Identification of circular RNAs as novel biomarkers and potentially functional competing endogenous RNA network for myelodysplastic syndrome patients.

Circular RNAs (circRNAs) have been identified to exert vital biological functions and can be used as new biomarkers in a number of tumors. However, little is known about the functions of circRNAs in myelodysplastic syndrome (MDS). Here, we aimed to investigate circRNA expression profiles and to investigate the functional and clinical value of circRNAs in MDS. Differential expression of circRNAs between MDS and control subjects was analyzed using circRNA arrays, in which we identified 145 upregulated circRNAs and 224 downregulated circRNAs. Validated by real-time quantitative PCR between 100 MDS patients and 20 controls, three upregulated (hsa_circRNA_100352, hsa_circRNA_104056, and hsa_circRNA_104634) and three downregulated (hsa_circRNA_103846, hsa_circRNA_102817, and hsa_circRNA_102526) circRNAs matched the arrays. The receiver operating characteristic curve analysis of these circRNAs showed that the area under the curve was 0.7266, 0.8676, 0.7349, 0.7091, 0.8806, and 0.7472, respectively. Kaplan-Meier survival analysis showed that only hsa_circRNA_100352, hsa_circRNA_104056, and hsa_circRNA_102817 were significantly associated with overall survival. Furthermore, we generated a competing endogenous RNA network focused on hsa_circRNA_100352, hsa_circRNA_104056, and hsa_circRNA_102817. Analyses using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes showed that the three circRNAs were linked with some important cancer-related functions and pathways.

Splicing factor mutations in MDS RARS and MDS/MPN-RS-T.

Spliceosomal mutations, especially mutations in SF3B1, are frequently (>80%) identified in patients with refractory anemia with ringed sideroblasts (RARS) and myelodysplastic/myeloproliferative neoplasms with ringed sideroblasts and thrombocytosis (MDS/MPN-RS-T; previously known as RARS-T), and SF3B1 mutations have a high positive predictive value for disease phenotype with ringed sideroblasts. These observations suggest that SF3B1 mutations play important roles in the pathogenesis of these disorders and formation of ringed sideroblasts. Here we will review recent insights into the molecular mechanisms of mis-splicing caused by mutant SF3B1 and the pathogenesis of RSs in the context of congenital sideroblastic anemia as well as RARS with SF3B1 mutations. We will also discuss therapy of SF3B1 mutant MDS, including novel approaches.

"Irony" of managing refractory anemia with transfusional support in hemophagocytic lymphohistiocytosis.

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening derangement of the immune system in which host macrophages phagocytose the patient's own blood cells. Herein, we present the case of a patient with HLH and associated refractory anemia who developed rapid iron deposition in the liver after transfusion of sixteen units of packed red blood cells (RBCs). Before transfusion, neither a liver biopsy nor computed tomography scan demonstrated iron deposition in the organ parenchyma. After receiving sixteen units of packed RBCs, liver iron concentration rose to 6.7 mg/g dry weight, which is highly unusual in other diseases requiring transfusional support.

Diagnosis and treatment of sideroblastic anemias: from defective heme synthesis to abnormal RNA splicing.

The sideroblastic anemias are a heterogeneous group of inherited and acquired disorders characterized by the presence of ring sideroblasts in the bone marrow. X-linked sideroblastic anemia (XLSA) is caused by germline mutations in ALAS2. Hemizygous males have a hypochromic microcytic anemia, which is generally mild to moderate and is caused by defective heme synthesis and ineffective erythropoiesis. XLSA is a typical iron-loading anemia; although most patients are responsive to pyridoxine, treatment of iron overload is also important in the management of these patients. Autosomal recessive sideroblastic anemia attributable to mutations in SLC25A38, a member of the mitochondrial carrier family, is a severe disease: patients present in infancy with microcytic anemia, which soon becomes transfusion dependent. Conservative therapy includes regular red cell transfusion and iron chelation, whereas allogenic stem cell transplantation represents the only curative treatment. Refractory anemia with ring sideroblasts (RARS) is a myelodysplastic syndrome characterized mainly by anemia attributable to ineffective erythropoiesis. The clinical course of RARS is generally indolent, but there is a tendency to worsening of anemia over time, so that most patients become transfusion dependent in the long run. More than 90% of these patients carry somatic mutations in SF3B1, a gene encoding a core component of the RNA splicing machinery. These mutations cause misrecognition of 3' splice sites in downstream genes, resulting in truncated gene products and/or decreased expression attributable to nonsense-mediated RNA decay; this explains the multifactorial pathogenesis of RARS. Variants of RARS include refractory cytopenia with multilineage dysplasia and ring sideroblasts, and RARS associated with marked thrombocytosis; these variants involve additional genetic lesions. Inhibitors of molecules of the transforming growth factor-ß superfamily have been shown recently to target ineffective erythropoiesis and ameliorate anemia both in animal models of myelodysplastic syndrome and in RARS patients.

