Survival of a Jehovah's Witness with thrombotic thrombocytopenic purpura without using plasma: A case report and review of the literature.

Acquired thrombotic thrombocytopenic purpura (aTTP) is a serious disorder with arteriolar and capillary thrombosis for which the treatment usually requires plasma exchange with plasma as the replacement fluid. Management of patients who do not accept blood products is a serious challenge. We present the case of a Jehovah's Witness patient who achieved clinical response after treatment with plasma exchange using human albumin solution as the replacing fluid, high dose corticosteroids, and rituximab. The patient also received ADAMTS13 containing plasma cryoprecipitate and von Willebrand factor VIII concentrates. She had an exacerbation of her TTP in less than 3 weeks. She was treated with further plasma exchange with human albumin solution as the replacement fluid, high dose steroids, and rituximab. Bortezomib and N-acetylcysteine were added. The patient eventually improved clinically and achieved remission that is ongoing for more than 7 months. A review of the literature shows that all five previously reported cases of aTTP in Jehovah's Witnesses survived although none received plasma. Two were not even treated with plasma exchange. The experience of this case and those in the literature demonstrates that remission of aTTP may be achieved without using plasma or plasma exchange.

Autoimmune thrombotic microangiopathy: advances in pathogenesis, diagnosis, and management.

Thrombotic microangiopathy, or the syndrome of thrombocytopenia and hemolysis with schistocytes on blood smears, has been a subject of uncertainty and intense controversy. The pathogenesis of thrombotic microangiopathy was unknown and no classification of thrombotic thrombocytopenic purpura and hemolytic uremic syndrome was satisfactory. In recent years, a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS-13) deficiency and defective complement regulation have been identified as the two major causes of noninfectious thrombotic microangiopathy. It is now possible to classify thrombotic microangiopathy pathogenetically rather than clinically, and a distinction between diseases and clinical syndromes is emerging. This pathogenesis-based disease classification requires new diagnostic approaches and provides a framework for rational therapeutic designs. This review discusses the new concepts in the pathogenesis, diagnosis, and management of thrombotic microangiopathy, with particular emphasis on the autoimmune causes of ADAMTS-13 deficiency and defective complement regulation.

N-Glycans of ADAMTS13 modulate its secretion and von Willebrand factor cleaving activity.

Severe deficiency of ADAMTS13, a plasma metalloprotease, leads to thrombotic thrombocytopenic purpura. ADAMTS13 contains 10 putative N-glycosylation sites in or near its metalloprotease sequence, spacer region, thrombospondin type 1 repeat no. 4 (TSR no. 4), and CUB domains. Tunicamycin treatment markedly decreased the secretion of ADAMTS13 into the culture medium of transfected cells. Nevertheless, the protease was efficiently secreted from N-acetylglucosaminyltransferase I-deficient Lec1 Chinese hamster ovary cells, indicating that N-glycosylation in the endoplasmic reticulum, but not the conversion of oligomannose to complex N-glycans in the Golgi complex, is important for secretion. However, ADAMTS13 with oligomannose N-glycans cleaved its substrate, von Willebrand factor (VWF) multimers, less effectively, with a higher K(m) but similar k(cat) value. In mutagenesis analysis, decreased secretion and VWF cleaving activity was observed with the N146Q and N828Q mutants, while decreased secretion only was observed with the N552Q mutant of ADAMTS13. Enzymatic removal of N-glycans from ADAMTS13 did not affect its VWF cleaving activity. Thus, N-glycosylation is necessary for efficient secretion of ADAMTS13, while conversion of the N-glycans from oligomannose to complex type in the Golgi complex enhances the proteolytic activity of the protease toward VWF multimers. After its secretion, ADAMTS13 does not require N-glycans for its VWF cleaving activity.

Excessive activation of the complement system in atypical hemolytic uremic syndrome: is it ready for prime time?

Complement factor I (CFI) mutations are implicated in the pathogenesis of atypical hemolytic uremic syndrome (aHUS). Nevertheless, there is evidence that CFI deficiency is a weak effector of aHUS. Bienaime et al. report that homozygous deletion of CFHR-1 in the RCA gene cluster of chromosome 1q is a major risk factor for poor outcome for patients with CFI mutations. The basic and clinical implications of the findings are further elaborated here.

Myocardial Infarction with Limb Arterial and Venous Thrombosis in a Patient with Enoxaparin-Induced Thrombocytopenia.

