Cytogenetic and morphological abnormalities in paroxysmal nocturnal haemoglobinuria

Paroxysmal nocturnal haemoglobinuria (PNH) is characterized by the expansion of a haematopoietic stem cell clone with a PIG-A mutation (the PNH clone) in an environment in which normal stem cells are lost or failing: it has been hypothesized that this abnormal marrow environment provides a relative advantage to the PNH clone. In patients with PNH, generally, the karyotype of bone marrow cells has been reported to be normal, unlike in myelodysplastic syndrome (MDS), another clonal condition in which cytogenetic abnormalities are regarded as diagnostic. In a retrospective review of 46 patients with a PNH clone, we found a karyotypic abnormality in 11 (24%). Upon follow-up, the proportion of cells with abnormal karyotype decreased significantly in seven of these 11 patients. Abnormal morphological bone marrow features reminiscent of MDS were common in PNH, regardless of the karyotype. However, none of our patients developed excess blasts or leukaemia. We conclude that in patients with PNH cytogenetically abnormal clones are not necessarily malignant and may not be predictive of evolution to leukaemia.

Paroxysmal nocturnal hemoglobinuria: insights from recent advances in molecular biology

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare, acquired hemolytic anemia characterized by the increased sensitivity of red cells to complement, leading to intravascular hemolysis and hemoglobinuria. Other clinical features are cytopenias caused by bone marrow failure and an increased risk of thrombosis. If unrecognized and not treated appropriately, PNH is often associated with a substantial morbidity and mortality. PNH is caused by the expansion of a hematopoietic progenitor cell that caries a somatic mutation in the X-linked phosphatidylinositol glycan complementation group A (PIGA) gene. The PIGA gene encodes a protein essential in the biosynthesis of glycosylphosphatidylinositol (GPI)-anchor molecules. A proportion of blood cells from patients with PNH is therefore deficient in all GPI-linked surface proteins. Considerable progress in the field of PNH research in the last 7 years has resulted from the cloning of the PIGA gene. The purpose of the current article is to describe the structure and function of the PIGA gene, to summarize the lessons learned from the analysis of PIGA gene mutations, to review the impact of mouse models on our current understanding of the human disease, and to discuss the possible pathogenesis of PNH. In addition, we will outline novel approaches to PNH diagnosis, research, and therapy that became available thanks to the cloning of the PIGA gene.

[Paroxysmal nocturnal hemoglobinuria: pathogenic and therapeutic news]

Paroxysmal Nocturnal Haemoglobinuria (PNH) is a clinical manifestation of an haemathology cell disease, whose etiology has been unknown for many years. We try to resume the most relevant facts of this entity and to define the pathogenesis which is responsible of the clinical manifestations of the disease.

Successful application of nonmyeloablative transplantation for paroxysmal nocturnal hemoglobinuria

OBJECTIVE

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal hematopoietic stem cell disorder that manifests as hemolytic anemia, venous thrombosis, and deficient hematopoiesis. Although allogeneic hematopoietic stem cell transplantation is considered the only curative therapeutic measure, transplant-related mortality is not negligible. Several studies supported the use of nonmyeloablative stem cell transplantation (NST) for patients of advanced age or with organ dysfunction. Hence, we used NST in a PNH patient who suffered from acute renal failure due to repeated episodes of hemolysis.

MATERIALS AND METHODS

We performed NST using a conditioning regimen consisting of cladribine 0.11 mg/kg x 6, busulfan 4 mg/kg x 2, and rabbit anti-thymocyte globulin 2.5 mg/kg x 2. He received peripheral blood stem cells from his human leukocyte antigen-matched brother. Prophylaxis against graft-vs-host disease was performed with cyclosporine A alone. Chimerism of peripheral blood mononuclear cells was evaluated serially using short tandem repeat analysis and flow cytometry.

RESULTS

No meaningful regimen-related toxicities were documented. Donor chimerism of 90 to 100% was achieved on day 14 and thereafter. The patient is doing well, without any recurrence of hemolysis 6 months after transplant. Follow-up chimerism studies confirmed stable and functioning donor-type hematopoiesis.

CONCLUSIONS

NST may become a safe and curative approach in patients with PNH. Further studies are needed to establish the role of NST for treatment of PNH.

