Paroxysmal nocturnal haemoglobinuria: nature's gene therapy?

CD59 gene: 143 haplotypes of 22,718 nucleotides length by computational phasing in 113 individuals from different ethnicities

BACKGROUND

CD59 deficiency due to rare germline variants in the CD59 gene causes disabilities, ischemic strokes, neuropathy, and hemolysis. CD59 deficiency due to common somatic variants in the PIG-A gene in hematopoietic stem cells causes paroxysmal nocturnal hemoglobinuria. The ISBT database lists one nonsense and three missense germline variants that are associated with the CD59-null phenotype. To analyze the genetic diversity of the CD59 gene, we determined long-range CD59 haplotypes among individuals from different ethnicities.

METHODS

We determined a 22.7 kb genomic fragment of the CD59 gene in 113 individuals using next-generation sequencing (NGS), which covered the whole NM_203330.2 mRNA transcript of 7796 base pairs. Samples came from an FDA reference repository and our Ethiopia study cohorts. The raw genotype data were computationally phased into individual haplotype sequences.

RESULTS

Nucleotide sequencing of the CD59 gene of 226 chromosomes identified 216 positions with single nucleotide variants. Only three haplotypes were observed in homozygous form, which allowed us to assign them unambiguously as experimentally verified CD59 haplotypes. They were also the most frequent haplotypes among both cohorts. An additional 140 haplotypes were imputed computationally.

DISCUSSION

We provided a large set of haplotypes and proposed three verified long-range CD59 reference sequences, based on a population approach, using a generalizable rationale for our choice. Correct long-range haplotypes are useful as template sequences for allele calling in high-throughput NGS and precision medicine approaches, thus enhancing the reliability of clinical diagnostics. Long-range haplotypes can also be used to evaluate the influence of genetic variation on the risk of transfusion reactions or diseases.

A Review of Systemic Hematological Manifestations and Stent Thrombosis

Stent thrombosis (ST) has significant morbidity and mortality following percutaneous coronary intervention (PCI). ST is uncommon making the identification of nonprocedural predictors challenging. Numerous case reports of ST in both benign and malignant hematological conditions exist. Given ST could be a Herald event of an undiagnosed condition and condition-specific treatment may be available, it is important to consider specialist testing in an unexplained ST. This review included a case presentation of ST in previously undiagnosed paroxysmal nocturnal hemoglobinuria (PNH) and a literature review of ST in other acquired thrombophilias including myeloproliferative disorders (MPNs), antiphospholipid syndrome, hematological malignancies, and heparin-induced thrombocytopenia (HIT). Inherited thrombophilias and common pitfalls in thrombophilia and coagulation testing are also discussed. The cardiac-hematology landscape is becoming increasingly complex and there is a paucity of how to best manage ST in these patients. There is clear variability in practice and the use of multidisciplinary input between cardiologists and hematologists is essential.

Early frameshift mutation in PIGA identified in a large XLID family without neonatal lethality

The phosphatidylinositol glycan class A (PIGA) protein is a member of the glycosylphosphatidylinositol anchor pathway. Germline mutations in PIGA located at Xp22.2 are thought to be lethal in males. However, a nonsense mutation in the last coding exon was recently described in two brothers with multiple congenital anomalies-hypotonia-seizures syndrome 2 (MCAHS2) who survived through birth likely because of the hypomorphic nature of the truncated protein, but died in their first weeks of life. Here, we report on a frameshift mutation early in the PIGA cDNA (c.76dupT; p.Y26Lfs*3) that cosegregates with the disease in a large family diagnosed with a severe syndromic form of X-linked intellectual disability. Unexpectedly, CD59 surface expression suggested the production of a shorter PIGA protein with residual functionality. We provide evidence that the second methionine at position 37 may be used for the translation of a 36 amino acids shorter PIGA. Complementation assays confirmed that this shorter PIGA cDNA was able to partially rescue the surface expression of CD59 in a PIGA-null cell line. Taken together, our data strongly suggest that the early frameshift mutation in PIGA produces a truncated hypomorph, which is sufficient to rescue the lethality in males but not the MCAHS2-like phenotype.

