The small population of PIG-A mutant cells in myelodysplastic syndromes do not arise from multipotent hematopoietic stem cells

Applications of Flow Cytometry in Diagnosis and Evaluation of Red Blood Cell Disorders

Clinical flow cytometry plays a vital role in the diagnosis and monitoring of various red blood cell disorders. The high throughput, precision, and automation potential of this technique allows for cost-effective and timely analysis compared to older and more manual test methods. Flow cytometric analysis serves as the gold standard diagnostic method for multiple hematological disorders, especially in clinical scenarios where an assay needs to have high sensitivity, high specificity, and a short turnaround time. In this review, we discuss the role of flow cytometric analysis in paroxysmal nocturnal hemoglobinuria, fetal-maternal hemorrhage, and hereditary spherocytosis.

The spectrum of paroxysmal nocturnal hemoglobinuria clinical presentation in a Brazilian single referral center

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare hematological disorder caused by the expansion of a hematopoietic clone harboring a somatic genetic variant in the PIG-A gene translating into a wide spectrum of clinical and laboratory changes, from intravascular hemolysis, thrombosis, and bone marrow failure to subclinical presentation. In this study, we retrospectively analyzed 87 consecutive cases (39 women; median follow-up, 18 months; range, 0–151 months) in whom a PNH clone was detected by flow cytometry between 2006 and 2019 seen at a single Brazilian referral center. The median age at diagnosis was 29 years (range, 8 to 83 years); 29 patients (33%) were initially classified as PNH/bone marrow failure, 13 (15%) as classic PNH, and 45 (52%) as subclinical PNH. The median overall survival (OS) of the entire cohort was not reached during follow-up, without significant differences between groups. At diagnosis, the median PNH clone size was 2.8% (range, 0 to 65%) in erythrocytes and 5.4% (range, 0 to 80%) in neutrophils. Fourteen patients experienced clone expansion during follow-up; in other 14 patients the clone disappeared, and in 18 patients it remained stable throughout the follow-up. A subclinical PNH clone was detected in three telomeropathy patients at diagnosis, but it was persistent and confirmed by DNA sequencing in only one case. In conclusion, PNH presentation was variable, and most patients had subclinical disease or associated with marrow failure and did not require specific anticomplement therapy. Clone size was stable or even disappeared in most cases.

Paroxysmal nocturnal hemoglobinuria and myelodysplastic syndrome: Disappearance of cytogenetic abnormalities

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare life-threatening disease resulting from clonal hematopoietic stem cell evolution. There is a strong link between PNH and other acquired bone marrow failure syndromes, including myelodysplastic syndrome (MDS). Cytogenetic, morphological abnormalities or both are observed in the range of MDS/PNH diagnosis. Herein, we investigate cytogenetic abnormalities in PNH patients. We found two patients with PNH clones and MDS-associated abnormalities that later disappeared. The first patient, originally diagnosed with MDS and Trisomy 6, developed a large PNH clone. At the time of PNH diagnosis, the abnormal cytogenetic clone was no longer detectable despite persistent trilineage dysplasia. In the second patient, a large PNH clone and MDS-defining abnormality were detected at diagnosis, without evidence of dysplasia. No cytogenetic abnormalities were evident after complement inhibition. Our report adds significant information on the complex link between MDS and PNH, suggesting that distinction between these entities may be difficult in some cases. Especially in transplant eligible patients, the clinical phenotype may be the leading feature for treatment decisions in the era of complement inhibition. Lastly, the transient presence of cytogenetic abnormalities is a unique characteristic of our patients' course that needs to be further elucidated in larger studies.

Dietary and lifestyle factors effect erythrocyte PIG-A mutant frequency in humans

It is well understood that poor diet and lifestyle choices can increase the risk of cancer. It is also well documented that cancer is a disease of DNA mutations, with mutations in key genes driving carcinogenesis. Measuring these mutations in a minimally invasive way may be informative as to which exposures are harmful and thus allow us to introduce primary preventative measures, in a bid to reduce cancer incidences. Here, we have measured mutations in the phosphatidylinositol glycan class A (PIG-A) gene in erythrocytes from healthy volunteers (n = 156) and from non-cancer patients attending the local endoscopy department (n = 144). The X-linked PIG-A gene encodes an enzyme involved in glycosylphosphatidylinositol (GPI) anchor synthesis. A silencing mutation in which leads to the absence of GPI anchors on the extracellular surface which can be rapidly assessed using flow cytometry. The background level of PIG-A mutant erythrocytes was 2.95 (95% CI: 2.59-3.67) mutant cells (10-6). Older age increased mutant cell frequency (P < 0.001). There was no difference in mutant cell levels between males and females (P = 0.463) or smokers and non-smokers (P = 0.186). In the endoscopy group, aspirin users had lower mutant frequencies (P = 0.001). Further information on diet and exercise was available for the endoscopy patient group alone, where those with a higher health promotion index score had lower mutant frequencies (P = 0.011). Higher dietary intake of vegetables reduced mutant cell levels (P = 0.022). Participants who exercised for at least 1 h a week appeared to have reduced mutant frequencies than those who did not exercise, although this was not statistically significant (P = 0.099). This low background level of mutant erythrocytes in a population makes this assay an attractive tool to monitor exposures such as those associated with lifestyles and diet, as demonstrated here.