Relative increase of granulocytes with a paroxysmal nocturnal haemoglobinuria phenotype in aplastic anaemia patients: the high prevalence at diagnosis

To clarify the pathologic significance of granulocytes exhibiting the paroxysmal nocturnal haemoglobinuria (PNH) phenotype in patients with aplastic anaemia (AA), we examined peripheral blood from 100 patients with AA for the presence of granulocytes deficient in glycosylphosphatidylinositol (GPI)-anchored proteins using a sensitive flow cytometric assay. A significant increase in the frequency of CD55-CD59-CD11b+ granulocytes (>0.003%) compared to normal individuals was observed in 31 of 35 (88.6%) patients with untreated AA at diagnosis. The proportions of patients showing increased PNH granulocytes in treated AA patients with a short (<5 yr) and long (>5 yr) disease duration were 68.6% (11/16) and 20.4% (10/49), respectively. When 19 patients showing increased frequency of PNH granulocytes before therapy were studied 6-12 months after antithymocyte globulin plus cyclosporin A therapy, the frequency decreased to 0.01-90% of pretreatment values in 15 recovering patients. These findings suggest that a relative increase in the number of PNH granulocytes is a common feature of AA at diagnosis, and that it may represent the presence of immunologic pressure to normal haematopoietic stem cells as a cause of AA.

Successful unrelated donor bone marrow transplantation for paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal disease of hematopoiesis due to a mutation in the PIG-A gene. Affected patients may demonstrate hemolysis or venous thrombosis, and may develop MDS or aplastic anemia. Successful results may be obtained after conditioning and transplantation from syngeneic or genotypically matched sibling donors. Experience with transplantation from matched unrelated donors (MUD) is limited to eight patients, with only one survivor. We report three patients who underwent successful MUD BMT for PNH. All three patients had severe aplastic anemia (SAA) and PNH at the time of BMT. Unrelated donors were six-antigen HLA-matched (n = 2) or HLA-A mismatched (n = 1). Conditioning consisted of cytarabine, cyclophosphamide, TBI, and ATG. Grafts were T cell-depleted by anti-CD6/CD8 antibodies + complement. Further GVHD prophylaxis consisted of cyclosporine. Patients received 0.7-1.1 x 10(8) nucleated cells/kg and 1.1-2.1 x 10(6) CD34(+) cells/kg. Neutrophil engraftment occurred at 16-21 days. One patient developed grade 1 acute GVHD. Although all three patients experienced significant transplant-related complications, they ultimately resolved and all patients are alive and well 30-62 months after BMT. T cell-depleted MUD BMT is an effective treatment option for PNH-related MDS and SAA.

Paroxysmal nocturnal hemoglobinuria (membrane defect, pathogenesis, aplastic anemia, diagnosis)

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal disorder in which intravascular hemolysis results from the somatic mutation of the totipotent stem cells causing an intrinsic defect in red cell membrane. PNH cells lack glycosylphosphatidylinositol (GPI) anchored membrane proteins. Of these proteins absence of CD 59 (MIRL--membrane inhibitor of reactive lysis, protectin) and CD 55 (DAF--decay accelerating factor) makes the PNH cells abnormally sensitive to the lytic action of complement. The defect appears to be in the somatic mutation of the X-linked PIG-A (phosphatidylinositolglycan A class) gene which participate in an early step of GPI-anchor synthesis. PNH is characterized by recurrent life threatening venous thromboses and an intimate association with aplastic anemia (AA). It seems that PNH always coexists with bone marrow failure (BMF) (37). The possible explanation may be that some GPI-anchored proteins may be a critical target recognized by immune effector cells. PNH clones not possessing these critical GPI-anchored proteins will survive because they are selectively resistant to the autoimmune assault that eliminates most normal clones. The flow cytometry of erythrocytes using anti-CD 59 and anti-CD 59 and anti-CD 55 of granulocytes has been now introduced as a very sensitive and quantitative method of PNH diagnosis able to detect PNH cells even in normal individuals (1,54). Thus it seems now clear that we must make distinction between the detection of very occasional PNH cells in patients with BMF and PNH as a clinicohematological entity. Unfortunately, we do not know the minimal content of PNH cells required to produce clinical signs of PNH (38).

