Paroxysmal nocturnal hemoglobinuria (PNH)


A rare but potentially fatal hematopoetic stem cell disease caused by a mutation in the PIG-A gene that convers sensitivity to complement-mediated lysis to all blood cell lineages.

Characterized by the triad of intravascular hemolysis, high risk for thrombosis, and some degree of bone marrow impairment.

Estimated incidence about 2.6 per million, and less than 10 cases per million population prevalence.

A prototypical nonmalignant clonal disorder.

Can involve patient of any age, but occurs mainly in young adults.

Median age at diagnosis in the early 30s.

Somatic mutation of the PIG-A gene in a hematopoietic cell line.

It is caused by loss of function mutation in PIGA.

An acquired mutation of the PIG-a gene on the X chromosome that encodes glycosyl-phosphatidylinositol.

This somatic mutation makes a mutant hematopoietic stem cell and its progeny are unable to synthesize the glycosyl-phosphatidylinositol anchor, which serves to tether a number of proteins to the cell membrane.

PNH is caused by the expansion of hematopoietic stem cells carrying the somatic mutation in PIGA, which includesphosphatidylinositol N-acetyl glucoseaminotransferase, sub unit A.

Two of these proteins, CD 55 and CD 59, protect cells from activated complement, and their absence from the surface of PNH cells makes them susceptible to complement activation resulting in hemolysis.

PNH results from abnormal hematopoetic clone expansion that lacks cell-surface complement inhibitory proteins attached to the membrane through Glycosyl-phosphatidylinositol  anchors.

Glycosyl-phosphatidylinositol is a structural anchor for a number of cell surface proteins.

Mutations of the PIG-A gene disrupt the first step of glycophosphatidylinositol biosynthesis, which leads to an absence of GPI anchor and deficiency of GPI linked proteins.

Flow cytometry of glycosyl phosphatidylinositol-anchored protein expression on peripheral blood cells (both RBC & Granulocytes) and marrow analysis are required for disease classification.

In PNH, somatic mutation of the PIGA gene in a hematopoetic stem cell causes deficiency of a glycophosphatidylinositol in its progeny cells: as a result, excessive activation of the complement system occurs on the surface of the affected blood cells, resulting in intravascular hemolysis and thrombosis.

In patients with suspected PNH high sensitivity flow cytometry can detect as few as 0.01% of cells with the characteristic GPI-anchor deficit.

Progeny of affected stem cells are deficient in glycosyl phosphatidylinositol-anchored proteins.

Deficiency of glycosyl phosphatidylinositol-anchored complement regulatory proteins CD55 and CD59 accounts for intravascular hemolysis which is the primary clinical manifestation.

Expansion of the PNH clone leads to a large percentage of blood cells missing complement regulatory proteins CD55 and CD59: leading to intravascular hemolysis and risk for venous and arterial thrombosis.
Clonal expanded red blood cells that lack ability to inhibit complement mediated hemolysis resulting in red blood cell destruction, anemia and thromboses.
Complement dysregulation leads to chronic hemolysis and thrombosis seen in PNH.
Hemolysis manifestations in PNH is due directly to the increased sensitivity of PNH red blood cells to complement.
I/n patients with untreated PNH intravascular hemolysis is continuous and can be attributed to low-grade complement activation by means of spontaneous hydrolytic activation of C3 known as the trick over mechanism.
Paroxysms of hemolysis occur when complement activation is more risk, such as in the course of infection.

Paroxysmal nocturnal hemoglobinuria (PNH) associated with a risk for Budd-Chiari syndrome, more than other forms of thrombophilia: up to 39% develop venous thromboses, and 12% may acquire Budd-Chiari.

Historically thrombosis has been the leading cause of death in PNH and quality of life has been poor due to anemia, fatigue, and smooth muscle dystonias.

Intravascular hemolysis, in addition to causing anemia, results in smooth muscle dystonia with abdominal pain, dysphasia, and erectile dysfunction likely caused by local nitric oxide depletion due to the binding of nitric oxide to plasma hemoglobin, and a high risk of thrombosis.

About 10%-20% of patients with aplastic anemia evolve into PNH.

It is suspected that PNH and aplastic anemia arise from overlapping etiologies.

Complement dependent intravascular hemolytic anemia, and bone marrow failure.

Presentation includes extravascular hemolysis, marrow failure and thrombophilia.

Patients present with fatigue, dyspnea, abdominal pain, dark urine, trouble swallowing, renal insufficiency, and pulmonary hypertension.

97% of PNH patients have fatigue, 66% dyspnea, and 59% have abdominal pain.

