Results of a pilot study of isoniazid in patients with erythropoietic protoporphyria.

Erythropoietic protoporphyria (EPP), the most common porphyria of childhood and the third most common porphyria of adulthood, is characterized clinically by painful, non-blistering cutaneous photosensitivity. Two distinct inheritance patterns involving mutations affecting genes that encode enzymes of the heme biosynthetic pathway underlie the clinical phenotype. Aminolevulinic acid synthase 2 (ALAS2), the rate limiting enzyme of the heme pathway in the erythron, is a therapeutic target in EPP because inhibiting enzyme function would reduce downstream production of protoporphyrin IX (PPIX), preventing accumulation of the toxic molecule and thereby ameliorating symptoms. Isoniazid (INH) is widely used for treatment of latent and active M. tuberculosis (TB). Sideroblastic anemia is observed in some patients taking INH, and studies have shown that this process is a consequence of inhibition of ALAS2 by INH. Based on these observations, we postulated that INH might have therapeutic activity in patients with EPP. We challenged this hypothesis in a murine model of EPP and showed that, after 4 weeks of treatment with INH, both plasma PPIX and hepatic PPIX were significantly reduced. Next, we tested the effect of INH on patients with EPP. After eight weeks, no significant difference in plasma or red cell PPIX was observed among the 15 patients enrolled in the study. These results demonstrate that while INH can lower PPIX in an animal model of EPP, the standard dose used to treat TB is insufficient to affect levels in humans.

Dynamic dosing of romiplostim in patients with immune thrombocytopenia purpura: Two case reports.

Romiplostim is a thrombopoietin receptor agonist approved for the treatment of immune thrombocytopenia purpura. When following FDA-approved romiplostim prescribing recommendations to withhold treatment for platelet counts above 400k/µL, some patients exhibit a precipitous decline in their platelet count potentially causing patient harm. We present two cases where stable platelet counts were achieved only through persistent weekly dosing of romiplostim despite platelet counts above 400k/µL on the day of administration. Therefore, continuous weekly dosing of romiplostim despite platelet count being above 400k/µL combined with twice weekly vigilant monitoring is an alternative method of romiplostim dosing that mitigates severe fluctuations in platelets. We also discuss important details, postulated mechanisms, and evidence-based mitigation strategies.

Cirrhosis in Hemochromatosis: Independent Risk Factors in 368 HFE p.C282Y Homozygotes.

INTRODUCTION AND AIM: We sought to identify independent risk factors for cirrhosis in HFE p.C282Y homozygotes in a cross-sectional study. MATERIAL AND METHODS: We evaluated 368 p.C282Y homozygotes who underwent liver biopsy and compared characteristics of those with and without cirrhosis. We performed multivariable logistic regression on cirrhosis with: age; sex; race/ethnicity; diabetes; blood pints/units donated voluntarily; erythrocyte pints/units received; iron supplement use; alcohol intake, g/d; body mass index, kg/m2; swollen/tender 2nd/3rd metacarpophalangeal joints; elevated alanine aminotransferase; elevated aspartate aminotransferase; steatosis/fatty liver; iron removed by phlebotomy, g; and GNPAT p.D519G positivity. RESULTS: Mean age of 368 participants (73.6% men) was 47 ± 13 (standard deviation) y. Cirrhosis was diagnosed in 86 participants (23.4%). Participants with cirrhosis had significantly greater mean age, proportion of men, diabetes prevalence, mean daily alcohol intake, prevalence of swollen/ tender 2nd/3rd metacarpophalangeal joints, mean serum ferritin, elevated alanine aminotransferase, elevated aspartate aminotransferase, and mean iron removed; and significantly fewer mean blood pints/units donated. GNPAT p.D519G positivity was detected in 82 of 188 participants (43.6%). In a multivariable model for cirrhosis, there were four significant positive associations: age (10-y intervals) (odds ratio 2.2 [95% confidence interval 1.5, 3.3]); diabetes (3.3; [1.1, 9.7]); alcohol intake (14 g alcohol drinks/d) (1.5 [1.2, 1.8]); and iron removed, g (1.3 [1.2, 1.4]). There was no statistical evidence of two-way interactions between these variables. CONCLUSION: In conclusion, cirrhosis in HFE p.C282Y homozygotes is significantly associated with age, diabetes, daily alcohol intake, and iron removed by phlebotomy, taking into account the effect of other variables.

