibroblasts. A decade of efforts have expanded its persona from a house keeper protein involved in mitochondrial import, energy generation and chaperoning of misfolded proteins, to a guardian of stress that has multiple binding partners and to a killer protein that contributes to carcinogenesis on one hand and to old age disorders on the other. Being proved to be an attractive target for cancer therapy, it also warrants attention from the perspectives of management of old age diseases and healthy aging.

Chromosome 5 imbalance mapping in breast tumors from BRCA1 and BRCA2 mutation carriers and sporadic breast tumors

Comparative genomic hybridization (CGH) analysis has shown that chromosome 5q deletions are the most frequent aberration in breast tumors from BRCA1 mutation carriers. To map the location of putative 5q tumor suppressor gene(s), 26 microsatellite markers covering chromosome 5 were used in loss of heterozygosity (LOH) analysis of breast tumors from BRCA1 (n = 42) and BRCA2 mutation carriers (n = 67), as well as in sporadic cases (n = 65). High-density array CGH was also used to map chromosome 5 imbalance in 10 BRCA1 tumors. A high LOH frequency was found in BRCA1 tumors (range 19-82%), as compared to BRCA2 and sporadic tumors (ranges 11-44% and 7-43%, respectively). In all, 11 distinct chromosome 5 regions with LOH were observed, the most frequent being 5q35.3 (82%), 5q14.2 (71%) and 5q33.1 (69%) in BRCA1 tumors; 5q35.3 (44%), 5q31.3 (43%) and 5q13.3 (43%) in BRCA2 tumors and 5q31.3 (43%) in sporadic tumors. Array CGH analysis confirmed the very high frequency of 5q deletions, including candidate tumor suppressor genes such as XRCC4, RAD50, RASA1, APC and PPP2R2B. In addition, 2 distinct homozygous deletions were identified, spanning regions of 0.7-1.5 Mbp on 5q12.1 and 5q12.3-q13.1, respectively. These regions include only a few genes, most notably BRCC3/DEPDC1B (pleckstrin/G protein interacting and RhoGAP domains) and PIK3R1 (PI3 kinase P85 regulatory subunit). Significant association (p < or = 0.05) was found between LOH at certain 5q regions and factors of poor prognosis, including negative estrogen and progesterone receptor status, high grade, large tumor size and high portion of cells in S-phase. In conclusion, our results confirm a very high prevalence of chromosome 5q alterations in BRCA1 tumors, pinpointing new regions and genes that should be further investigated.

Proteomic analysis of the Gallus gallus embryo at stage-29 of development

The chicken (Gallus gallus) is one of the primary models for embryological and developmental studies. In order to begin to understand the molecular mechanisms underlying the normal and abnormal development of the chicken, we used 2-DE to construct a whole-embryo proteome map. Proteins were separated by IEF on IPG strips, and by 11% SDS-PAGE) gels. Protein identification was performed by means of PMF with MALDI-TOF-MS. In all, 105 protein spots were identified, 35 of them implicated in embryo development, 10 related with some diseases, and 16, finally, being proteins that have never been identified, purified or characterized in the chicken before. This map will be updated continuously and will serve as a reference database for investigators, studying changes at the protein level under different physiological conditions.

Loss of Hspa9b in zebrafish recapitulates the ineffective hematopoiesis of the myelodysplastic syndrome

Myelodysplastic syndrome (MDS) comprises a heterogeneous group of often fatal hematopoietic stem cell disorders for which neither curative nor standard treatment exists. The complex karyotypes and multistep nature of MDS have severely restricted the identification of causative genetic mutations and thus limited insight into new and more effective therapies. Here we describe a zebrafish mutant crimsonless (crs) with a developmental blood defect that closely recapitulates the ineffective hematopoiesis of MDS including anemia, dysplasia, increased blood cell apoptosis, and multilineage cytopenia. By positional cloning, rescue, and morpholino knockdown experiments, we demonstrate that crs encodes a conserved mitochondrial matrix chaperone HSPA9B containing a glycine-to-glutamate substitution within the substrate-binding domain. This mutation compromises mitochondrial function, producing oxidative stress and apoptosis distinctly in blood cells. Thus, we identify an essential role for Hspa9b in hematopoiesis and implicate both loss of HSPA9B specifically and mitochondrial dysfunction generally in the pathogenesis of the MDS.

