The International Hereditary Thrombotic Thrombocytopenic Purpura Registry: key findings at enrollment until 2017

Pregnancy-onset thrombotic thrombocytopenic purpura with nephrotic syndrome: a case report

Pregnancy-onset thrombotic thrombocytopenic purpura (TTP) was reported by many obstetricians and hematologists, but less by nephrologists, and the detailed clinical course of its renal complication is not known. Here, we report a case of a 33-year-old pregnant woman who suffered from pregnancy-onset TTP with nephrotic syndrome which was controlled by the termination of pregnancy. On admission, she had periorbital and lower leg edema at 32 weeks of gestation. Her serum albumin level was 2.8 g/dL and the urine protein/creatinine ratio was 4.1 g/g Cr. Besides those, she had thrombocytopenia, hemolytic anemia, and severe deficiency of A Disintegrin-like and Metalloproteinase with Thrombospondin type 1 motifs 13 (ADAMTS-13) activity. Thus, she was diagnosed with nephrotic syndrome due to pregnancy-onset TTP. A cesarean section was performed without complications for the patient and her baby. Then, all her symptoms improved shortly. She was suspected of congenital TTP because of no ADAMTS-13 inhibitor results and the persistent deficiency of ADAMTS-13 activity even after her condition improved. Pregnancy-onset TTP can cause nephrotic syndrome. Termination of pregnancy should be considered in cases with pregnancy-onset TTP to protect kidney function.

Infection as Trigger for Congenital Thrombotic Thrombocytopenic Purpura in an Adult Patient

Congenital thrombotic thrombocytopenic purpura (cTTP) is an inherited disease that is sometimes fatal in early childhood. cTTP is similar to idiopathic thrombotic thrombocytopenic purpura (iTTP); both are characterized by varying levels of thrombocytopenia, microangiopathic hemolytic anemia (MAHA), and end-organ damage secondary to occlusion of the microvasculature. cTTP is caused by a partial or total deficiency or loss of function of ADAMTS-13 (a disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13). We report the case of a 33-year-old woman who was mistakenly diagnosed with primary immune thrombocytopenia (ITP) during childhood. The patient was referred to our center with dyspnea, fatigue, fever, and jaundice with no clinical bleeding. Laboratory features were compatible with MAHA; ADAMTS-13 activity was at 0%, with negativity for ADAMTS-13 antibodies. We concluded the final diagnosis was cTTP. The triggering factor identified for MAHA was a double infection: central venous catheter bacterial infection and atypical pneumonia. After 7 days of treatment with antibiotics and ongoing total plasma exchange (TPE), the patient responded favorably. Our patient received fresh frozen plasma (FFP) infusion once every 2 weeks, and prophylactic voriconazole remained under control at the time of writing. As demonstrated in this case, effective treatment of the trigger cause helps reduce the need for continuous FFP exposure and controls the MAHA.

The standard of care for immune thrombotic thrombocytopenic purpura today

Targeted therapy of immune thrombotic thrombocytopenic purpura (iTTP) requires acurate and prompt diagnosis and differentiation from complement-mediated hemolytic uremic syndrome and other causes of thrombotic microangiopathy. ADAMTS-13 (A Disintegrin And Metalloprotease with ThromboSpondin-1 Domain, member 13) evaluation (activity and inhibitors or anti-ADAMTS-13 IgG) is the key for diagnosis and further management of patients with suspected iTTP during acute episode and in clinical response or remission. Clinical trial results and real-world data have demonstrated the efficacy and safety of the triple therapy consisting of therapeutic plasma exchange, caplacizumab, and immunosuppressives (e.g., corticosteroids and rituximab) for acute iTTP. Such a therapeutic strategy has significantly accelerated the normalization of platelet counts, decreased the length of stays in the intensive care unit and the hospital, but most importantly reduced the mortality rate. The present review highlights some of the important advancements for the diagnosis and management of iTTP and proposes triple therapy as the standard of care for acute iTTP today.