[Stem cell transplantation for paroxysmal nocturnal hemoglobinuria]

Paroxysmal nocturnal hemoglobinuria (PNH) represents a rare clonal disorder of hematopoiesis clinically characterized by acquired hemolytic anemia, intravascular hemolysis, hemoglobinuria and frequent occurrence of venous thrombosis. Stem cell transplantation is indicated in patients with severe bone marrow aplasia, repeated massive hemolysis or recurrent life threatening thrombotic complications. Almost 90 transplanted patients with PNH have been published. We report a case of successful allogeneic peripheral blood stem cell transplantation performed in a 24 years old woman with a severe form of PNH with frequent episodes of massive intravascular hemolysis. The patient is now alive completely engrafted 900 days after transplantation without signs of chronic GVHD and without recurrent infections. This case represents the first successfully transplanted patient with PNH in our country.

Cell cycling stress in the monocyte line as a risk factor for progression of the aplastic anaemia/paroxysmal nocturnal haemoglobinuria syndrome to myelodysplastic syndrome

Severe aplastic anaemia (SAA) causes permanent stem cell damage from which patients do not recover after treatment with antilymphocyte globulin (ALG). To produce peripheral blood values compatible with life, the few remaining stem and precursor cells are put under stress. We defined a 'stress factor' (SF) for various haematopoietic lines as the ratio of the corresponding peripheral blood (PB) value to the total colony number in short-term bone marrow cultures from 86 patients with different outcomes. Both values are expressed as percentage of normal, hence SF averages 1 in normal steady-state haematopoiesis. SF was elevated in all patients, from 2-to 40-fold, with wide variations in different patient groups and striking differences between haematopoietic lineages. In long-term disease-free survivors after ALG (group 1) the mean total colony count was 19% of normal, with a significantly higher proportion of erythroid burst-forming units compared to normal. They had ineffective erythropoiesis with haemoglobin (Hb) values below, and reticulocyte counts above normal; platelet counts were 67% of normal. In contrast, monocyte counts were in the high normal range, resulting in a high SF (18.7 +/- 1.9) for monocytes. In patients who developed paroxysmal nocturnal haemoglobinuria (PNH) after ALG (group 2), ineffective erythropoiesis, reflecting haemolysis, was more pronounced and they had striking relative monocytosis, resulting in a significantly higher SF for monocytes (33.7 +/- 5.7) compared with group 1 (p < 0.0001). High monocyte counts most likely reflect the relative resistance of nucleated cells to complement, compared with red cells and platelets. Patients who developed myelodysplastic syndrome (MDS) or acute myeloid leukaemia (AML) after ALG, with or without PNH (group 3), had the highest SF for monocytes (39 +/- 10). They also had neutrophil counts in the upper range, or above normal, resulting in a high SF for neutrophils: 32 +/- 19. In patients with persisting or relapsing-remitting pancytopenia without a clinically detectable clonal disorder (group 4), all values were strikingly similar to those of the PNH group. In patients who achieved normal PB values after uncomplicated bone marrow transplantation (group 5), the SF averaged 3, but they also had ineffective erythropoiesis and mild relative monocytosis, a possible sign of occult PNH. We conclude that all patients after treatment of SAA have ineffective erythropoiesis and relative monocytosis, and that these abnormalities probably reflect PNH. We suggest that the resulting high SF for the leukocyte - particularly the monocyte line - predisposes to the development of MDS/AML. We discuss how these results may provide some of the missing pieces in the puzzle of SAA/PNH.

Bone marrow transplantation for paroxysmal nocturnal hemoglobinuria

BACKGROUND AND OBJECTIVE

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal disease of the hemopoietic stem cell (HSC) characterized by intravascular hemolysis and increased risk of venous thrombosis. There are different therapeutic approaches for PNH which do not cure the disease, but can decrease its complications. Allogeneic bone marrow transplantation (BMT) may cure PNH. We reports here our experience of seven PNH patients who underwent allogeneic BMT.

DESIGN AND METHODS

Between January 1991 and January 1999 seven patients with PNH, aged 23 to 37, were transplanted with unmanipulated bone marrow from HLA identical siblings. Median time from diagnosis to BMT was 2.5 years (range: 1-16). All patients were transfusion-dependent and had received various treatments before BMT: steroids, vitamins, cyclosporin A (CyA), growth factors. One patient had also been treated with anti-thymocyte globulin. One patient was HbsAg positive and one anti-HCV positive. At the time of BMT the median value of hemoglobin (Hb) was 9 g/dL (range 6.5-11), white blood cells 5&10(9)/L (range: 2.9-7.7), platelets 97&10(9)/L (range: 31-355), LDH: 2726 U/L. The conditioning regimen was cyclophosphamide (160 mg/kg) and busulfan (10-14 mg/kg), followed by unmanipulated bone marrow (median of 5&10(8) cells/kg) and CyA (+MTX in two patients) for prophylaxis of graft-versus-host disease (GvHD).