Alteration in endoglin-related angiogenesis in refractory cytopenia with multilineage dysplasia.

The functional mechanisms involved in angiogenesis and the potential role of endoglin (ENG), recently described as a new marker for this process, have not been explored in Myelodysplastic Syndromes (MDS). In order to gain insight in MDS angiogenesis a combined analysis in bone marrow (BM) of gene expression levels, angiogenesis-related soluble factors and functional angiogenesis-related studies was carried out. Ninety-seven MDS patients and forty-two normal BM samples were studied. The morphology of the capillary-like structures originated by two endothelial cells lines in the BM environment of patients with refractory cytopenia with multilineage dysplasia (RCMD) was different from those of the remaining MDS. In addition, the BM mononuclear cells from RCMD patients displayed over-expression of VEGF, HIF and FN1 while they showed reduced expression of ENG in contrast to the normal ENG expression of the remaining low-risk MDS and the high expression of ENG in high-risk MDS subtype. Moreover, higher soluble ENG and soluble FLT-1 levels in BM microenvironment were observed in RCMD cases, which distinguished them from other individuals. Therefore, the present study suggests that the patterns of angiogenesis are different between the MDS subtypes. The differences in angiogenesis observed in RCMD patients could be related to ENG abnormalities.

Molecular similarity between myelodysplastic form of chronic myelomonocytic leukemia and refractory anemia with ring sideroblasts.

Chronic myelomonocytic leukemia is similar to but a separate entity from both myeloproliferative neoplasms and myelodysplastic syndromes, and shows either myeloproliferative or myelodysplastic features. We ask whether this distinction may have a molecular basis. We established the gene expression profiles of 39 samples of chronic myelomonocytic leukemia (including 12 CD34-positive) and 32 CD34-positive samples of myelodysplastic syndromes by using Affymetrix microarrays, and studied the status of 18 genes by Sanger sequencing and array-comparative genomic hybridization in 53 samples. Analysis of 12 mRNAS from chronic myelomonocytic leukemia established a gene expression signature of 122 probe sets differentially expressed between proliferative and dysplastic cases of chronic myelomonocytic leukemia. As compared to proliferative cases, dysplastic cases over-expressed genes involved in red blood cell biology. When applied to 32 myelodysplastic syndromes, this gene expression signature was able to discriminate refractory anemias with ring sideroblasts from refractory anemias with excess of blasts. By comparing mRNAS from these two forms of myelodysplastic syndromes we derived a second gene expression signature. This signature separated the myelodysplastic and myeloproliferative forms of chronic myelomonocytic leukemias. These results were validated using two independent gene expression data sets. We found that myelodysplastic chronic myelomonocytic leukemias are characterized by mutations in transcription/epigenetic regulators (ASXL1, RUNX1, TET2) and splicing genes (SRSF2) and the absence of mutations in signaling genes. Myelodysplastic chronic myelomonocytic leukemias and refractory anemias with ring sideroblasts share a common expression program suggesting they are part of a continuum, which is not totally explained by their similar but not, however, identical mutation spectrum.

Refractory anemia with ring sideroblasts.