De Novo Mutation of the ADAMTS13 Gene with Mesenteric Ischemia in an Infant with Congenital Thrombotic Thrombocytopenic Purpura

Introduction

Congenital thrombotic thrombocytopenic purpura (cTTP) is a rare autosomal recessive disease characterized by ADAMTS13 deficiency or a severe decrease in its activity that is caused by homozygous or combined heterozygous mutations in its encoding gene. Here, we describe a de novo genetic mutation of the ADAMTS13 gene and a rare complication of cTTP in a neonate. Case Presentation. A full-term baby boy developed tachypnea, bradycardia, and oxygen desaturation at 2 h of life and was shifted to the newborn intensive care unit. He was oliguric in the first 24 h of life and had one episode of epistaxis. Blood-stained urine was observed in the urine catheter, and a coffee-ground-colored fluid was drained from the orogastric tube. Histopathological analysis revealed gastric perforation with features of ischemic insult. On day 8, genetic analysis confirmed the diagnosis of autosomal recessive familial thrombotic thrombocytopenic purpura and revealed a unique homozygous deletion mutation on exon 23 of ADAMTS13: c.2883del p.(Cys962Alafs^∗3).

Conclusion

cTTP is a rare life-threatening autosomal recessive disease with a high mortality rate. Early detection and initiation of aggressive treatment with plasma infusion could be a life-saving strategy in such cases.

Annual incidence and severity of acute episodes in hereditary thrombotic thrombocytopenic purpura

Hereditary thrombotic thrombocytopenic purpura (hTTP) is a rare thrombotic microangiopathy characterized by severe congenital ADAMTS13 deficiency and recurring acute episodes causing morbidity and premature death. Information on the annual incidence and severity of acute episodes in patients with hTTP is largely lacking. This study reports prospective data on 87 patients from the Hereditary TTP Registry (clinicaltrials.gov #NCT01257269) for survival, frequency, and severity of acute episodes from enrollment until December 2019. The 87 patients, followed up for a median of 4.2 years (range, 0.01-15 years), had a median age at overt disease onset and at clinical diagnosis of 4.6 years and 18 years (range, 0.0-70 years for both), respectively. Forty-three patients received regular plasma prophylaxis, whereas 22 did not, and treatment changed over time or was unknown in the remaining 22. Forty-three patients experienced 131 acute episodes, of which 91 (69%) occurred in patients receiving regular prophylaxis. This resulted in an annual incidence of acute episodes of 0.36 (95% confidence interval [CI], 0.29-0.44) with regular plasma treatment and of 0.41 (95% CI, 0.30-0.56) without regular plasma treatment. More than one-third of acute episodes (n = 51) were documented in children <10 years of age at enrollment and were often triggered by infections. Their annual incidence of acute episodes was significantly higher than in patients aged >40 years (1.18 [95% CI, 0.88-1.55] vs 0.14 [95% CI, 0.08-0.23]). The prophylactic plasma infusion regimens used were insufficient to prevent acute episodes in many patients. Such regimens are burdensome, and caregivers, patients, and their guardians are reluctant to start regular plasma infusions, from which children particularly would benefit.

Current prophylactic plasma infusion protocols do not adequately prevent long-term cumulative organ damage in the Japanese congenital thrombotic thrombocytopenic purpura cohort