RESULTS

All seven patients are alive, full chimeras, with complete hematologic recovery and no evidence of PNH, at a median follow up of 51 months post-BMT (6-103). Time to achieve a granulocyte count of 0.5&10(9)/L, platelets 30&10(9)/L and Hb 10 g/dL was respectively 16, 19 and 22 days. Acute GvHD was limited or mild in six patients, and severe in one. Chronic GvHD was extensive in two patients.

INTERPRETATION AND CONCLUSIONS

This study confirms that HLA identical sibling BMT is an effective therapeutic option for PNH, also in the hemolytic phase of the disease: it also suggests that HBV and HCV infections are not an absolute contraindication.

Bone marrow transplantation for paroxysmal nocturnal haemoglobinuria

Paroxysmal nocturnal haemoglobinuria (PNH) is an acquired clonal disorder of the haemopoietic stem cells for which the only curative treatment is bone marrow transplantation. There are few reports on the use of allogeneic transplantation for PNH, and nearly all of them include only a few patients. Between September 1978 and December 1997, 16 patients underwent marrow transplantation for PNH at the Hospital Saint Louis. The 5-year survival rate for the 16 patients was 58 +/- 13%. Two factors, an absolute neutrophil count >1.0 x 109/l and haemoglobin level >9 g/dl at transplant, were found to be statistically associated with a better outcome.

[Effective treatment combining antithymocyte globulin, cyclosporin A, and granulocyte colony-stimulating factor for atypical paroxysmal nocturnal hemoglobinuria accompanied by bone marrow hypoplasia]

A 25-year-old man was admitted for evaluation of pancytopenia on May 2, 1997. On admission, he had pancytopenia with a normal reticulocyte count. Bone marrow aspirate specimens displayed a normal karyotype and hypocellularity without myelodysplasia. Although total bilirubin and lactate dehydrogenase levels were within their normal ranges, the haptoglobin level was low; additionally, two-color flow cytometric analysis determined that 3.3% of erythrocytes were double-negative for CD55 and CD59 expression. Atypical paroxysmal nocturnal hemoglobinuria with bone marrow hypoplasia was diagnosed. Because initial treatment with cyclosporin A was not effective, the patient was subsequently given a combination of antithymocyte globulin, cyclosporin A, and granulocyte colony-stimulating factor. Although the pancytopenia subsided, the percentage of double-negative erythrocytes in the patient's blood remained almost unchanged compared to findings obtained on admission.

Bone marrow transplants for paroxysmal nocturnal haemoglobinuria

Paroxysmal nocturnal haemoglobinuria (PNH) is a rare clonal haematological disorder characterized by intravascular haemolysis and increased risk of thrombosis. PNH is associated with bone marrow failure syndromes including aplastic anaemia, myelodysplasia and leukaemia. Bone marrow transplants are sometimes used to treat PNH, but small series and reporting biases make assessment of transplant outcome difficult. The outcome of 57 consecutive allogeneic bone marrow transplants for PNH reported to the International Bone Marrow Transplant Registry (IBMTR) between 1978 and 1995 was analysed. The 2-year probability of survival in 48 recipients of HLA-identical sibling transplants was 56% (95% confidence interval 49-63%). Two recipients of identical twin transplants remain alive 8 and 12 years after treatment. One of seven recipients of alternative donor allogeneic transplants is alive 5 years after transplant. The most common causes of treatment failure were graft failure and infections. Our results indicate that bone marrow transplantation can restore normal bone marrow function in about 50% of PNH patients.