In vivo mutation analysis using the ΦX174 transgenic mouse and comparisons with other transgenes and endogenous genes

The ΦX174 transgenic mouse was first developed as an in vivo Ames test, detecting base pair substitution (bps) at a single bp in a reversion assay. A forward mutational assay was also developed, which is a gain of function assay that also detects bps exclusively. Later work with both assays focused on establishing that a mutation was fixed in vivo using single-burst analysis: determining the number of mutant progeny virus from an electroporated cell by dividing the culture into aliquots before scoring mutants. We review results obtained from single-burst analysis, including testing the hypothesis that high mutant frequencies (MFs) of G:C to A:T mutation recovered by transgenic targets include significant numbers of unrepaired G:T mismatches. Comparison between the ΦX174 and lacI transgenes in mouse spleen indicates that the spontaneous bps mutation frequency per nucleotide (mf(n)) is not significantly lower for ΦX174 than for lacI; the response to ENU is also comparable. For the lacI transgene, the spontaneous bps mf(n) is highly age-dependent up to 12 weeks of age and the linear trend extrapolates at conception to a frequency close to the human bps mf(n) per generation of 1.7 × 10(-8). Unexpectedly, we found that the lacI somatic (spleen) bps mf(n) per cell division at early ages was estimated to be the same as for the human germ-line. The bps mf(n) in bone marrow for the gpt transgene is comparable to spleen for the lacI and ΦX174 transgenes. We conclude that the G:C to A:T transition is characteristic of spontaneous in vivo mutation and that the MFs measured in these transgenes at early ages reflect the expected accumulation of in vivo mutation typical of endogenous mammalian mutation rates. However, spontaneous and induced mf(n)s per nucleotide for the cII gene in spleen are 5-10 times higher than for these other transgenes.

The platelet function defect of paroxysmal nocturnal haemoglobinuria

Paroxysmal nocturnal haemoglobinuria (PNH) is a rare, acquired stem cell disorder, characterised by an abnormal susceptibility of red blood cells to complement induced lysis, resulting in repeated episodes of intravascular haemolysis and haemoglobinuria, thromboembolic events at atypical locations and, to a much lesser extent, bleeding complications. Platelet function is assumed to be abnormal, however, a defect has not yet been characterised and underlying mechanisms remain elusive. To explore these issues, we investigated platelet function in PNH patients using assays for clot formation under low and high shear force (thrombelastography and PFA100 device), adhesion to glass beads in native whole blood (Hellem method), aggregometry using various agonists (Born method), and flow cytometric assays for baseline and agonist-induced surface expression density of alpha-granule (CD62P) and lysosomal granule proteins (CD63), ligand binding to surface receptors (thrombospondin), and expression density of activation-induced neoepitopes of the fibrinogen receptor complex (PAC-1). Platelet PNH clone size determined by CD55 and CD59 labelling was compared to the clone sizes of granulocytes, monocytes, erythrocytes, and reticulocytes. A profound reduction of platelet reactivity was observed in PNH patients for all "global function" assays (clot formation, adhesion, aggregation). Platelet hyporeactivity was confirmed using flow cytometric assays. Whereas baseline levels of flow cytometrically determined platelet activation markers did not differ significantly between controls and PNH patients, agonist-induced values of all markers were distinctly reduced in the PNH group. Moreover, significantly reduced white blood cell counts (3.1/nl vs. 5.9/nl), haemoglobin values (9.5 vs. 14.3/g per dl), and platelet counts (136 vs. 219/nl) delineate profound tricytopenia in PNH patients. The fraction of particular cell types lacking the surface expression of GPI-anchored glycoproteins is referred to as the respective PNH clone; median PNH clone sizes of cells with short life spans (reticulocytes, platelets, granulocytes) was 50-80% of total cell populations compared to 20% of red blood cells. The results of our laboratory investigations show, that in PNH, reduced platelet counts coincide with reduced platelet reactivity. The foremost clinical complication in PNH, however, is venous thromboembolism, very probably induced by an activated and dysregulated plasmatic coagulation system. From these seemingly contradictory findings we infer, that part of the platelet hyporeactivity is probably due to reactive downregulation of platelet function in response to chronic hyperstimulation. The overall result is thought to be an unsteady balance, associated with thromboembolism in a larger proportion of patients, and with bleeding in a smaller proportion.