Congenital thrombotic thrombocytopenic purpura (cTTP), known as Upshaw-Schulman syndrome, is an ultrarare thrombotic disorder caused by ADAMTS13 gene mutations; however, its long-term outcomes have not been widely studied. A questionnaire survey was administered to physicians of patients in the Japanese cTTP registry to characterise these outcomes. We analysed 55 patients in remission, with 41 cases receiving prophylactic fresh frozen plasma (FFP; median dosage: 13·2 ml/kg per month) and 14 receiving on-demand FFP. Patients receiving prophylactic FFP were considered as having a more severe form of the disease and had lower platelet counts and higher serum creatinine levels than those receiving on-demand FFP (median 138 × 10⁹ /l vs. 243 × 10⁹ /l, P = 0·003 and 0·71 mg/dl vs 0·58 mg/dl, P = 0·009, respectively). Patients who received prophylactic FFP more commonly developed organ damage, including renal impairment, cerebral infarctions, and cardiac hypofunction, than those who did not. Adverse FFP-related events were seen in 78% of the prophylactic FFP group, with allergic reactions being most common. Since current protocols for FFP administration to the prophylactic FFP group in Japan may be insufficient for preventing cumulative organ damage, a higher dosage of ADAMTS13 supply using recombinant ADAMTS13 agent is needed in these patients.

[Recurrent thrombocytopenia with hemolytic anemia in a boy aged 3 years]

A boy, aged 3 years and 8 months, had recurrent thrombocytopenia with hemolytic anemia for more than 3 years. The physical examination showed no enlargement of the liver, spleen, and lymph nodes or finger deformities. Laboratory results showed a negative result of the direct antiglobulin test, normal coagulation function, and increases in bilirubin, lactate dehydrogenase and reticulocytes. The results of von Willebrand factor-cleaving protease ADAMTS13 activity assay showed extreme deficiency, and antibody assay showed negative ADAMTS13 inhibitory autoantibodies. Next-generation sequence showed compound heterozygous mutation in the ADAMTS13 gene. The boy was diagnosed with congenital thrombotic thrombocytopenic purpura. This disease may be easily misdiagnosed as Evans syndrome and is difficult to diagnose in clinical practice. The child had developed the disease since birth, but it took 3 years to make a confirmed diagnosis. Therefore, congenital thrombotic thrombocytopenic purpura should be considered for children with jaundice at birth, recurrent thrombocytopenia with hemolytic anemia, and negative results of the direct antiglobulin test. The detection of ADAMTS13 activity and ADAMTS13 inhibitory autoantibodies should be performed as soon as possible for a definite diagnosis, and gene detection should be performed to make a confirmed diagnosis when necessary.

Hereditary Thrombotic Thrombocytopenic Purpura in a 9-Month-old: Diagnosing and Managing an Ultra-rare Disorder

Hereditary thrombotic thrombocytopenic purpura is an ultra-rare disorder caused by biallelic mutations in the ADAMTS13 gene. Because it can be difficult to diagnose, plasma ADAMTS13 activity assessment should be considered in patients with thrombocytopenia, anemia, and schistocytes on peripheral blood smear. We present the diagnostic evaluation of a patient with hereditary thrombotic thrombocytopenic purpura. Genetic testing revealed one known pathogenic mutation and one novel mutation of ADAMTS13 classified as likely pathogenic on the basis of parental genetic testing and in silico analyses. We further discuss off-label use of prophylactic plasma-derived Factor VIII (Koate-DVI) and the benefit of rare disease registries.

[Recurrent thrombocytopenia with hemolytic anemia in a boy aged 3 years]

A boy, aged 3 years and 8 months, had recurrent thrombocytopenia with hemolytic anemia for more than 3 years. The physical examination showed no enlargement of the liver, spleen, and lymph nodes or finger deformities. Laboratory results showed a negative result of the direct antiglobulin test, normal coagulation function, and increases in bilirubin, lactate dehydrogenase and reticulocytes. The results of von Willebrand factor-cleaving protease ADAMTS13 activity assay showed extreme deficiency, and antibody assay showed negative ADAMTS13 inhibitory autoantibodies. Next-generation sequence showed compound heterozygous mutation in the ADAMTS13 gene. The boy was diagnosed with congenital thrombotic thrombocytopenic purpura. This disease may be easily misdiagnosed as Evans syndrome and is difficult to diagnose in clinical practice. The child had developed the disease since birth, but it took 3 years to make a confirmed diagnosis. Therefore, congenital thrombotic thrombocytopenic purpura should be considered for children with jaundice at birth, recurrent thrombocytopenia with hemolytic anemia, and negative results of the direct antiglobulin test. The detection of ADAMTS13 activity and ADAMTS13 inhibitory autoantibodies should be performed as soon as possible for a definite diagnosis, and gene detection should be performed to make a confirmed diagnosis when necessary.