Refractory anemia with ring sideroblasts (RARS) is a subtype of myelodysplastic syndrome (MDS) characterized by 15% or more ring sideroblasts in the bone marrow according to the WHO classification. After Perls staining, ring sideroblasts are defined as erythroblasts in which there are 5 or more siderotic granules covering at least a third of the nuclear circumference. The iron deposited in perinuclear mitochondria of ring sideroblasts is present in the form of mitochondrial ferritin. The molecular basis of MDS with ring sideroblasts has remained unknown until recently. In 2011, whole exome sequencing studies revealed somatic mutations of SF3B1, a gene encoding a core component of RNA splicing machinery, in myelodysplasia with ring sideroblasts. The close relationship between SF3B1 mutation and ring sideroblasts is consistent with a causal relationship, and makes SF3B1 the first gene to be associated with a specific morphological feature in MDS. RARS is mainly characterized by isolated anemia due to ineffective erythropoiesis, and its clinical course is generally benign, although there is a tendency to worsening of anemia in most patients over time. By contrast, refractory cytopenia with multilineage dysplasia and ring sideroblasts (RCMD-RS) is characterized by pancytopenia and dysplasia in two or more myeloid cell lineages. More importantly, patients with RCMD-RS have a higher risk of developing bone marrow failure or progressing to acute myeloid leukemia (AML). Refractory anemia with ring sideroblasts (RARS-T) associated with marked thrombocytosis is a myelodysplastic/myeloproliferative neoplasm associated with both SF3B1 and JAK2 or MPL mutations. RARS-T may develop from an SF3B1 mutated RARS through the acquisition of a JAK2 or MPL mutations in a subclone of hematopoietic cells.

Oxidative stress levels in myelodysplastic syndrome patients: their relationship to serum ferritin and haemoglobin values.

Reactive oxygen species (ROS) and serum ferritin levels are both considered to be important biological factors in the pathogenesis of myelodysplastic syndrome (MDS). This study evaluated the levels of ROS in 40 patients with MDS (19 males and 21 females) using the Free Radical Analytical System, FRAS4, and derivatives of reactive oxygen metabolite kits. The patients' mean age was 67.3 years (range 58 - 86 years). The sera of 34 (85%) patients exhibited higher levels of oxidative stress than the reference range. There was a positive correlation between ROS levels and serum ferritin levels, and a negative correlation between ROS levels and haemoglobin levels. There was a negative relationship between serum haemoglobin and ferritin levels. The results indicated that iron accumulation or severe anaemia could contribute to oxidative stress in MDS patients. Iron chelation and antioxidant therapy may be suitable for the management of MDS.

Loss of ABCB7 gene: pathogenesis of mitochondrial iron accumulation in erythroblasts in refractory anemia with ringed sideroblast with isodicentric (X)(q13).

An isodicentric (X)(q13) (idicXq13) is a rare, acquired chromosomal abnormality originated by deletion of the long arm from Xq13 (Xq13-qter), and is found in female patients with hematological disorders involving increased ringed sideroblasts (RSs), which are characterized by mitochondrial iron accumulation around the erythroblast nucleus. The cause of increased RSs in idicXq13 patients is not fully understood. Here, we report the case of a 66-year-old female presenting with refractory anemia with ringed sideroblasts (RARS), and idicXq13 on G-banded analysis. We identify the loss of the ABCB7 (ATP-binding cassette subfamily B member-7) gene, which is located on Xq13 and is involved in mitochondrial iron transport to the cytosol, by fluorescent in situ hybridization (FISH) analysis and the decreased expression level of ABCB7 mRNA in the patient's bone marrow cells. Further FISH analyses showed that the ABCB7 gene is lost only on the active X-chromosome, not on the inactive one. We suggest that loss of ABCB7 due to deletion of Xq13-qter at idicXq13 formation may have contributed to the increased RSs in this patient. These findings suggest that loss of the ABCB7 gene may be a pathogenetic factor underlying mitochondrial iron accumulation in RARS patients with idicXq13.

Refractory anemia with ring sideroblasts associated with marked thrombocytosis: a mixed group exhibiting a spectrum of morphologic findings.

Refractory anemia with ring sideroblasts associated with marked thrombocytosis (RARS-T) is a provisional entity in the current World Health Organization classification and is thought to be a myelodysplastic/myeloproliferative neoplasm (MDS/MPN). We analyzed 18 cases of RARS-T. All patients had thrombocytosis (platelet count, 515-1,100 × 10(3)/µL [515-1,100 × 10(9)/L]) and anemia (hemoglobin level, 7.2-12.6 g/dL [72-126 g/L]). Three patients had mild leukocytosis (WBC count, 3,900-16,300/µL [3.9-16.3 × 10(9)/L]). Ring sideroblasts were 8% to 75% in the bone marrow. Megakaryocytes showed a spectrum of morphologic findings. JAK2(V617F) was identified in 9 of 15 cases, including 7 of 9 with thrombocytosis (platelet count, >600 × 10(3)/µL [600 × 10(9)/L]) and 1 with 8% ring sideroblasts. The MPL(W515L) mutation was not detected (n = 9). We conclude that RARS-T is a pathogenetically heterogeneous group of limited diagnostic usefulness. Approximately 60% of cases carry JAK2(V617F)and seem to be closer to an MPN in which ring sideroblasts may be a secondary phenomenon. The remaining cases usually lack the JAK2(V617F)mutation, have a platelet count less than 600 × 10(3)/µL (600 × 10(9)/L), and may represent an MDS or MPN with thrombocytosis of unknown mechanisms.