GNPAT p.D519G is independently associated with markedly increased iron stores in HFE p.C282Y homozygotes.

BACKGROUND: GNPAT p.D519G positivity is significantly increased in HFE p.C282Y homozygotes with markedly increased iron stores. We sought to determine associations of p.D519G and iron-related variables with iron stores in p.C282Y homozygotes. METHODS: We defined markedly increased iron stores as serum ferritin >2247pmol/L (>1000µg/L) and either hepatic iron >236µmol/g dry weight or iron >10g by induction phlebotomy (men and women). We defined normal or mildly elevated iron stores as serum ferritin <674.1pmol/L (<300µg/L) or either age≥40y with iron ≤2.5g iron by induction phlebotomy or age≥50y with ≤3.0g iron by induction phlebotomy (men only). We compared participant subgroups using univariate methods. Using multivariable logistic regression, we evaluated associations of markedly increased iron stores with these variables: age; iron supplement use (dichotomous); whole blood units donated; erythrocyte units received as transfusion; daily alcohol consumption, g; and p.D519G positivity (heterozygosity or homozygosity). RESULTS: The mean age of 56 participants (94.6% men) was 55±10 (SD) y; 41 had markedly increased iron stores. Prevalences of swollen/tender 2nd/3rd metacarpophalangeal joints and elevated aspartate or alanine aminotransferase were significantly greater in participants with markedly increased iron stores. Only participants with markedly increased iron stores had cirrhosis. In multivariable analyses, p.D519G positivity was the only exposure variable significantly associated with markedly increased iron stores (odds ratio 9.9, 95% CI [1.6, 60.3], p=0.0126). CONCLUSIONS: GNPAT p.D519G is strongly associated with markedly increased iron stores in p.C282Y homozygotes after correction for age, iron-related variables, and alcohol consumption.

Exome sequencing for molecular characterization of non-HFE hereditary hemochromatosis.

Diagnostic genetic testing for hereditary hemochromatosis is readily available for clinically relevant HFE variants (i.e., those that generate the C282Y, H63D and S65C HFE polymorphisms); however, genetic testing for other known causes of iron overload, including mutations affecting genes encoding hemojuvelin, transferrin receptor 2, HAMP, and ferroportin is not. As an alternative to conventional genetic testing we propose diagnostic use of whole exome sequencing for characterization of non-HFE hemochromatosis. To illustrate the effectiveness of whole exome sequencing as a diagnostic tool, we present the case of an 18-year-old female with a probable case of juvenile hemochromatosis, who was referred for specialty care after testing negative for commonly occurring HFE variants. Whole exome sequencing offered complete coverage of target genes and is a fast, cost effective diagnostic tool for characterization of non-HFE hemochromatosis.

Methylation of AR locus does not always reflect X chromosome inactivation state.

Clonality can be established by a lack of mosaicism in a female because of random inactivation of either the maternal or paternal X chromosome early in embryogenesis. The methylation status of CpG sites close to the trinucleotide repeats in exon 1 of the human androgen receptor (AR) X chromosome gene assay (HUMARA) has been used to determine clonality. This HUMARA at times indicated clonal hematopoiesis in healthy elderly women, thus precluding its applicability. We used a clonality assay based on quantitative expression of polymorphic X chromosome genes (qTCA) and found no evidence of clonal hematopoiesis in healthy nonanemic elderly persons. We found instances of discordance between HUMARA results and those obtained by pyrosequencing and qTCA methods, as well as by directly quantifying AR gene expression. To determine the basis of this discrepancy we examined the methylation pattern of the AR locus subject to HUMARA. Notably, we found the extent of DNA methylation to be highly variable at the AR gene in granulocytes of persons with discordant results and also in erythroid burst-forming unit colonies but not in those with clonal hematopoiesis. These data provide the molecular basis of incomplete correlation with the pattern of DNA methylation of this X chromosome AR gene locus.

Paroxysmal nocturnal hemoglobinuria.