Assessing thrombogenesis and treatment response in congenital thrombotic thrombocytopenic purpura

Despite clinical remission and normal platelet counts, congenital TTP (cTTP) is associated with non-overt symptoms. Prophylactic ADAMTS13 replacement therapy such as plasma infusion (PI) prevents acute episodes and improves symptomatology. There is no current method to investigate disease severity or monitor the impact of treatment. We utilize a dynamic high shear flow assay to further understand disease pathophysiology and determine the impact of cTTP on symptomatology and therapy, despite normal platelet counts. Whole blood, under high shear, was run over collagen-coated channels, causing platelet adhesion to von Willebrand factor (VWF) multimers. The resulting surface coverage by platelet-VWF thrombus was assessed. The normal range was 6-39% in 50 controls. Twenty-two cTTP patients with normal platelet counts were evaluated. Median pre-treatment surface coverage was 89%, and PI reduced coverage to a median of 44% (p = 0.0005). Patients taking antiplatelets had further reduced coverage when combined with PI and improved non-overt symptoms such as headache, lethargy, and abdominal pain in 100% of patients compared to 74% with PI alone (p = 0.046). We use a dynamic assay to report increased in vitro platelet adhesion and aggregation and additionally demonstrate significantly decreased thrombi following PI, with levels in the normal range levels achieved in patients taking additional antiplatelet therapy.

Recognizing and managing hereditary and acquired thrombotic thrombocytopenic purpura in infants and children

We describe how infants and children with hereditary and acquired autoimmune thrombotic thrombocytopenic purpura (TTP) initially present and how they can be promptly diagnosed and effectively managed. These are uncommon disorders that are commonly misdiagnosed and can be rapidly fatal. TTP is caused by a severe deficiency of the plasma protease, A disintegrin and Metalloprotease with a ThromboSpondin type 1 motif, member 13 (ADAMTS13). Measurement of ADAMTS13 activity is becoming easily accessible. A common presentation of hereditary TTP is neonatal severe hemolysis and hyperbilirubinemia. However, the median age of diagnosis is not until 5.5 years. Plasma is effective treatment for exacerbations and for prophylaxis. Plasma may be replaced by recombinant ADAMTS13 when it becomes available. Acquired TTP is more frequent in older children, in whom it is more common in girls and is commonly associated with systemic lupus erythematosus. For acquired TTP, plasma exchange and immunosuppression are the current treatment for acute episodes; caplacizumab is now commonly used in adults and may replace plasma exchange.

Diagnosis of Hereditary TTP Caused by Homozygosity for a Rare Complex ADAMTS13 Allele After Salmonella Infection in a 43-Year-Old Asylum Seeker

A 43-year-old Armenian patient was diagnosed with salmonella infection and thrombotic microangiopathy (TMA). The clinical course was benign with resolution of all laboratory alterations after antibiotic treatment. Constantly deficient ADAMTS13 activity without ADAMTS13 inhibitors and evidence of homozygosity for a rare complex ADAMTS13 allele led to the diagnosis of congenital thrombotic thrombocytopenic purpura (cTTP). Half-life of ADAMTS13 after plasma infusion was calculated (27,6h) and double blinded plasma infusion as well as ergometric exercise with and without prior plasma infusion undertaken to investigate suspected smoldering TTP activity.