BACKGROUND Heparin, often used as an anticoagulant, acts by binding to antithrombin III. Indeed, heparin binds to a variety of proteins other than antithrombin III. Among them, platelet factor 4 can bind and neutralize the anticoagulant activity of heparin. Upon binding with heparin, platelet factor 4 undergoes a conformational change and expresses immunogenic neo-epitopes that induce the generation of antibodies of the platelet factor 4 heparin complex. This immune reaction may lead to thrombocytopenia and venous, arterial, or microvascular thrombosis. However, the risk of such complications is quite variable, as it is affected not only by the source and dose of heparin and the clinical condition (e.g., cardiovascular surgery and orthopedic surgery) of the patient, but also the molecular size of the heparin formulation. Venous, arterial, and small-vessel thrombosis can lead to leg swelling, pulmonary embolism, stroke, skin necrosis, or gangrene requiring limb amputation or intestinal resection. Myocardial infarction due to coronary thrombosis also occurs, although it is less common and can be readily recognized. CASE REPORT Heparin-induced thrombocytopenia (HIT) is a potentially life-threatening complication of heparin therapy. We report the case of a 67-year-old woman who developed ST-segment elevation myocardial infarction and thrombocytopenia within 10 days of prophylactic enoxaparin therapy after undergoing bilateral total knee replacement surgery. She also had peripheral arterial and venous thrombosis. With thrombolysis and argatroban anticoagulation therapy, she recovered without residual sequelae. CONCLUSIONS Thrombocytopenia with coronary and other vascular thrombosis is a potentially serious complication of heparin therapy. A trend of decreased platelet count, decreased platelet count by 30% or more, and/or occurrence of any type of thrombosis should raise the suspicion of HIT. This case demonstrates that early recognition and prompt treatment of HIT can be life-saving.

Mechanisms of microvascular thrombosis in thrombotic thrombocytopenic purpura.

Recent studies have demonstrated that thrombotic thrombocytopenic purpura (TTP), a serious thrombotic disorder affecting the arterioles and capillaries of multiple organs, is caused by a profound deficiency in the von Willebrand factor cleaving metalloprotease, ADAMTS13. ADAMTS13, a 190-kD plasma protease originating primarily in hepatic stellate cells, prevents microvascular thrombosis by cleaving von Willebrand factor when the substrate is conformationally unfolded by high levels of shear stress in the circulation. Deficiency of ADAMTS13, due to genetic mutations or inhibitory autoantibodies, leads to accumulation of superactive forms of vWF, resulting in vWF-platelet aggregation and microvascular thrombosis. Analysis of ADAMTS13 has led to the recognition of subclinical TTP and atypical TTP presenting with thrombocytopenia or acute focal neurological deficits without concurrent microangiopathic hemolysis. Infusion of plasma replenishes the missing ADAMTS13 and ameliorates the complications of hereditary TTP. The patients are at risk of both acute and chronic renal failure if they receive inadequate plasma therapy. The more frequent, autoimmune type of TTP requires plasma exchange therapy and perhaps immunomodulatory measures. Current studies focus on the factors affecting the phenotypic severity of TTP and newer approaches to improving the therapies for the patients.

The influence of riboflavin photochemistry on plasma coagulation factors.

UNLABELLED: Studies with riboflavin in the 1960s showed that it could be effective at inactivating pathogens when exposed to light. The principal mode of action is through electron transfer reactions, most importantly in nucleic acids. This suggested that it could act as a photosensitizer useful in the inactivation of pathogens found in blood products. OBJECTIVE: To study the influence of photo-inactivation with riboflavin on the coagulation factors of plasma. METHODS: The photo-inactivation procedure of riboflavin plus light was applied. Fifty isogroup pools of two plasmas were made from 100U of plasma that were derived from whole blood products that had previously been held overnight. Pools were split into two bags. One of them was photo-inactivated, and post inactivation samples were obtained. The second bag was not photo-inactivated and samples were taken. Total protein, fibrinogen, FII, FV, FVII, FVIII, FIX, FX, FXI, FXIII, antithrombin III, PC, PS, alpha-2 antiplasmin and vWF:Ag, the multimeric structure of vWF and ADAMTS-13 were analyzed. RESULTS: In plasma, the proteins most sensitive to photo-inactivation were fibrinogen, FXI, FVIII, FV, and FIX (33%, 32%, 30%, 18% and 18% loss, respectively). Coagulation inhibitors, PS, antithrombin III and PC showed little decrease (all 2%). Retention of vWF and ADAMTS-13 were 99% and 88%, respectively. CONCLUSIONS: As with other pathogen reduction procedures for plasma products, treatment with riboflavin and UV light resulted in reduction in the activity levels of several pro-coagulant factors. Coagulation inhibitors are well preserved.