Paroxysmal nocturnal haemoglobinuria: the disease and a hypothesis for a new treatment

Paroxysmal nocturnal haemoglobinuria (PNH) is a disease entity that presents with intravascular haemolysis and an increased tendency for venous thrombosis. In recent years there has been a major breakthrough in our understanding of the pathogenesis of PNH. Most of the different symptoms can be tracked down to the deficiency of glycophosphoinositol (GPI)-anchored proteins in cell lines deriving from a single haematopoietic stem cell. This deficiency is caused by a mutation in the X-chromosomal PIG-A gene whose product, a glycosyltransferase, participates in the first step of the GPI-anchor biosynthesis. Lack of GPI-linked complement inhibitors CD55 and CD59 predisposes red blood cells to lysis. The main unresolved question is why the stem cells lacking GPI-anchored surface proteins gain a growth advantage over their normal counterparts. So far, our progress in understanding the pathogenesis has not resulted in better treatment of PNH and new ideas are warranted. In this regard, we propose a new mode of treatment for PNH by exploiting the increased susceptibility of affected bone marrow precursor cells to complement and targeting complement attack against them by a specific complement-activating monoclonal antibody.

Paroxysmal nocturnal hemoglobinuria: molecular pathogenesis and molecular therapeutic approaches

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal hematologic stem cell disorder classified as an intravascular hemolytic anemia. Abnormal blood cells are deficient in glycosylphosphatidyl inositol (GPI)-anchored proteins. Deficiencies of GPI-anchored complement regulatory proteins, such as decay accelerating factor (DAF) and CD59, render red cells very sensitive to complement and result in complement-mediated hemolysis and hemoglobinuria. In the affected hematopoietic cells from patients with PNH, the first step in biosynthesis of the GPI anchor is defective. Three genes are involved in this reaction step and one of them, an X-linked gene termed PIG-A, is mutated in affected cells. Granulocytes and lymphocytes from the same patient have the same mutation, indicating that a somatic PIG-A mutation occurs in hematopoietic stem cells. The PIG-A gene is mutated in all patients with PNH reported to date. We review these recent advances in the understanding of the molecular pathogenesis of PNH. Furthermore, we present an hypothesis regarding the predominance of the PNH clone, caused by positive selection by hematopoietic suppressive cytokines, such as transforming growth factor (TGF)-beta. In addition, we discuss the possibility of cure for PNH through molecular therapeutic strategy using gene transfer techniques. (Key words: paroxysmal nocturnal hemoglobinuria, glycosylphosphatidylinositol-anchored proteins, PIG-A, clonal dominance, growth advantage, transforming growth factor-beta, gene therapy, molecular therapeutic approach).

Paroxysmal cold haemoglobinuria of childhood: a review of the management and unusual presenting features of six cases

We report six cases of children presenting with paroxysmal cold haemoglobinuria occurring in a 3-year period in the north-west of England. In all six cases the onset of the illness was dramatic and its duration brief. We note the prominent red cell agglutination was evident in the blood film, the absence of a prompt reticulocyte response and a negative classical direct Donath Landsteiner test in each of these cases. The Direct Coombs Test (DCT) was positive when anticomplement reagents were used but high titres of free autoantibody were not demonstrated in the serum.

New somatic mutation in the PIG-A gene emerges at relapse of paroxysmal nocturnal hemoglobinuria

We report a detailed longitudinal study of the first patient to be treated (in 1973) for paroxysmal nocturnal hemoglobinuria (PNH) with syngeneic bone marrow transplantation (BMT). The patient subsequently relapsed with PNH in 1983, and still has PNH to date. Analysis of the PIG-A gene in a recent blood sample showed in exon 6 an insertion-duplication causing a frameshift. Polymerase chain reaction (PCR) amplification of the PIG-A exon 6 from bone marrow (BM) slides obtained before BMT showed that the duplication was not present; instead, we found several single base pair substitutions in exons 2 and 6. Thus, relapse of PNH in this patient was not due to persistence of the original clones; rather, it was associated with the emergence of a new clone. These findings support the notion that the BM environment may create selective conditions favoring the expansion of PNH clones.

[Paroxysmal nocturnal hemoglobinuria in pregnancy]

The combination of paroxysmal nocturnal haemoglobinuria (PNH) and pregnancy occurred in three women aged 29, 31 and 35 years. One patient had a spontaneous abortion twice after which she committed suicide. In the other two the pregnancy and parturition--assisted--were without complications. However, one woman developed post-partum abdominal crises. The children were born at term and healthy. PNH is a rare form of haemolytic anemia. Pregnancy causes lethal complications in 6% of the cases of PNH, while 30% of the pregnancies end in spontaneous abortion or stillbirth. Accurate monitoring of pregnancy and the puerperium is essential.