64% of patients with PNH have chronic renal insufficiency, and almost 50% have evidence of pulmonary hypertension, while 76% have disruptions in their daily activities.

About 90% of patients have a concomitant cytopenias.

Hypoplastic disease is associated with a clone size that is less than 20% of classical patients with a background of bone marrow failure.

Commonly associated with hemoglobinuria, dysphagia, odynophagia and male impotence.

Release of free hemoglobin results in hemoglinuria, anemia, , abdominal pain, dysphagia, pulmonary hypertension, renal impairment and erectile dysfunction.

Only 26% of newly diagnosed unclassified patients present with hemoglobinuria.

All patients with significant clinical hemolysis have an elevated LDH as a result on intravascular complement mediated hemolysis.

Essentially all patients with classic PNH report gross hemoglobinuria at some point in their clinical process, but it may be absent in PNH/aplastic anemia or PNH/refractory anemia-MDS because of a small clone size.

During sleep the lowering of the pH triggers activation of complement dependent hemolysis.

Thrombosis of hepatic vein occurs in up to on third of patients with PNH.

Thrombosis occurs in approximately 50% of patients.

Unexplained thrombosis patients are in high-risk for PNH.

Patients with PNH are at risk for arterial and venous thromboembolism.

Patients at high risk for atypical site venous thromboembolism include Budd-Chiari syndrome, renal, and dermal thrombosis.

Almost 40% of thrombotic events in patients with PNH occur in arterial sites.

The age of onset of ischemic stroke in patients with PNH is 46 years compared to the general population of 73 years.

Associated with chronic hemolysis with periods of exacerbations with increased symptoms.

Wide spectrum of disease with classic hemolytic disease separated from hypo plastic or aplastic anemia associated PNH.

With classic PNH patients tend to have a large PNH clone of granulocytes of greater than 30% and erythrocytes of greater than 7% and typical symptoms of hemoglobulinuria, and infections, elevated LDH reticulocyte count, normo to hypercellular activity in the marrow and mild to moderate cytopenias.

Hypoplastic PNH patients present with bone marrow failure or aplastic anemia with smaller populations of NH granulocytes of less than 20% and less than 3% with a hypocellular bone marrow and moderate to severe cytopenias, with a decreased reticulocyte count and normal LDH levels.

Loss of expression of CD 55 and CD 59 on RBC’s, because of gene mutation, prevents inhibition of complement mediated erythrocyte lysis.

Decay accelerating factor (CD55) is a cell surface protein which prevents hemolysis by impairing assembly of the complement cascade on the erythrocyte membrane.

Can present with pancytopenia secondary to underlying bone marrow failure, and can progress to acute myelogenous leukemia or myelodysplasia syndrome.

Red blood cells with the PNH phenotype are susceptible to complement mediated lysis, as demonstrated by the Ham’s test.

Because it involves clonal expansion of mutated cells the early phase of the disease has few or no symptoms.

As the clinal population expands many patients experience fatigue, headache, abdominal pain, and episodes of dark urine.

Diagnosis by flow cytometry of peripheral blood, which also can quantify size of the PNH clone.

It can take months, and sometimes years, to receive a correct diagnosis for PNH, a chronic, progressive and potentially life-threatening rare disease.

The presence of PNH Cells is associated with the superior response to immunotherapy.

Early diagnosis by flow cytometry is essential for improving prognosis.

Median survival 10-15 years, with more recent studies indicate 22 year median survivorship.

Bone marrow transplantation is the mainstay of treatment.

Optimal management requires defining the contribution of hemolysis and bone marrow failure to complex anemia.

Thrombosis of unusual sites such associated the liver, skin, brain, and mesentery characteristic of PNH thrombophilia.

Following a thromboembolic event long term anticoagulation is recommended.

Thrombolytic therapy should be considered in the presence of hepatic vein (Budd-Chiari syndrome).

Thrombosis is main cause of death, and accounts for approximately one third of deaths.

Thrombosis In pregnant patients requires the use of prophylactic anticoagulation treatment.

Classical PNH-clinical evidence for intravascular hemolysis with reticulocytosis, high LDH levels, indirect hyperbilirubinemia, and low levels of haptoglobin without other defined bone marrow disorder.

PNH with another specified bone marrow disorder-clinical evidence of hemolysis with a history of a defined underlying bone marrow abnormality such as aplastic anemia, myelodysplastic disorder or other myelopathy such as myelofibrosis.

Subclinical PNH-patients have no clinical or laboratory evidence of hemolysis but have small numbers of glycosyl phosphatidylinositol anchored deficient cells detected by sensitive cytometric analysis and is associated with bone marrow failure disorders.