Thrombotic Thrombocytopenic Purpura: Beyond Empiricism and Plasma Exchange.

For many years after its first description in 1924, thrombotic thrombocytopenic purpura was an intriguing puzzle for clinicians and researchers, not only for its unique pathology, perplexing changes in von Willebrand factor multimers, and high rate of rapid fatality but also for its dramatic response to plasma infusion or exchange. The discovery of ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 repeats member-13) and its deficiency in patients with thrombotic thrombocytopenic purpura, due to inhibitory autoantibodies or genetic mutations, provides a mechanistic scheme for understanding its pathogenesis. This new knowledge quickly led to the use of rituximab to promote its remission and prevent recurrence. Recombinant ADAMTS13 is also under development to replace plasma infusion as the therapy for hereditary thrombotic thrombocytopenic purpura. Recently, caplacizumab, a bivalent nanobody targeting the glycoprotein 1b binding epitope of von Willebrand factor A1 domain, was approved as an addition to the current regimen of plasma exchange and immunomodulation for adult patients of acquired thrombotic thrombocytopenic purpura. This review discusses how the new treatment may improve patient outcomes and its potential pitfalls.

Atypical Hemolytic Uremic Syndrome: Beyond Hemolysis and Uremia.

Atypical hemolytic uremic syndrome commonly presents with the triad of microangiopathic hemolytic anemia, thrombocytopenia, and renal function impairment without an antecedent hemorrhagic diarrhea. Less known are extrarenal complications due to abnormal vascular permeability, although these are a major cause of morbidity and mortality for the patients. Furthermore, it is increasingly recognized that the disease may present with hypertension or renal function impairment with no or mild thrombocytopenia and microangiopathic hemolytic anemia. Awareness of the full spectrum of atypical hemolytic uremic syndrome may facilitate its diagnosis and treatment before serious complications or death occurs.

Shigatoxin triggers thrombotic thrombocytopenic purpura in genetically susceptible ADAMTS13-deficient mice.

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening illness caused by deficiency of the vWF-cleaving protease ADAMTS13. Here we show that ADAMTS13-deficient mice are viable and exhibit normal survival, although vWF-mediated platelet-endothelial interactions are significantly prolonged. Introduction of the genetic background CASA/Rk (a mouse strain with elevated plasma vWF) resulted in the appearance of spontaneous thrombocytopenia in a subset of ADAMTS13-deficient mice and significantly decreased survival. Challenge of these mice with shigatoxin (derived from bacterial pathogens associated with the related human disease hemolytic uremic syndrome) resulted in a striking syndrome closely resembling human TTP. Surprisingly, no correlation was observed between plasma vWF level and severity of TTP, implying the existence of TTP-modifying genes distinct from vWF. These data suggest that microbe-derived toxins (or possibly other sources of endothelial injury), together with additional genetic susceptibility factors, are required to trigger TTP in the setting of ADAMTS13 deficiency.

Evolution of ADAMTS13 antibodies in a fatal case of thrombotic thrombocytopenic purpura.

In a patient with fatal thrombotic thrombocytopenic purpura, the inhibitory activity of antibodies against ADAMTS13 rapidly escalated to extremely high levels despite daily plasma exchange and corticosteroid therapy. This increase was found to be because of a combination of higher antibody concentration and potency. Furthermore, during her course of the disease, the percentage of IgG(1) antibody progressively decreased whereas that of IgG(2) antibody increased, suggesting Th1-type cytokine response. These changes suggest that the course of TTP may be exacerbated by complex immune reactions. Further characterization of the factors contributing to this exacerbation may have important pathogenetic and therapeutic implications.

Thrombotic thrombocytopenic purpura: a thrombotic disorder caused by ADAMTS13 deficiency.