PURPOSE OF REVIEW: The aim is to report on recent observations related to the natural history of paroxysmal nocturnal hemoglobinuria (PNH) and to review new therapeutic strategies for controlling the hemolysis of PNH. RECENT FINDINGS: This review focuses on studies designed to characterize the long-term outcome of patients with PNH treated with eculizumab and to define the relationship between PNH and bone marrow failure syndromes. New therapeutic strategies aimed at controlling extravascular as well as intravascular hemolysis are also examined. SUMMARY: Long-term safety and efficacy of eculizumab was observed in a large group of patients. Survival for the group was not different from that of a sex-matched and age-matched control group from the general population. Thrombotic complications were rare and deaths due to PNH or complications of therapy were not observed. These studies suggest that patients with clinical PNH who are treated with eculizumab have a benign clinical course. Patients with bone marrow failure who have PNH cells detected by high-sensitivity flow cytometry have aplastic anemia or low-risk myelodysplastic syndrome. For patients with a percentage of PNH cells that is below the threshold for producing laboratory evidence of hemolysis (subclinical PNH), expansion of the clone to a size sufficient to produce clinical PNH is not observed. Approximately 50% of patients with bone marrow failure who have clinical evidence of PNH at presentation will require PNH-specific therapy. Novel reagents that target the alternative pathway of complement C3 convertase are being developed with a goal of inhibiting both the extravascular and the intravascular hemolysis of PNH.

A novel approach to preventing the hemolysis of paroxysmal nocturnal hemoglobinuria: both complement-mediated cytolysis and C3 deposition are blocked by a monoclonal antibody specific for the alternative pathway of complement.

The clinical hallmark of paroxysmal nocturnal hemoglobinuria (PNH) is chronic intravascular hemolysis that is a consequence of unregulated activation of the alternative pathway of complement (APC). Intravascular hemolysis can be inhibited in patients by treatment with eculizumab, a monoclonal antibody that binds complement C5 thereby preventing formation of the cytolytic membrane attack complex of complement. However, in essentially all patients treated with eculizumab, persistent anemia, reticulocytosis, and biochemical evidence of hemolysis are observed; and in a significant proportion, their PNH erythrocytes become opsonized with complement C3. These observations suggest that PNH patients treated with eculizumab are left with clinically significant immune-mediated hemolytic anemia because the antibody does not block APC activation. With a goal of improving PNH therapy, we characterized the activity of anti-C3b/iC3b monoclonal antibody 3E7 in an in vitro model of APC-mediated hemolysis. We show that 3E7 and its chimeric-deimmunized derivative H17 block both hemolysis and C3 deposition on PNH erythrocytes. The antibody is specific for the APC C3/C5 convertase because classical pathway-mediated hemolysis is unaffected by 3E7/H17. These findings suggest an approach to PNH treatment in which both intravascular and extravascular hemolysis can be inhibited while preserving important immune functions of the classical pathway of complement.

ABCB6 polymorphisms are not overly represented in patients with porphyria.

The Mendelian inheritance pattern of acute intermittent porphyria, hereditary coproporphyria, and variegate porphyria is autosomal dominant, but the clinical phenotype is heterogeneous. Within the general population, penetrance is low, but among first-degree relatives of a symptomatic proband, penetrance is higher. These observations suggest that genetic factors, in addition to mutation of the specific enzyme of the biosynthetic pathway of heme, contribute to the clinical phenotype. Recent studies by others suggested that the genotype of the transporter protein ABCB6 contribute to the porphyria phenotype. Identifying the molecule(s) that are transported by ABCB6 has been problematic and has led to uncertainty with respect to how or if variants/mutants contribute to phenotypic heterogeneity. Knockout mouse models of Abcb6 have not provided a direction for investigation as homozygous knockout animals do not have a discrete phenotype. To address the proposed link between ABC6 genotype and porphyria phenotype, a large cohort of patients with acute hepatic porphyria and erythropoietic protoporphyria was analyzed. Our studies showed that ABCB6 genotype did not correlate with disease severity. Therefore, genotyping of ABCB6 in patients with acute hepatic porphyria and erythropoietic protoporphyria is not warranted.

How Do Red Blood Cells Die?

Normal human red blood cells have an average life span of about 120 days in the circulation after which they are engulfed by macrophages. This is an extremely efficient process as macrophages phagocytose about 5 million erythrocytes every second without any significant release of hemoglobin in the circulation. Despite large number of investigations, the precise molecular mechanism by which macrophages recognize senescent red blood cells for clearance remains elusive. Red cells undergo several physicochemical changes as they age in the circulation. Several of these changes have been proposed as a recognition tag for macrophages. Most prevalent hypotheses for red cell clearance mechanism(s) are expression of neoantigens on red cell surface, exposure phosphatidylserine and decreased deformability. While there is some correlation between these changes with aging their causal role for red cell clearance has not been established. Despite plethora of investigations, we still have incomplete understanding of the molecular details of red cell clearance. In this review, we have reviewed the recent data on clearance of senescent red cells. We anticipate recent progresses in in vivo red cell labeling and the explosion of modern proteomic techniques will, in near future, facilitate our understanding of red cell senescence and their destruction.