Cerebrovascular manifestations in hematological diseases: an update

Patients with hematological diseases often experience cerebrovascular complications including ischemic stroke, intracerebral and subarachnoid hemorrhage, microbleeds, posterior reversible encephalopathy syndrome, and dural sinus and cerebral vein thrombosis (CVT). In this update, we will review recent advances in the management of cerebrovascular diseases in the context of myeloproliferative neoplasms, leukemias, lymphomas, multiple myeloma, POEMS, paroxysmal nocturnal hemoglobinuria (PNH), thrombotic thrombocytopenic purpura (TTP), and sickle-cell disease. In acute ischemic stroke associated with hematological diseases, thrombectomy can in general be applied if there is a large vessel occlusion. Intravenous thrombolysis can be used in myeloproliferative neoplasms and sickle-cell anemia, but in other diseases, a case-by-case evaluation of the bleeding risks is mandatory. Patients with sickle-cell disease and acute stroke need very often to be transfused. In PNH, acute ischemic stroke patients must be anticoagulated. Most patients with CVT can be treated with low-molecular weight heparin (LMWH) acutely, even those with leukemias. Prevention of recurrence of cerebral thrombotic events depends on the control of the underlying disease, combined in some conditions with antithrombotic drugs. The recent introduction of specific monoclonal antibodies in the treatment of PHN and TTP has dramatically reduced the risk of arterial and venous thrombosis.

Thrombotic Thrombocytopenic Purpura: Pathophysiology, Diagnosis, and Management

Thrombotic thrombocytopenic purpura (TTP) is a rare thrombotic microangiopathy characterized by microangiopathic hemolytic anemia, severe thrombocytopenia, and ischemic end organ injury due to microvascular platelet-rich thrombi. TTP results from a severe deficiency of the specific von Willebrand factor (VWF)-cleaving protease, ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 repeats, member 13). ADAMTS13 deficiency is most commonly acquired due to anti-ADAMTS13 autoantibodies. It can also be inherited in the congenital form as a result of biallelic mutations in the ADAMTS13 gene. In adults, the condition is most often immune-mediated (iTTP) whereas congenital TTP (cTTP) is often detected in childhood or during pregnancy. iTTP occurs more often in women and is potentially lethal without prompt recognition and treatment. Front-line therapy includes daily plasma exchange with fresh frozen plasma replacement and immunosuppression with corticosteroids. Immunosuppression targeting ADAMTS13 autoantibodies with the humanized anti-CD20 monoclonal antibody rituximab is frequently added to the initial therapy. If available, anti-VWF therapy with caplacizumab is also added to the front-line setting. While it is hypothesized that refractory TTP will be less common in the era of caplacizumab, in relapsed or refractory cases cyclosporine A, N-acetylcysteine, bortezomib, cyclophosphamide, vincristine, or splenectomy can be considered. Novel agents, such as recombinant ADAMTS13, are also currently under investigation and show promise for the treatment of TTP. Long-term follow-up after the acute episode is critical to monitor for relapse and to diagnose and manage chronic sequelae of this disease.

Genomic investigation of inherited thrombotic microangiopathy-aHUS and TTP

Thrombotic microangiopathies (TMA) are a heterogeneous group of red cell fragmentation syndromes characterized by a tendency for thrombosis and pathognomonic red cell fragments in peripheral blood, which results in thrombosis in the microvasculature due to endothelial damage. Genomic investigations into inherited TMAs are of diagnostic, prognostic and therapeutic value. Here, we present two cases that capture the importance of performing genomic testing in rare disorders. Treatment options for these conditions, such as plasma exchange and monoclonal antibodies against complement factors, are intensive and expensive health care interventions. The results of genomic investigation into rare TMAs can better inform the clinicians and their patients of prognosis and suitable personalized treatment options.