New mutations in C1GALT1C1 in individuals with Tn positive phenotype

Tn polyagglutination results from inactivating mutations in C1GALT1C1, an X-borne gene encoding a core 1 beta3-galactosyltransferase-specific molecular chaperone (cosmc) required for the functioning of T-synthase (beta 1,3-galactosyltransferase), a glycosyltransferase essential for the correct biosynthesis of O-glycans. This study found novel inactivating mutations (Glu152Lys, Ser193Pro and Met1Ile) in the coding sequence of C1GALT1C1 in three Tn positive individuals and a complete lack of C1GALT1C1 cDNA expression was observed in an additional Tn positive individual. In addition, expression of ST6GALNAC1, which encodes (alpha-N-acetyl-neuraminyl-2,3-beta-galactosyl-1, 3)-N-acetylgalactosaminide alpha-2,6-sialyltransferase 1 and gives rise to sialyl-Tn antigen, was present at comparable levels in normal and Tn-positive human erythroblasts. Expression studies of wild-type and Tn positive C1GALT1C1 cDNA in the Jurkat cell line confirmed that the amino acid substitutions observed in Tn are inactivating. Analysis of the transcriptome of cultured normal and Tn positive erythroblasts revealed numerous differences in gene expression. Reduced transcript levels for fatty acid binding protein 5 (FABP5) and plexin D1 (PLXND1), and increased levels for aquaporin 3 (AQP3) were confirmed by quantitative real-time polymerase chain reaction. These data show that alteration of O-glycan structures resulting from T-synthase deficiency is accompanied by altered expression of a wide variety of genes in erythroid cells.

Decay-accelerating factor but not CD59 limits experimental immune-complex glomerulonephritis

The complex balance between the pro-activating and regulatory influences of the complement system can affect the pathogenesis of immune complex-mediated glomerulonephritis (ICGN). Key complement regulatory proteins include decay accelerating factor (DAF) and CD59, which inhibit C3 activation and C5b-9 generation, respectively. Both are glycosylphosphatidylinositol-linked cell membrane proteins, which are widely distributed in humans and mice. Chronic serum sickness induced by daily immunization with horse spleen apoferritin over 6 weeks was used to induce ICGN in DAF-, CD59- and DAF/CD59-deficient mice, with wild-type littermate mice serving as controls. Both DAF and DAF/CD59-deficient mice had an increased incidence of GN relative to wild-type controls associated with significantly increased glomerular C3 deposition. Disease expression in CD59-deficient mice was no different than wild-type controls. DAF- and DAF/CD59-deficient mice also had increased monocyte chemoattractant protein-1 mRNA expression and glomerular infiltration with CD45(+) leukocytes. Our findings suggest that activation of C3 is strongly associated with experimental ICGN while downstream formation of C5b-9 is of lesser pathogenic importance in this model.

Acute renal failure in a patient with severe hemolysis

Paroxysmal nocturnal hemoglobinuria (PNH) is a clonal disorder of bone marrow. It is characterized by blood cells lacking membrane proteins that are normally attached by the glycosylphosphatidylinositol (GPI) anchor. The cellular defect arises in a hematopoetic stem cell and is due to somatic mutation of the Phosphatidylinositol-glycan protein-A gene (PIG-A gene), encoding a protein needed for the biosynthesis of the anchor GPI. Paroxysmal nocturnal hemoglobinuria is presented by intravascular hemolysis, cytopenias, frequent infections, bone marrow hypoplasia, and a high incidence of life threatening venous thrombosis. Kidney involvement is usually benign and secondary to chronic tubular deposition of hemosiderin. Acute renal failure may occur in association with a hemolytic crisis. Here we report a case of 40-year-old woman with hematuria, pancytopenia, and acute renal failure due to PNH.