Anticoagulation management post-transjugular intrahepatic portosystemic shunt in portal hypertension associated with myeloproliferative neoplasms.

Portal hypertension (pHTN) complicates myeloproliferative neoplasms (MPNs), and usually occurs due to Budd-Chiari syndrome or splanchnic vein thrombosis. Current management modalities for MPN-associated pHTN include anticoagulation, transjugular intrahepatic portosystemic shunt (TIPS), and orthotopic liver transplant. Data on the thrombotic and bleeding outcomes of this practice is of poor quality, and whether direct oral anticoagulants (DOACs) are effective in this setting is unknown. We describe failure of DOACs to prevent post-TIPS complications in two case reports of patients with MPN-associated pHTN and review the associated literature. We conducted a comprehensive search in Embase (embase.com), Scopus (scopus.org), and PubMed for existing data on MPN-associated pHTN post-TIPS procedure. Four studies (n = 251) of patients with pHTN post-TIPS were eligible (MPN, n = 143). A review of the literature suggests that patients with MPN-associated pHTN may be at higher risk for post-TIPS complications including stent thrombosis and stenosis, compared with other causes of thrombotic pHTN. DOAC use has not been studied in this setting. While further studies to guide optimal management of MPN-associated pHTN post-TIPS are needed, available evidence suggests that life-long anticoagulation is warranted. DOACs should not be considered standard of care because of lack of evidence of efficacy.

The pathophysiology of paroxysmal nocturnal hemoglobinuria.

The molecular basis of PNH is known. Somatic mutation of the X-chromosome gene PIGA accounts for deficiency of glycosyl phosphatidylinositol-anchored proteins (GPI-AP) on affected hematopoietic stem cells and their progeny. However, neither mutant PIGA nor the consequent deficiency of GPI-AP provides a direct explanation for the clonal outgrowth of the mutant stem cells. Therefore, PNH differs from malignant myelopathies in which clonal expansion is directly attributable to a specific, monogenetic event (e.g., t(9;22) in CML) that bestows a growth/survival advantage upon the affected cell. Multiple, discrete PIGA mutant clones are present in many patients, suggesting that a selection pressure that favors the PNH phenotype (i.e., GPI-AP deficiency) was applied to the bone marrow. The nature of this putative selection pressure, however, is speculative, as is the basis of clonal expansion. In many patients, the majority of hematopoiesis is derived from PIGA mutant stem cells. Yet clonal expansion is limited (nonmalignant), and the contribution of the mutant clones to hematopoiesis may remain stable for decades. Understanding the basis of clonal selection and expansion will not only delineate further the pathophysiology of PNH but also provide new insights into stem cell biology and suggest novel therapeutic strategies for enhancing marrow function.

Update on the diagnosis and management of paroxysmal nocturnal hemoglobinuria.

Once suspected, the diagnosis of paroxysmal nocturnal hemoglobinuria (PNH) is straightforward when flow cytometric analysis of the peripheral blood reveals a population of glycosyl phosphatidylinositol anchor protein-deficient cells. But PNH is clinically heterogeneous, with some patients having a disease process characterized by florid intravascular, complement-mediated hemolysis, whereas in others, bone marrow failure dominates the clinical picture with modest or even no evidence of hemolysis observed. The clinical heterogeneity is due to the close, though incompletely understood, relationship between PNH and immune-mediated bone marrow failure, and that PNH is an acquired, nonmalignant clonal disease of the hematopoietic stem cells. Bone marrow failure complicates management of PNH because compromised erythropoiesis contributes, to a greater or lesser degree, to the anemia; in addition, the extent to which the mutant stem cell clone expands in an individual patient determines the magnitude of the hemolytic component of the disease. An understanding of the unique pathobiology of PNH in relationship both to complement physiology and immune-mediated bone marrow failure provides the basis for a systematic approach to management.

The D519G Polymorphism of Glyceronephosphate O-Acyltransferase Is a Risk Factor for Familial Porphyria Cutanea Tarda.