First reported case of congenital thrombotic thrombocytopenic purpura in Taiwan with novel mutation of ADAMTS13 gene

Congenital thrombotic thrombocytopenic purpura (cTTP) is a rare disease that is defined as biallelic mutations of ADAMTS13 causing persistent absence of ADAMTS13 activity. The confirmed diagnosis requires a genetic study, and cTTP has never been previously reported in Taiwan. Our patient was a 29-year-old Taiwanese woman who presented with severe hyperbilirubinemia at birth. She had severe thrombocytopenia and hemolytic anemia at the age of 1, and another acute TTP event at the age of 7 triggered by an upper airway infection. Regular plasma replacement was started at age 12 based on a presumptive diagnosis of cTTP. Clinical diagnosis of cTTP, with undetectable ADAMTS13 activity and absence of ADAMTS13 inhibitor, was confirmed at age 27. A genetic study showed a previously reported mutation c.1921G to A, inherited from her father, and a maternally inherited, novel mutation at exon 12, c.1435+1dupG, which results in a splicing site change and frame shift. Reports of cTTP from East Asia, except Japan, are scarce. Some prevalent ADAMTS13 mutations are also race or region specific. With this report, we hope to raise awareness among physicians in Taiwan, promote early, proper diagnosis of cTTP, and reveal the true prevalence of cTTP in the Taiwanese population.

[Diagnosis of thrombotic thrombocytopenic purpura]

Thrombotic thrombocytopenic purpura (TTP) is a rare, life-threatening disease, disease, characterised by microangiopathic hemolytic anaemia, consumption thrombocytopenia, and organ dysfunction. The pathogenesis of TTP is attributed to the deficiency in the activity of the metalloproteinase ADAMTS13, specific von Willebrand factor cleaving protease. TTP is suspected when detecting microangiopathic hemolytic anemia, thrombocytopenia, damage to various organs. Diagnosis of TTP is confirmed by the detection of ADAMTS13 activity in plasma less than 10%. Plasma samples for the study of ADAMTS13 activity should be taken before the start of plasma transfusions or plasma exchange. In patients with severe ADAMTS-13 deficiency autoantibodies anti-ADAMTS13 and inhibitor ADAMTS13 should be investigated. Anti-ADAMTS13 antibodies belonging to IgG not always have inhibitory effects. The inhibitory effect of anti-ADAMTS13 antibodies is confirmed by mixing test. All patients with the first established diagnosis of TTP should be examined for mutations of the ADAMTS13 gene.

Insights from the Hereditary Thrombotic Thrombocytopenic Purpura Registry: Discussion of Key Findings Based on Individual Cases from Switzerland

The Hereditary TTP Registry is an international cohort study for patients with a confirmed or suspected diagnosis of hereditary thrombotic thrombocytopenic purpura (hTTP) and their family members. Hereditary TTP is an ultra-rare blood disorder (prevalence of ∼1-2 cases per million), the result of autosomal-recessively inherited congenital ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) deficiency (ADAMTS13 activity <10% of the normal), and associated with yet many unanswered questions. Until December 2017, the Hereditary TTP Registry had enrolled 123 confirmed hTTP patients. Their median age at disease onset was 4.5 years (range: 0-70) and at clinical diagnosis 16.7 years (range: 0-69), a difference that highlights the existing awareness gap in recognizing hTTP. The systematic collection of clinical data of individual patients revealed their substantial baseline comorbidities, as a consequence of recurring TTP episodes in the past. Most notable was the high proportion of patients having suffered from premature arterial thrombotic events, mainly transient ischemic attacks, ischemic strokes, and to a lesser extent myocardial infarctions. At 40 to 50 years of age and above, more than 50% of patients had suffered from at least one such event, and many had experienced arterial thrombotic events despite regular plasma infusions every 2 to 3 weeks that supplements the missing plasma ADAMTS13. The article by van Dorland et al. (Haematologica 2019;104(10):2107-2115) and the ongoing Hereditary TTP Registry cohort study were recognized with the Günter Landbeck Excellence Award at the 50th Hemophilia Symposium in Hamburg in November 2019, the reason to present the Hereditary TTP Registry in more detail here.