Unrestricted C3 activation occurs in Crry-deficient kidneys and rapidly leads to chronic renal failure

Deficiency of the C3 convertase regulator Crry is embryonic lethal in mice unless C3 also is absent. For evaluation of the effect of local kidney Crry deficiency in the setting of an intact complement system, Crry(-/-)C3(-/-) mouse kidneys were transplanted into syngeneic C57BL/6 wild-type mice. These Crry-deficient kidneys developed marked inflammatory cell infiltration, tubular damage, and interstitial fibrosis, whereas similar changes were absent in control transplanted kidneys. Strong C3 deposition in the vessels and tubules that correlated significantly with measures of disease supported that complement activation was pathogenic in this model. Microarray studies showed upregulation of a number of chemokine and extracellular matrix genes, which were validated for CCL2 and CXCL10 mRNA and collagen III protein. The functional significance of these pathophysiologic findings was evaluated by removing both native kidneys, so the transplanted kidney alone provided renal function. Within 21 d of transplantation, seven of eight Crry-deficient kidneys in complement-sufficient wild-type hosts failed, compared with two of 13 controls (P = 0.001), with final blood urea nitrogen levels of 133.9 +/- 33.0 and 55.6 +/- 8.3 mg/dl, respectively (P = 0.015). These data show that mouse Crry is a critical complement regulator in the kidney. When absent, unrestricted complement activation occurs and quickly leads to marked inflammation and progressive renal failure, with features relevant to human diseases with underlying defects in complement regulation, such as hemolytic uremic syndrome.

PIG-A mutations in paroxysmal nocturnal hemoglobinuria and in normal hematopoiesis

PIG-A is an X-linked gene that is essential for the first step in the biosynthesis of glycosylphosphatidyl-inositol (GPI) anchors. A rare clonal hematopoietic stem cell disease, paroxysmal nocturnal hemoglobinuria (PNH), is caused by mutations in the PIG-A gene. PNH is an acquired disease that may arise de novo or emanate from aplastic anemia. PNH blood cells have an absence or marked deficiency of all GPI anchored proteins. Interestingly, rare GPI anchor deficient blood and marrow cells that harbor PIG-A mutations can also be found in most healthy controls. This review examines the clinical and biological relevance of PIG-A mutations in PNH, aplastic anemia and healthy controls.

Complement in Lupus Nephritis: The Good, the Bad, and the Unknown

The complement system consists of 3 pathways and more than 30 proteins, including those with biological activity that directly or indirectly mediate the effects of this system, plus a set of regulatory proteins necessary to prevent injudicious complement activation on host tissue. The role for complement in the pathogenesis of systemic lupus erythematosus (SLE) is paradoxic. On one hand, the complement system appears to have protective features in that hereditary homozygous deficiencies of classic pathway components are associated with an increased risk for SLE. On the other hand, immune complex-mediated activation of complement in affected tissues is clearly evident in both experimental and human SLE along with pathologic features that are logical consequences of complement activation. By using accurate mouse models of SLE, we have gained remarkable insights into pathogenic features likely relevant to the human disease, and the ability to test potential therapies, some of which have made it to standard clinical use. Studies in genetically altered mice and using recombinant protein inhibitors of complement have confirmed what was believed but unproven-early complement proteins C1q and C4 are protective whereas complement activation later in the pathways is proinflammatory and deleterious. Two complement inhibitors, soluble complement receptor 1 (TP10, Avant Immunotherapeutics, Needham, MA) and a monoclonal anti-C5 antibody (Eculizumab, Alexion Pharmaceuticals, Inc., Cheshire, CT) have been shown to inhibit complement safely and now are being investigated in a variety of clinical conditions. Although these and others earlier in their clinical development hold promise to be used therapeutically in lupus nephritis, this optimism must be tempered by the fact that the clinical trials to prove this remain fraught with obstacles.