Changes in the proteome associated with the action of Bcr-Abl tyrosine kinase are not related to transcriptional regulation

Chronic myeloid leukemia (CML) is a hematopoietic stem cell disease, the hallmark of which is the Bcr-Abl protein tyrosine kinase (PTK). Without intervention the disease progresses from a benign chronic phase to a rapidly fatal blast crisis. To identify the molecular mechanisms underlying disease progression we used two-dimensional gel electrophoresis on a model we have previously described using the expression of a conditional mutant of Bcr-Abl PTK in a multipotent stem cell line, FDCP-Mix. Long term exposure of FDCP-Mix cells to Bcr-Abl mimics disease progression in CML. Four major differences were observed as a consequence of long term exposure to the Bcr-Abl PTK compared with cells exposed short term. The proteins were identified using matrix-assisted laser desorption ionization-time of flight mass spectrometry-generated peptide mass fingerprint data and liquid chromatography-tandem mass spectrometry-generated sequence information. Leukotriene A4 hydrolase, an enzyme known to be deregulated in CML, was found to be up-regulated. Annexin VI, vacuolar ATP synthase catalytic subunit A, and mortalin were found to be down-regulated. Poly(A) PCR cDNA analysis showed there was no correlation between the protein expression changes and mRNA levels. Western blot analysis also indicated no change in the levels of mortalin or leukotriene A4 hydrolase, indicating that post-translational events may modify protein content of the specific spots. Leukotriene B4 levels (product of leukotriene A4 hydrolase) were, however, reduced in cells exposed long term to Bcr-Abl activity. This study demonstrates the potential of proteomic analysis to define novel effects of oncogenes.

A novel nuclear protein, 5qNCA (LOC51780) is a candidate for the myeloid leukemia tumor suppressor gene on chromosome 5 band q31

Interstitial deletion or loss of chromosome 5, del(5q) or -5, is a frequent finding in myeloid leukemias and myelodysplasias, suggesting the presence of a tumor suppressor gene within the deleted region. In our search for this gene, we identified a candidate, 5qNCA (LOC51780), which lies within a consistently-deleted segment of 5q31. 5qNCA expresses a 7.2-kb transcript with a 5286-bp open reading frame which is present at high levels in heart, skeletal muscle, kidney, placenta, and liver as well as CD34+ cells and AML cell lines. 5qNCA encodes a 191-kD nuclear protein which contains a highly-conserved C-terminus containing a zinc finger with the unique spacing Cys-X2-Cys-X7-His-X2-Cys-X2-Cys-X4-Cys-X2-Cys and a jmjC domain, which is often found in proteins that regulate chromatin remodeling. Expression of 5qNCA in a del(5q) cell line results in suppression of clonogenic growth. Preliminary sequence results in AML and MDS samples and cell lines has revealed a possible mutation in the KG-1 cell line resulting in a THR to ALA substitution that has not been found in over 100 normal alleles to date. We propose 5qNCA is a good candidate for the del(5q) tumor suppressor gene based on its predicted function and growth suppressive activities, and suggest that further mutational and functional study of this interesting gene is warranted.

Chromosome and molecular abnormalities in myelodysplastic syndromes

Cytogenetic abnormalities are seen in approximately 50% of cases of myelodysplastic syndrome (MDS) and 80% of cases of secondary MDS (following chemotherapy or radiotherapy). These abnormalities generally consist of partial or complete chromosome deletion or addition (del5q, -7, +8, -Y, del20q), whereas balanced or unbalanced translocations are rarely found in MDS. Fluorescence hybridization techniques (fluorescence in situ hybridization [FISH], multiplex FISH, and spectral karyotyping) are useful in detecting chromosomal anomalies in cases in which few mitoses are obtained or rearrangements are complex. Ras mutations are the molecular abnormalities most frequently found in MDS, followed by p15 gene hypermethylation, FLT3 duplications, and p53 mutations, but none of these abnormalities are specific for MDS. The rare cases of balanced translocations in MDS have allowed the identification of genes whose rearrangements appear to play a role in the pathogenesis of some cases of MDS. These genes include MDS1-EVI1 in t(3;3) or t(3;21) translocations, TEL in t(5;12), HIP1 in t(5;7), MLF1 in t(3;5), and MEL1 in t(1;3). Genes more frequently implicated in the pathogenesis of MDS cases, such as those involving del5q, remain unknown, although some candidate genes are currently being studied. Cytogenetic and known molecular abnormalities generally carry a poor prognosis in MDS and can be incorporated into prognostic scoring systems such as the International Prognostic Scoring System.