A serious disorder with characteristic microvascular thrombosis involving the brain and other organs, thrombotic thrombocytopenic purpura (TTP) typically presents with thrombocytopenia, hemolysis with schistocytes on blood smears, and mental changes or seizures. It may progress rapidly to a fatal end if the patient is not treated immediately with plasma. Recent advances have shown that TTP is caused by deficiency of a circulating, von Willebrand factor cleaving metalloprotease, ADAMTS13. This new knowledge will provide clues to improve the diagnosis and management of this intriguing disease.

ADAMTS13-binding IgG are present in patients with thrombotic thrombocytopenic purpura.

Functional assays are commonly used to measure the antibodies of ADAMTS13 found in patients of thrombotic thrombocytopenic purpura (TTP). In this study we used an enzyme-linked immunoassay to analyze the ADAMTS13-binding IgG levels in six groups of individuals: normal, random hospitalized patients, acute TTP, TTP after receiving plasma therapy, TTP in remission, and other types of thrombotic microangiopathy (TMA). The results showed that ADAMTS13-binding IgG levels were elevated in 100% of the acute TTP group, 75% of the TTP group after receiving plasma therapy, and 40% of the remission group. Overall, the ADAMTS13-binding IgG levels correlated with the inhibitory activity levels againstADAMTS13 (r = -0.69, P < 0.0001). The assay also detected elevated IgG binding levels in 5% - 15% of the normal, random, and other TMA control groups. Addition of purified ADAMTS13 protein to the plasma samples suppressed the IgG binding in each of the acute TTP patients, but in none of the non-TTP groups. Serial measurement in a patient that had two exacerbations of TTP within the first three weeks revealed that the ADAMTS13 activity levels remained <0.1 U/ml during this period, and the ADAMTS13-binding IgG remained elevated, suggesting that ADAMTS13 analysis may provide valuable insight to the disease status during the course of therapy. Analysis of ADAMTS13-binding IgG is helpful for the diagnosis and management of TTP.

From Gestational Hypertension and Preeclampsia to Atypical Hemolytic Uremic Syndrome.

BACKGROUND: Preeclampsia is a leading cause of morbidity and mortality during pregnancy. The variability of clinical features suggests that preeclampsia is not a single disease. Atypical hemolytic uremic syndrome, resulting from defective regulation of the alternative complement pathway, is less well known and may be mistaken for preeclampsia. CASE: We describe a woman with atypical hemolytic uremic syndrome who was given the diagnosis of gestational hypertension during her first pregnancy and preeclampsia and hemolysis, elevated liver enzymes, and low platelet count (HELLP) syndrome followed by thrombotic thrombocytopenic purpura and hemolytic uremic syndrome during her second pregnancy, before the correct diagnosis of atypical hemolytic uremic syndrome was recognized in the postpartum period of her third pregnancy. The patient was treated with anticomplement therapy and had a rapid improvement. CONCLUSION: This case illustrates the importance of distinguishing atypical hemolytic uremic syndrome from preeclampsia.

Platelet activation and the formation of the platelet plug: deficiency of ADAMTS13 causes thrombotic thrombocytopenic purpura.

In the circulation, a plasma metalloprotease, ADAMTS13, cleaves von Willebrand factor (vWF) in a shear-dependent manner. This article reviews the role of this cleavage in regulating vWF-platelet interaction and proposes a scheme for understanding how a deficiency of ADAMTS13 results in the development of microthrombi in patients with thrombotic thrombocytopenic purpura.

Von Willebrand factor, ADAMTS13, and thrombotic thrombocytopenic purpura.

Von Willebrand factor (vWF), a glycoprotein critical for supporting platelet adhesion and aggregation at sites of vessel injury, exists in the plasma as a series of multimers. Recent studies have shown that a metalloprotease cleaves endothelial vWF to a series of multimers. A deficiency of the protease activity due to autoimmune IgG inhibitors or genetic mutations is associated with thrombotic thrombocytopenic purpura (TTP). Positional cloning based on kindreds with a genetic deficiency of the protease and amino acid sequencing of the purified protein have identified the protease as a novel member of the ADAMTS (a disintegrin and metalloprotease with thrombospondin type 1 repeat) zinc metalloprotease family located on the long arm of chromosome 9. Mutations of the gene are detected in patients with the congenital form of TTP. These findings support the view that vWF proteolysis is critical in regulating vWF-platelet interaction and set the stage for improving the diagnosis and treatment of thrombotic thrombocytopenic purpura.