[Clinical and biological features in refractory anemia with ringed sideroblasts with fluctuant platelet counts].

The objective of this study was to explore the differences between refractory anemia with ringed sideroblast (RARS) and RARS associated with marked thrombocytosis (RARS-T) in the clinical, biological features and prognosis. The morphological changes of cells were observed by bone marrow smear and biopsy. Immunologic phenotype was analyzed by flow cytometry, and chromosome was examined by conventional chromosomal analysis. JAK2 V617F and MPL W515L mutations were screened by allele-specific polymerase chain reaction (AS-PCR) and sequence analysis. The results showed that this case was clinically diagnosed as RARS with thrombophilia, the level of serum potassium was positively related with platelet counts. When platelets increased, the clusters of atypical giant platelets and megakaryocytes were observed in peripheral blood and bone marrow examined by bone marrow smear and bone marrow biopsy respectively, JAK2 V617F and MPL W515L mutations were negative. It is concluded that RARS may transform into RARS-T accompanied with megakaryocyte proliferation, large atypical platelets and negative JAK2 V617F. Preventing thrombophilia and monitoring relative gene mutations are necessary when atypical giant platelets and fluctuant platelet counts occurred in process of RARS with tendency to RARS-T.

Erythrocyte membrane defects and asymmetry in paroxysmal nocturnal hemoglobinuria and myelodysplastic syndrome.

Paroxysmal nocturnal hemoglobinuria (PNH) and myelodysplastic syndromes (MDS) are clonal disorder of haematopoietic stem cells that may eventually lead to chronic anemia. The ultrastructural defects in erythrocyte membranes may have a role in early red cell destruction within circulation. The lifespan of the erythrocyte primarily correlates to externalization of phosphatidylserine (PS) and loss of glycophorins from the erythrocyte surface. The span of survival of mature erythrocytes in the circulation in case of MDS and PNH is yet unclear and has been studied by measuring simultaneous exposure of PS and loss of glycoconjugates, primarily glycophorins from membrane surface. The extent of the loss of PS asymmetry and cell surface glycophorins in density separated erythrocytes of six MDS and three PNH patients has been probed by fluorochrome conjugated annexin V and wheat germ agglutinin using flow cytometry. The cells with lighter density showed a higher amount of PS on the outer surface compared to those of heavier cells in all PNH and MDS cases, showing the opposite trend to that observed in normal erythrocytes. In addition, the lighter cells had more cell surface glycophorins compared to heavier cells in all the cases. Such lowering of glycophorin levels from the lighter to heavier cells was maximum in refractory anaemia (RA) and minimum in the normal cells studied. Greater loss of PS asymmetry and cell surface glycophorin in the lighter or younger erythrocytes together could be responsible for their faster destruction and removal (eryptosis) in PNH and MDS.

Gene expression profiling of erythroblasts from refractory anaemia with ring sideroblasts (RARS) and effects of G-CSF.

Refractory anaemia with ring sideroblasts (RARS) is characterized by anaemia, erythroid apoptosis, cytochrome c release and mitochondrial ferritin accumulation. Granulocyte-colony-stimulating factor (G-CSF) inhibits the first three of these features in vitro and in vivo. To dissect the molecular mechanisms underlying the RARS phenotype and anti-apoptotic effects of G-CSF, erythroblasts generated from normal (NBM) and RARS marrow CD34(+) cells were cultured +/-G-CSF and subjected to gene expression analysis (GEP). Several erythropoiesis-associated genes that were deregulated in RARS CD34(+) cells showed normal expression in erythroblasts, underscoring the importance of differentiation-specific GEP. RARS erythroblasts showed a marked deregulation of several pathways including apoptosis, DNA damage repair, mitochondrial function and the JAK/Stat pathway. ABCB7, transporting iron from mitochondria to cytosol and associated with inherited ring sideroblast formation was severely suppressed and expression decreased with differentiation, while increasing in NBM cultures. The same pattern was observed for the mitochondrial integrity gene MFN2. Other downregulated key genes included STAT5B, HSPA5, FANCC and the negative apoptosis regulator MAP3K7. Methylation status of key downregulated genes was normal. The mitochondrial pathway including MFN2 was significantly modified by G-CSF, and several heat shock protein genes were upregulated, as evidence of anti-apoptotic protection of erythropoiesis. By contrast, G-CSF had no effect on iron-transport or erythropoiesis-associated genes.