Screening should be done on patients with hemoglobinuria, patients with Coombs-negative intravascular hemolysis (based on high LDH), patients who present with venous in unusal sites, patients with aplastic anemia, MDS, and/or episodic dysphagia or abdominal pain with evidence of intravascular hemolysis.

C5 inhibitors prevent terminal complement-mediated platelet and white cell activation and destruction, leading to a marked  reduction in thrombosis, which is the main life-threatening complication of PNH.
C5 inhibition ameliorate anemia and reduces the need for transfusions and prevents many PNH complications such as kidney failure and pulmonary hypertension.
Intravascular hemolysis is largely abrogated when C5 is blocked by monoclonal antibodies, like eculizumab, and it has been a major advance in the management of PNH resulting in remarkable clinical improvements, including relief from anemia, reduction of thrombotic risk, improved quality of life, and prolonged survival.

PNH erythrocytes also lack CD55, leading to reduction of C3-convertase enzyme dissociation, increasing the production of C3 fragments and subsequent opsonization.

Intravenous anti-C5 Monical antibodies became the standard treatment for hemolytic PNH in 2007.

Eculizumab (Soliris) a humanized monoclonal antibody that targets and prevents cleavage of the terminal complement protein C5 and reduces hemolysis.

Eculizumab binds to the terminal complement proteins C5, it inhibits it’s cleavage into C5a and C5b by C5 convertases and prevents the release of inflammatory mediator C5a and the formation of the cytolytic pore C5b-9.

C5 blockade preserves the immune-protective and immune-regulatory functions that culminate in C3b-mediated opsonization in immune clearance.

Eculizumab reduces hemolysis, stabilizes hemoglobin levels, reduces transfusion requirements, and improves quality of life in patients with PNH.

Eculizumab highly effective in reducing intravascular hemolysis in PNH.

Eculizumab Is effective in preventing C-5-dependent intravascular hemolysis  mediated by the membrane attack complex, however surviving PNH erythrocytes become opsonized with apC3 fragments and are removed by extravascular hemolysis in the liver and spleen. 
Breakthrough hemolysis may be attributed to suboptimal C5 inhibition due to low levels of a eculizumab or when infection or inflammation causes strong complement activation and breaks through the C5 blockade.

Extravascular hemolysis is seen in most patients with PNH treated with C5 Inhibitors and leads to reduced RBC half-life to 10-13 days: contributing to persistent anemia despite C-5 inhibitor treatment.

Eculizumab protects against complications of hemolysis such as impaired renal function, pulmonary HT, and thromboembolism.

Eculizumab Is an intravenous monoclonal antibody that binds to C5 and prevents formation of the membrane attack complex improving anemia, reducing thrombosis risk, improving quality of life, and improve survival age match controls.

In a study of 79 consecutive PNH patients treated with this agent survival was not different from age and sex matched normal controls, and was significantly better than 30 patients managed before this agent (Kelly RJ et al).

Ravulizumab (Ultomiris) approved for adults with PNH and was not inferior to eculizumab.

Ravulizumab (Ultomiris) also approved for pediatric patients with PNH.
Because review Ravulizumab can be administered every eight weeks it has become the new standard of care for PNH.
Over 75% of patients on C-5 inhibitors achieve a good hemoglobin level with minimal or no symptoms, but a minority remains severely anemic and require transfusion due to extravascular hemolysis.
Pegcetacoplan, a pegylated peptide targeting proximal complement protein C3, potentially inhibits both intravascular and extravascular hemolysis: it was superior to eculizumab in improving hemoglobin and clinical and hematologic outcomes and patients with PNH by providing broad hemolysis control, including control of intravascular and extravascular hemolysis.

Pegcetacoplan (Empaveli) is approved for the treatment of adults with paroxysmal nocturnal hemoglobinuria who are treatment naive and those who are switching from the C5 inhibitors eculizumab (Soliris) and ravulizumab.

Pegcetacoplan blocks complemented C3 and is administered  subcutaneously over 30 minutes twice a week.

Iptacopan , is a medication used for the treatment of paroxysmal nocturnal hemoglobinuria.

Iptacopan is an oral, proximal complement inhibitor the targets factor be in the alternative pathway and abrogates extravascular hemolysis and maintains intravascular Mall assist control in patients with PNH and persistent anemia, despite anti-C-5 treatment and controls intravascular hemolysis control without causing extravascular hemolysis in patients who had not received the complement inhibitor in the three months before treatment.


Leave a Reply

Your email address will not be published. Required fields are marked *