New insights into paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is an uncommon intravascular hemolytic anemia that results from the clonal expansion of hematopoietic stem cells harboring somatic mutations in an X-linked gene, termed PIG-A. PIG-A mutations block glycosylphosphatidylinositol (GPI) anchor biosynthesis, resulting in a deficiency or absence of all GPI-anchored proteins on the cell surface. CD55 and CD59 are GPI-anchored complement regulatory proteins. Their absence on PNH red cells is responsible for the complement-mediated intravascular hemolysis. Intravascular hemolysis leads to release of free hemoglobin, which contributes to many of the clinical manifestations of PNH including fatigue, pain, esophageal spasm, erectile dysfunction and possibly thrombosis. Interestingly, rare PIG-A mutations can be found in virtually all healthy control subjects, leading to speculation that PIG-A mutations in hematopoietic stem cells are common benign events. However, negative selection of PIG-A mutant colony-forming cells with proaerolysin, a toxin that targets GPI-anchored proteins, reveals that most of these mutations are not derived from stem cells. Recently, a humanized monoclonal antibody directed against the terminal complement protein C5 has been shown to reduce hemolysis and greatly improve symptoms and quality of life for PNH patients.

Early emergence of PNH-like T cells after allogeneic stem cell transplants utilising CAMPATH-1H for T cell depletion

CAMPATH-1H (C-1H) is widely used in vivo and / or in vitro for T cell depletion in hematopoietic SCT. This humanised monoclonal antibody is specific for CD52, a marker coexpressed on the majority of human lymphocytes with CD48 and other glycosylphosphatidyl-inositol (GPI) anchored proteins. We detected CD52 / CD48 dual expression on >99% of CD3(+) lymphocytes from normal individuals and all 15 post-SCT patients whose transplants did not utilise C-1H. By contrast, 23 / 26 patients with transplants involving C-1H (in vivo, in vitro or both) exhibited populations lacking CD52 expression that accounted for 49.7% (4.2-86.2%) of the CD3+ lymphocytes (median and range) in samples evaluated at a median of 2 months post-SCT. Most CD52- cells also lacked CD48 expression. These GPI- T cells were of either donor or mixed donor / recipient origin. They were predominant in the early months after SCT at times of profound lymphopenia and inversely correlated with the recovery of the absolute lymphocyte count (r= - 0.663, P<0.0001). The presence of CD52- cells has been correlated previously with clinical outcome after CAMPATH therapy for both malignant and nonmalignant diseases.

Contrasting roles of complement activation and its regulation in membranous nephropathy

The complement system is involved in defense against microorganisms, the processing of immune complexes and apoptotic debris, and the development of an appropriate immune response. Along with these physiologic effects, complement activation has the potential to result in tissue pathology. To limit this, various complement regulatory proteins (CRP) are present on host cells, including the glomerular podocyte. Experimental data from the Heymann nephritis (HN) rat model of human membranous nephropathy (MN) have shown that IgG antibodies in subepithelial immune deposits initiate complement activation and C5b-9-mediated damage of the overlying podocyte. Although IgG can activate the classical pathway, there also is evidence that alternative pathway activation occurs in MN, which could occur because of absent, dysfunctional, or inhibited podocyte CRP. Related to this are experimental data in HN showing the presence of antibodies that bind and inhibit podocyte CRP; although such antibodies have not been documented in human MN, a decrease in CR1 quantity on the podocyte has been observed. A s a result of a relative lack of CRP and the exposure of activating complement proteins to tubular cells, alternative complement pathway activation and C5b-9-mediated tubular injury can occur in MN and other proteinuric diseases. Overall, in a disease such as MN, the balance between complement regulation and activation is tipped toward its being activated. Therefore, a number of therapeutic approaches have been developed to counteract this, including recombinant forms of endogenous CRP and complement-inhibitory monoclonal antibodies. There is good reason to be optimistic that approaches to block complement activation will become viable therapy for human MN in the future.