Spectrum of mutations in RARS-T patients includes TET2 and ASXL1 mutations.

While a majority of patients with refractory anemia with ring sideroblasts and thrombocytosis harbor JAK2V617F and rarely MPLW515L, JAK2/MPL-negative cases constitute a diagnostic problem. 23 RARS-T cases were investigated applying immunohistochemical phospho-STAT5, sequencing and SNP-A-based karyotyping. Based on the association of TET2/ASXL1 mutations with MDS/MPN we studied molecular pattern of these genes. Two patients harbored ASXL1 and another 2 TET2 mutations. Phospho-STAT5 activation was present in one mutated TET2 and ASXL1 case. JAK2V617F/MPLW515L mutations were absent in TET2/ASXL1 mutants, indicating that similar clinical phenotype can be produced by various MPN-associated mutations and that additional unifying lesions may be present in RARS-T.

Accelerated cellular senescence in myelodysplastic syndrome.

OBJECTIVE: To investigate the contribution of cellular senescence to the progression and prognosis of myelodysplastic syndrome (MDS). MATERIALS AND METHODS: We have analyzed the expression of p16INK4a in bone marrow mononuclear cells or CD34(+) cells from 53 patients with MDS, 12 acute myeloid leukemia (AML), and 11 healthy controls. Additionally, We have assessed quantitatively senescence-associated beta-galactosidase (SA-beta-gal) staining on bone marrow mononuclear cells from MDS and AML patients, HL60 and SHI-1 leukemia cell lines, and healthy control cells. RESULTS: An upregulated expression of senescence-associated molecular marker p16INK4a was found in MDS compared with healthy controls, while a lower expression of p16INK4a was observed in AML compared with healthy controls. International Prognostic Scoring System score was negatively correlated with the percentage of p16INK4a-positive cells. The SA-beta-gal activity measured by mean percentage of positive cells was significantly higher in MDS cases when compared with controls. Meanwhile, percentage of SA-beta-gal-positive cells was also remarkably higher in dysplastic cells of MDS when compared to nondysplastic cells from MDS. CONCLUSIONS: These results of our present study suggested an accelerated cellular senescence occurred in MDS, and the cellular senescence may be involved in the progression and prognosis of MDS.

Erythroid precursors from patients with low-risk myelodysplasia demonstrate ultrastructural features of enhanced autophagy of mitochondria.

Recent studies in erythroid cells have shown that autophagy is an important process for the physiological clearance of mitochondria during terminal differentiation. However, autophagy also plays an important role in removing damaged and dysfunctional mitochondria. Defective mitochondria and impaired erythroid maturation are important characteristics of low-risk myelodysplasia. In this study we therefore questioned whether the autophagic clearance of mitochondria might be altered in erythroblasts from patients with refractory anemia (RA, n=3) and RA with ringed sideroblasts (RARS, n=6). Ultrastructurally, abnormal and iron-laden mitochondria were abundant, especially in RARS patients. A large proportion (52+/-16%) of immature and mature myelodysplastic syndrome (MDS) erythroblasts contained cytoplasmic vacuoles, partly double membraned and positive for lysosomal marker LAMP-2 and mitochondrial markers, findings compatible with autophagic removal of dysfunctional mitochondria. In healthy controls only mature erythroblasts comprised these vacuoles (12+/-3%). These findings were confirmed morphometrically showing an increased vacuolar surface in MDS erythroblasts compared to controls (P<0.0001). In summary, these data indicate that MDS erythroblasts show features of enhanced autophagy at an earlier stage of erythroid differentiation than in normal controls. The enhanced autophagy might be a cell protective mechanism to remove defective iron-laden mitochondria.

Growth differentiation factor 15 production is necessary for normal erythroid differentiation and is increased in refractory anaemia with ring-sideroblasts.