Exome Sequencing Identifies Abnormalities in Glycosylation and ANKRD36C in Patients with Immune-Mediated Thrombotic Thrombocytopenic Purpura

BACKGROUND

 Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a potentially fatal blood disorder, resulting from autoantibodies against ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13). However, the mechanism underlying anti-ADAMTS13 autoantibody formation is not known, nor it is known how genetic aberrations contribute to the pathogenesis of iTTP.

METHODS

 Here we performed whole exome sequencing (WES) of DNA samples from 40 adult patients with iTTP and 15 local healthy subjects with no history of iTTP and other hematological disorders.

RESULTS

 WES revealed variations in the genes involved in protein glycosylation, including O-linked glycosylation, to be a major pathway affected in patients with iTTP. Moreover, variations in the ANKRD gene family, particularly ANKRD36C and its paralogs, were also more prevalent in patients with iTTP than in the healthy controls. The ANKRD36 family of proteins have been implicated in inflammation. Mass spectrometry revealed a dramatic alternation in plasma glycoprotein profile in patients with iTTP compared with the healthy controls.

CONCLUSION

 Altered glycosylation may affect the disease onset and progression in various ways: it may predispose patients to produce ADAMTS13 autoantibodies or affect their binding properties; it may also alter clearance kinetics of hemostatic and inflammatory proteins. Together, our findings provide novel insights into plausible mechanisms underlying the pathogenesis of iTTP.

Why thromboembolism occurs in some patients with thrombocytopenia and treatment strategies

Platelets play such an important role in the process of thrombosis that patients with thrombocytopenia generally have an increased risk of bleeding. However, abnormal thrombotic events can sometimes occur in patients with thrombocytopenia, which is unusual and inexplicable. The treatments for thrombocytopenia and thromboembolism are usually contradictory. This review introduces the mechanisms of thromboembolism in patients with different types of thrombocytopenia and outlines treatment recommendations for the prevention and treatment of thrombosis. According to the cause of thrombocytopenia, this article addresses four etiologies, including inherited thrombocytopenia (Myh9-related disease, ANKRD26-associated thrombocytopenia, Glanzmann thrombasthenia, Bernard-Soulier syndrome), thrombotic microangiopathy (thrombotic thrombocytopenic purpura, atypical hemolytic uremic syndrome, hemolytic uremic syndrome, Hemolysis Elevated Liver enzymes and Low Platelets syndrome, disseminated intravascular coagulation), autoimmune-related thrombocytopenia (immune thrombocytopenic purpura, antiphospholipid syndrome, systemic lupus erythematosus), and acquired thrombocytopenia (Infection-induced thrombocytopenia and drug-induced thrombocytopenia, heparin-induced thrombocytopenia). We hope to provide more evidence for clinical applications and future research.

ISTH guidelines for treatment of thrombotic thrombocytopenic purpura

BACKGROUND

Despite advances in treatment options for thrombotic thrombocytopenic purpura (TTP), there are still limited high quality data to inform clinicians regarding its appropriate treatment.

METHODS

In June 2018, the ISTH formed a multidisciplinary guideline panel to issue recommendations about treatment of TTP. The panel discussed 12 treatment questions related to immune-mediated TTP (iTTP) and hereditary or congenital TTP (cTTP). The panel used the Grading of Recommendations Assessment, Development, and Evaluation approach, including evidence-to-decision frameworks, to appraise evidence and formulate recommendations.

RESULTS

The panel agreed on 11 recommendations based on evidence ranging from very low to moderate certainty. For first acute episode and relapses of iTTP, the panel made a strong recommendation for adding corticosteroids to therapeutic plasma exchange (TPE) and a conditional recommendation for adding rituximab and caplacizumab. For asymptomatic iTTP with low plasma ADAMTS13 activity, the panel made a conditional recommendation for the use of rituximab outside of pregnancy, but prophylactic TPE during pregnancy. For asymptomatic cTTP, the panel made a strong recommendation for prophylactic plasma infusion during pregnancy, and a conditional recommendation for plasma infusion or a wait and watch approach outside of pregnancy.