PIG-A mutations in normal hematopoiesis

Paroxysmal nocturnal hemoglobinuria (PNH) is caused by phosphatidylinositol glycan-class A (PIG-A) mutations in hematopoietic stem cells (HSCs). PIG-A mutations have been found in granulocytes from most healthy individuals, suggesting that these spontaneous PIG-A mutations are important in the pathogenesis of PNH. It remains unclear if these PIG-A mutations have relevance to those found in PNH. We isolated CD34+ progenitors from 4 patients with PNH and 27 controls. The frequency of PIG-A mutant progenitors was determined by assaying for colony-forming cells (CFCs) in methylcellulose containing toxic doses of aerolysin (1 x 10(-9) M). Glycosylphosphatidylinositol (GPI)-anchored proteins serve as receptors for aerolysin; thus, PNH cells are resistant to aerolysin. The frequency of aerolysin resistant CFC was 14.7 +/- 4.0 x 10(-6) in the bone marrow of healthy donors and was 57.0 +/- 6.7 x 10(-6) from mobilized peripheral blood. DNA was extracted from individual day-14 aerolysin-resistant CFCs and the PIG-A gene was sequenced to determine clonality. Aerolysin-resistant CFCs from patients with PNH exhibited clonal PIG-A mutations. In contrast, PIG-A mutations in the CFCs from controls were polyclonal, and did not involve T cells. Our data confirm the finding that PIG-A mutations are relatively common in normal hematopoiesis; however, the finding suggests that these mutations occur in differentiated progenitors rather than HSCs.

Mean fluorescence intensity rate is a useful marker in the detection of paroxysmal nocturnal hemoglobinuria clones

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired disorder of the pluripotent stem cell resulting from the somatic mutation of the X-linked

Paroxysmal nocturnal hemoglobinuria in a girl with hemolysis and "hematuria"

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare disorder of unknown frequency. In its classic form, PNH is characterized by hemolysis accompanied by nocturnal hemoglobinuria. The clinical course is unpredictable and may vary from severe hemolysis and recurrent venous thrombosis to latent periods with milder symptoms. We report a 15-year-old girl with hemolytic episodes, abdominal pain, and passage of dark urine. Hemoglobinuria was demonstrated by a "blood"-positive dipstick test in the absence of red blood cells in the urinary sediment. The diagnosis of PNH was confirmed by flow cytometry.

Lymphoid transformation in a CML patient in complete cytogenetic remission following treatment with imatinib

We describe here a patient with Philadelphia (Ph) chromosome-positive chronic myeloid leukemia who achieved a complete cytogenetic response following treatment with imatinib and then progressed abruptly to lymphoid blastic transformation. The sequence of events suggests that at least in some cases patients who respond well to imatinib may still harbor residual leukemia progenitor or 'stem' cells that are susceptible to acquisition of molecular events that underlie progression to advanced phase disease. The case highlights the need for molecular monitoring of responders and the need to develop strategies for reducing to a minimum or totally eradicating leukemia cells.

Hematopoietic stem cells in aplastic anemia

Profound cytopenia involving all blood lineages, a hallmark of aplastic anemia (AA), can result in devastating morbidity and high mortality. Although various etiologies and distinct pathophysiologic mechanisms may be involved, a profound defect in the stem cell compartment is a unifying feature in most patients with AA. As a stem cell disease, AA is very instructive and provides insights into the function and quantity of normal hematopoietic stem cells and their ability to regenerate. Pathophysiologically, understanding of AA may reveal mechanisms as to the evolution of other related bone marrow failure syndromes such as paroxysmal nocturnal hemoglobinuria and myelodysplasia-clonal diseases of hematopoiesis associated with defective stem cells. Conversely, constitutional forms of AA occurring in association with Fanconi anemia and dyskeratosis congenita demonstrate the role of specific genes and pathways in the dysfunction of the stem cells leading to the failure of the stem cell compartment. The acquired mechanisms resulting in depletion of stem cells in AA may involve fundamental pathways such as apoptosis and senescence as well as exhaustion of proliferative capacity or excessive differentiation. Inherent in the paucity of the bone marrow in AA, the study of the stem cells in AA has been very difficult due to their natural rarity and disease-specific contraction of the stem cell pool. Despite these scientific challenges, laboratory studies and systematic clinical observation provide valuable information of significance beyond its specific application to AA.

Haemorrhagic bullae in a case of paroxysmal nocturnal haemoglobinuria

Paroxysmal nocturnal haemoglobinuria is a clonal stem cell disorder manifesting as haemolysis, bone marrow failure and thrombosis. We report a rare cutaneous manifestation on the trunk of a 40-year-old patient. Skin biopsy revealed the presence of fibrin thrombi in the capillaries. The eruption responded within days after commencing oral corticosteroids.