The disturbed erythropoiesis in patients with refractory anaemia with ring-sideroblasts (RARS) is characterized by intramedullary apoptosis of erythroid precursors and increased iron accumulation in mitochondria. To gain insight into these pathophysiological mechanisms we compared the gene expression profile (GEP) of erythroid precursors from RARS patients to the GEP of normal erythroid precursors. Three hundred sixty four probe sets were up-, and 253 probe sets downregulated in RARS cells. Interestingly, Growth Differentiation factor 15 (GDF15), a cytokine from the TGFbeta family, was dramatically upregulated in all RARS patients. Measurement of GDF15 in the sera from twenty RARS patients confirmed this finding by showing significantly, 7.2-fold, increased protein levels (3254 +/- 1400 ng/ml vs. 451 +/- 87 ng/ml in normals). In vitro studies demonstrated erythroid-specific production of GDF15 and dependence on erythropoietin. Induction of apoptosis by arsenic trioxide, a drug which acts via reduction of the mitochondrial membrane potential, also stimulated GDF15 production. Downregulation of endogenous GDF15 production in erythoblasts by specific siRNA led to diminished erythroid differentiation. Taken together, our findings demonstrate a new role for GDF15 in normal erythropoiesis as well as in the ineffective erythropoiesis of RARS patients.

Characterization of myelodysplastic syndrome and aplastic anemia by immunostaining of p53 and hemoglobin F and karyotype analysis: differential diagnosis between refractory anemia and aplastic anemia.

P53 mutation has been reported in various solid tumors, acute leukemia and myelodysplastic syndrome (MDS), but the diagnostic significance of p53 in MDS remains to be determined. The purpose of the present paper was to examine p53 mutation and immunostaining of the same patients, because there have been few reports of simultaneous analysis of these markers. Seven p53 mutations were observed among 37 MDS and 11 cases of overt leukemia transformed from MDS (MDS-OL). Mutated p53 mainly observed in high-risk MDS had more intense p53 staining than in MDS with wild-type p53 overexpression. Aplastic anemia (AA) produced no p53 staining. The percentage of p53 staining in MDS (71%) was higher than that of mutated p53 (11%) but did not reach 100% of MDS cases studied, therefore the authors attempted to differentiate MDS, especially refractory anemia (RA) and AA, using a combination of p53 immunostaining, hemoglobin F (HbF) immunostaining and chromosome abnormality, because HbF of erythroblasts was reportedly observed in MDS RA but not in AA. Most MDS/MDS-OL (47/48) had at least one positive marker. Among 11 AA cases, only two were positive for HbF. The present results suggest that the combination of these three markers is useful to discriminate MDS from AA.

The role of the iron transporter ABCB7 in refractory anemia with ring sideroblasts.

Refractory Anemia with Ring Sideroblasts (RARS) is an acquired myelodysplastic syndrome (MDS) characterized by an excess iron accumulation in the mitochondria of erythroblasts. The pathogenesis of RARS and the cause of this unusual pattern of iron deposition remain unknown. We considered that the inherited X-linked sideroblastic anemia with ataxia (XLSA/A) might be informative for the acquired disorder, RARS. XLSA/A is caused by partial inactivating mutations of the ABCB7 ATP-binding cassette transporter gene, which functions to enable transport of iron from the mitochondria to the cytoplasm. Furthermore, ABCB7 gene silencing in HeLa cells causes an accumulation of iron in the mitochondria. We have studied the role of ABCB7 in RARS by DNA sequencing, methylation studies, and gene expression studies in primary CD34(+) cells and in cultured erythroblasts. The DNA sequence of the ABCB7 gene is normal in patients with RARS. We have investigated ABCB7 gene expression levels in the CD34(+) cells of 122 MDS cases, comprising 35 patients with refractory anemia (RA), 33 patients with RARS and 54 patients with RA with excess blasts (RAEB), and in the CD34(+) cells of 16 healthy controls. We found that the expression levels of ABCB7 are significantly lower in the RARS group. RARS is thus characterized by lower levels of ABCB7 gene expression in comparison to other MDS subtypes. Moreover, we find a strong relationship between increasing percentage of bone marrow ring sideroblasts and decreasing ABCB7 gene expression levels. Erythroblast cell cultures confirm the low levels of ABCB7 gene expression levels in RARS. These data provide an important link between inherited and acquired forms of sideroblastic anemia and indicate that ABCB7 is a strong candidate gene for RARS.