Clonal Cell Proliferation in Paroxysmal Nocturnal Hemoglobinuria: Evaluation of PIGA Mutations and T-cell Receptor Clonality

Background

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired pluripotent hematopoietic stem cell disorder associated with an increase in the number of glycosyl-phosphatidyl inositol (GPI)-deficient blood cells. We investigated PNH clonal proliferation in the three cell lineages—granulocytes, T lymphocytes, and red blood cells (RBCs)—by analyzing PIGA gene mutations and T-cell receptor (TCR) clonality.

Methods

Flow cytometry was used on peripheral blood samples from 24 PNH patients to measure the GPI-anchored protein (GPI-AP) deficient fraction in each blood cell lineage. PIGA gene mutations were analyzed in granulocytes and T lymphocytes by Sanger sequencing. A TCR clonality assay was performed in isolated GPI-AP deficient T lymphocytes.

Results

The GPI-AP deficient fraction among the three lineages was the highest in granulocytes, followed by RBCs and T lymphocytes. PIGA mutations were detected in both granulocytes and T lymphocytes of 19 patients (79.2%), with a higher mutation burden in granulocytes. The GPI-AP deficient fractions of granulocytes and T lymphocytes correlated moderately (r_s=0.519, P=0.049) and strongly (r_s=0.696, P=0.006) with PIGA mutation burden, respectively. PIGA mutations were more frequently observed in patients with clonal rearrangements in TCR genes (P=0.015). The PIGA mutation burden of T lymphocytes was higher in patients with clonal TCRB rearrangement.

Conclusions

PIGA mutations were present in approximately 80% of PNH patients. PNH clone size varies according to blood cell lineage, and clonal cells may obtain proliferation potential or gain a survival advantage over normal cells.

ICCS/ESCCA consensus guidelines to detect GPI-deficient cells in paroxysmal nocturnal hemoglobinuria (PNH) and related disorders part 1 - clinical utility

Paroxysmal nocturnal hemoglobinuria (PNH) arises as a consequence of the non-malignant clonal expansion of one or more hematopoietic stem cells with an acquired somatic mutation of the PIGA gene (Brodsky RA. Blood 113 (2009) 6522-6527). Progeny of affected stem cells are deficient in glycosyl phosphatidylinositol-anchored proteins (GPI-APs). This deficiency is readily detected by flow cytometry. Though this seems straightforward, the clinical utility of this testing requires that the ordering clinician understand not only the characteristics of the test, but also the biology of the underlying disease, and the clinical and laboratory manifestations in the individual patient. When interpreted correctly, the results from PNH flow cytometry testing, including presence and size of the clonal populations and the cell types involved, can allow the clinician to classify the disease appropriately; evaluate the risk of disease progression; and subsequently monitor response to therapy. In these guidelines, we discuss the evaluation of a patient with suspected PNH or other bone marrow failure disorders, with specific emphasis on the contribution of this testing to the diagnosis, classification, and monitoring of patients. For convenience we will commonly refer to these flow cytometry studies as "PNH testing" recognizing that an abnormal result is not diagnostic of PNH; rather both laboratory and clinical features are used to establish this diagnosis. © 2017 International Clinical Cytometry Society.

Paroxysmal nocturnal hemoglobinuria testing in patients with myelodysplastic syndrome in clinical practice-frequency and indications

Background

Myelodysplastic syndrome (mds) is characterized by peripheral blood cytopenias, with most patients developing significant anemia and dependence on red blood cell (rbc) transfusion. In paroxysmal nocturnal hemoglobinuria (pnh), mutations in the PIGA gene lead to lack of cell-surface glycosylphosphatidylinositol, allowing complement-mediated lysis to occur. Paroxysmal nocturnal hemoglobinuria results in direct antiglobulin test-negative hemolysis and cytopenias, and up to 50% of patients with mds test positive for pnh cells. We wanted to determine whether pnh is considered to be a contributor to anemia in mds.