Both familial and sporadic porphyria cutanea tarda (PCT) are iron dependent diseases. Symptoms of PCT resolve when iron stores are depleted by phlebotomy, and a sequence variant of HFE (C282Y, c.843G>A, rs1800562) that enhances iron aborption by reducing hepcidin expression is a risk factor for PCT. Recently, a polymorphic variant (D519G, c.1556A>G, rs11558492) of glyceronephosphate O-acyltransferase (GNPAT) was shown to be enriched in male patients with type I hereditary hemochromatosis (HFE C282Y homozygotes) who presented with a high iron phenotype, suggesting that GNPAT D519G, like HFE C282Y, is a modifier of iron homeostasis that favors iron absorption. To challenge this hypothesis, we investigated the frequency of GNPAT D519G in patients with both familial and sporadic PCT. Patients were screened for GNPAT D519G and allelic variants of HFE (both C282Y and H63D). Nucleotide sequencing of uroporphyrinogen decarboxylase (URO-D) identified mutant alleles. Patients with low erythrocyte URO-D activity or a damaging URO-D variant were classified as familial PCT (fPCT) and those with wild-type URO-D were classified as sporadic PCT (sPCT). GNPAT D519G was significantly enriched in the fPCT patient population (p = 0.0014) but not in the sPCT population (p = 0.4477). Both HFE C282Y and H63D (c.187C>G, rs1799945) were enriched in both PCT patient populations (p<0.0001) but showed no greater association with fPCT than with sPCT. CONCLUSION: GNPAT D519G is a risk factor for fPCT, but not for sPCT.

Rare event counting of CD59- red cells in human blood: A 47-month experience using PNH consensus guidelines for WBC and RBC testing in a reference lab.

INTRODUCTION: Paroxysmal nocturnal hemoglobinuria (PNH) is a rare acquired disorder characterized by increased complement-mediated lysis of erythrocytes (RBCs) because of low/absent glycophosphatidylinositol (GPI) anchors of numerous cell surface proteins. METHODS: Rare event analysis was applied to 120 million RBCs (12 normal individuals) and 102 million RBCs (102 normal individuals) to establish a reference range and verify a methodology for rare event analysis. Patient PNH testing (n = 10,984) was performed over 47 months using the 2010 consensus guidelines with CD59-PE and glycophorin A-FITC for RBCs and FLAER-Alexa 488, CD33-PerCP-Cy5.5, CD15-APC, CD14-APC-Cy7, and CD24-PE for WBCs. RESULTS: The distribution of CD59- RBCs in the normal population was asymmetric with a mean of 5.9, median between 3 and 4, and mode of 2 per million RBCs. The normal range of CD59- RBCs was 0-17/million RBCs. A natural cutoff of 2.5% of the peak expression of CD59 delineates CD59+ from CD59- populations. The incidence of GPI- samples received by the laboratory was 6-7% without correlation to age (P = 0.35) or sex (P = 0.45). The percentage of GPI- neutrophils and monocytes were strongly correlated (R(2) = 0.96) and usually greater than the percentage of GPI- RBCs. CONCLUSION: PNH RBC testing is a good example of rare event analysis applied to clinical cytometry­only 2.5 min are required to collect 1 million RBCs. With an established normal range of CD59- RBCs, the correlation between total cell count and sensitivity for detecting an abnormal population can be calculated using Poisson statistics.

Management issues in paroxysmal nocturnal hemoglobinuria.

Paroxysmal nocturnal hemoglobinuria (PNH) arises in the setting of bone marrow injury. Thus, management decisions must take into account whether symptoms are a consequence of the underlying marrow failure or of the expansion of the clone of the PIG-A mutant hematopoietic cells. The primary clinical manifestations of PNH are intravascular hemolysis and thrombophilia. Currently available options for treatment of the hemolysis of PNH are unsatisfactory, but the recent development of specific inhibitors of complement for use in treating human disease should make possible effective management of this pathology. The fundamental basis of the thrombophilia of PNH has not been elucidated. Currently, empiric anticoagulant therapy is the foundation for treating the thromboembolic complications of PNH. The role of warfarin prophylaxis, however, remains an area of active debate. Pregnancy in a patient with PNH presents special concerns about fetal/maternal well-being because of the high potential for thromboembolic complications. Bone marrow transplantation can be considered curative, but the decision to recommend this treatment must take into account factors related both to PNH and to comorbid conditions. Refining the technology for both gene therapy (by transducing stem cells with a functional PIG-A gene) and autotransplantation (by using stem cells selected for the expression of glycosyl phosphatidylinositol-anchored proteins) remain challenges for the future.