Methods

Patients with a diagnosis of mds confirmed by bone-marrow biopsy since 2009 were reviewed. High-resolution pnh testing by flow cytometry examined flaer (fluorescein-labeled proaerolysin) binding and expression of CD14, CD15, CD24, CD45, CD59, CD64, and CD235 on neutrophils, monocytes, and rbcs.

Results

In 152 patients with mds diagnosed in 2009 or later, the mds diagnosis included subtypes associated with pnh positivity (refractory anemia, n = 7, and hypoplastic mds, n = 4). Of 11 patients who underwent pnh testing, 1 was positive (9.0%). Reasons for pnh testing were anemia (n = 3), new mds diagnosis (n = 2), hypoplastic mds (n = 2), decreased haptoglobin (n= 1), increased rbc transfusion requirement (n= 1), and unexplained iron deficiency (n= 1).

Conclusions

Testing for pnh was infrequent in mds patients, and the criteria for testing were heterogeneous. Clinical indicators prompted pnh testing in 6 of 11 patients. Given that effective treatment is now available for pnh and that patients with pnh-positive mds can respond to immunosuppressive therapy, pnh testing in mds should be considered. Prospective analyses to clarify the clinical significance of pnh positivity in mds are warranted.

PIGN gene expression aberration is associated with genomic instability and leukemic progression in acute myeloid leukemia with myelodysplastic features

Previous studies have linked increased frequency of glycosylphosphatidylinositol-anchor protein (GPI-AP) deficiency with genomic instability and the risk of carcinogenesis. However, the underlying mechanism is still not clear. A randomForest analysis of the gene expression array data from 55 MDS patients (GSE4619) demonstrated a significant (p = 0.0007) correlation (Pearson r =-0.4068) between GPI-anchor biosynthesis gene expression and genomic instability, in which PIGN, a gene participating in GPI-AP biosynthesis, was ranked as the third most important in predicting risk of MDS progression. Furthermore, we observed that PIGN gene expression aberrations (increased transcriptional activity but diminished to no protein production) were associated with increased frequency of GPI-AP deficiency in leukemic cells during leukemic transformation/progression. PIGN gene expression aberrations were attributed to partial intron retentions between exons 14 and 15 resulting in frameshifts and premature termination which were confirmed by examining the RNA-seq data from a group of AML patients (phs001027.v1.p1). PIGN gene expression aberration correlated with the elevation of genomic instability marker expression that was independent of the TP53 regulatory pathway. Suppression/elimination of PIGN protein expression caused a similar pattern of genomic instability that was rescued by PIGN restoration. Finally, we found that PIGN bound to the spindle assembly checkpoint protein, MAD1, and regulated its expression during the cell cycle. In conclusion, PIGN gene is crucial in regulating mitotic integrity to maintain chromosomal stability and prevents leukemic transformation/progression.

Paroxysmal nocturnal haemoglobinuria

Paroxysmal nocturnal haemoglobinuria (PNH) is a clonal haematopoietic stem cell (HSC) disease that presents with haemolytic anaemia, thrombosis and smooth muscle dystonias, as well as bone marrow failure in some cases. PNH is caused by somatic mutations in PIGA (which encodes phosphatidylinositol N-acetylglucosaminyltransferase subunit A) in one or more HSC clones. The gene product of PIGA is required for the biosynthesis of glycosylphosphatidylinositol (GPI) anchors; thus, PIGA mutations lead to a deficiency of GPI-anchored proteins, such as complement decay-accelerating factor (also known as CD55) and CD59 glycoprotein (CD59), which are both complement inhibitors. Clinical manifestations of PNH occur when a HSC clone carrying somatic PIGA mutations acquires a growth advantage and differentiates, generating mature blood cells that are deficient of GPI-anchored proteins. The loss of CD55 and CD59 renders PNH erythrocytes susceptible to intravascular haemolysis, which can lead to thrombosis and to much of the morbidity and mortality of PNH. The accumulation of anaphylatoxins (such as C5a) from complement activation might also have a role. The natural history of PNH is highly variable, ranging from quiescent to life-threatening. Therapeutic strategies include terminal complement blockade and bone marrow transplantation. Eculizumab, a monoclonal antibody complement inhibitor, is highly effective and the only licensed therapy for PNH.

Paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare bone marrow failure disorder that manifests with hemolytic anemia, thrombosis, and peripheral blood cytopenias. The absence of two glycosylphosphatidylinositol (GPI)-anchored proteins, CD55 and CD59, leads to uncontrolled complement activation that accounts for hemolysis and other PNH manifestations. GPI anchor protein deficiency is almost always due to somatic mutations in phosphatidylinositol glycan class A (PIGA), a gene involved in the first step of GPI anchor biosynthesis; however, alternative mutations that cause PNH have recently been discovered. In addition, hypomorphic germ-line PIGA mutations that do not cause PNH have been shown to be responsible for a condition known as multiple congenital anomalies-hypotonia-seizures syndrome 2. Eculizumab, a first-in-class monoclonal antibody that inhibits terminal complement, is the treatment of choice for patients with severe manifestations of PNH. Bone marrow transplantation remains the only cure for PNH but should be reserved for patients with suboptimal response to eculizumab.

The challenging world of cytopenias: distinguishing myelodysplastic syndromes from other disorders of marrow failure

Over the past decade, our understanding of bone marrow failure has advanced considerably. Marrow failure encompasses multiple overlapping diseases, and there is increasing availability of diagnostic tools to distinguish among the subtypes. Identification of genetic alterations that underlie marrow failure has also greatly expanded, especially for myelodysplastic syndromes. Molecular markers are increasingly used to guide the management of myelodysplasia and may distinguish this diagnosis from other marrow failure disorders. This review summarizes the current state of distinguishing among causes of marrow failure and discusses the potential uses of multiple diagnostic and prognostic indicators in the management of myelodysplastic syndromes and other bone marrow failure disorders.

Paroxysmal nocturnal hemoglobinuria and the age of therapeutic complement inhibition

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare disease of hematopoietic stem cells due to a mutation in the PIG-A gene leading to a deficiency of GPI-anchored proteins. Lack of two specific GPI-anchored proteins, CD55 and CD59, leads to uncontrolled complement activation that result in both intravascular and extravascular hemolysis. Free hemoglobin leads to nitric oxide depletion that mediates the pathophysiology of some of the common clinical signs of PNH. Clinical symptoms of PNH include evidence of hemolytic anemia, bone marrow failure, smooth muscle dystonias and thromboses. Treatment options for patients with PNH include bone marrow transplantation, a therapy associated with high morbidity and mortality, or treatment with the complement inhibitor eculizumab. Eculizumab is a first-in-class anti-complement drug that in PNH has been shown to block complement-mediated hemolysis, reduce transfusion dependency, reduce thromboembolic complications and improve the quality of life (QoL) of patients.

Burst-forming unit-erythroid assays to distinguish cellular bone marrow failure disorders

Patients with cytopenias and a cellular bone marrow can be a diagnostic and therapeutic challenge. Previous reports suggested a role for progenitor assays for diagnosis and predicting response to therapy. We report the results of Burst-forming unit-erythroid (BFU-E) assays in 48 consultative cases of single or multilineage cytopenias with cellular marrows. The final diagnoses included 17 patients with myelodysplastic syndrome, 9 patients with pure red cell aplasia (non-large granular lymphocytosis [LGL] in etiology], 15 patients with LGL (eight of whom had a single-lineage cytopenia only, whereas the other seven had multilineage cytopenias), and 7 patients with cytopenias associated with systemic inflammation from autoimmune conditions. In this cohort, nonmalignant diseases were well-distinguished from myelodysplastic syndrome by BFU-E growth. Our data suggest that low BFU-E growth (less than 10 BFU-E per 10(5) marrow mononuclear cells) helps to exclude LGL, pure red cell aplasia, or cytopenias associated with systemic inflammation as a cause of pancytopenia with a sensitivity of 96.8%, specificity of 76.5%, and a predictive value of 88.2% (p = 0.0001). BFU-E growth also was examined to predict treatment response. Of the 29 patients in this cohort treated with immunosuppressive therapy, there was an 86% response rate with 25 responders (11 partial responses and 14 complete responses) and 4 nonresponders. This result correlated with higher BFU-E growth. Our results suggest that BFU-E assays are a useful adjunct in the diagnosis and management of cytopenias in the setting of a normocellular or hypercellular marrows.

Last marrow standing: bone marrow transplantation for acquired bone marrow failure conditions

Paroxysmal nocturnal hemoglobinuria, aplastic anemia, and myelodysplastic syndrome are a spectrum of acquired marrow failure, having a common pathologic thread of both immune dysregulation and the development of abnormal hematopoiesis. Allogeneic hematopoietic cell transplantation plays a critical role in the treatment of these disorders and, for many patients, is the only treatment modality with demonstrated curative potential. In recent years, there have been many breakthroughs in the understanding of the pathogenesis of these uncommon disorders. The subsequent advances in non-transplant therapies, along with concurrent improvement in outcomes after hematopoietic cell transplantation, necessitate continual appraisal of the indications, timing, and approaches to transplantation for acquired marrow failure syndromes. We review here contemporary and critical new findings driving current treatment decisions.