CONCLUSIONS

The panel's recommendations are based on all the available evidence for the effects of an individual component of various treatment approaches, including suppressing inflammation, blocking platelet clumping, replacing the missing and/or inhibited ADAMTS13, and suppressing the formation of ADAMTS13 autoantibody. There was insufficient evidence for further comparing different treatment approaches (eg, TPE, corticosteroids, rituximab, and caplacizumab, etc.), for which high quality studies are needed.

ISTH guidelines for the diagnosis of thrombotic thrombocytopenic purpura

BACKGROUND

Despite an increase in our understandings of pathogenesis of thrombotic thrombocytopenic purpura (TTP), the approaches for initial diagnosis and management of TTP vary significantly.

OBJECTIVE

The evidence-based guidelines of the International Society on Thrombosis and Haemostasis (ISTH) are intended to support patients, clinicians, and other health care professionals in their decisions about the initial diagnosis and management of acute TTP.

METHODS

In June 2018, ISTH formed a multidisciplinary panel that included hematologists, an intensive care physician, nephrologist, clinical pathologist, biostatistician, and patient representatives, as well as a methodology team from McMaster University. The panel composition was designed to minimize the potential conflicts of interests. The panel used the Grading of Recommendations Assessment, Development, and Evaluation approach and the Population, Intervention, Comparison, Outcome framework to develop and grade their recommendations. Public comments were sought and incorporated in the final document.

RESULTS

The panel agreed on three recommendations covering the initial diagnosis with emphasis on the importance of ADAMTS13 testing (eg, activity, anti-ADAMTS13 IgG or inhibitor) and assessment of the pretest probability of TTP by clinical assessment and/or the risk assessment models like the PLASMIC or French score. The panel noted how availability and turnaround time of ADAMTS13 test results might affect early diagnosis and management, in particular the use of caplacizumab.

CONCLUSIONS

There is a lack of high-quality evidence to support strong recommendations for the initial diagnosis and management of a suspected TTP. The panel emphasized the importance of obtaining ADAMTS13 testing in a proper clinical context. Future research should focus on how to monitor and act on ADAMTS13 levels during remission.

Patent ductus arteriosus generates neonatal hemolytic jaundice with thrombocytopenia in Upshaw-Schulman syndrome

One third of patients with USS have a neonatal episode of severe hemolytic jaundice with thrombocytopenia induced by an unknown trigger. A USS patient with persisting PDA and recurrent neonatal hemolysis/thrombocytopenia suggests blood flow through the PDA as trigger.

In silico features of ADAMTS13 contributing to plasmatic ADAMTS13 levels in neonates with congenital heart disease

INTRODUCTION

Risk factors contributing to heightened thrombosis in pediatric congenital heart disease (CHD) patients are not fully understood. Among the neonatal CHD population, those presenting with single ventricular physiology are at the highest risk for perioperative thrombosis. The von Willebrand factor and ADAMTS13 interactions have emerged as causative risk factors for pediatric stroke and could contribute to heightened thrombosis in CHD neonates.

METHODS

This study investigates a cohort of children with single ventricle physiology and undergoing cardiac surgery, during which some patients developed thrombosis. In this cohort, we analyzed the relationship of several molecular features of ADAMTS13 with the plasma and activity levels in patients at risk of thrombosis. Additionally, in light of the natural antithrombotic activity of ADAMTS13, we have sequenced the ADAMTS13 gene for each patient and evaluated the role of genetic variants in determining the plasma ADAMTS13 levels using a series of in silico tools including Hidden Markov Models, EVmutation, and Rosetta.

RESULTS

Lower ADAMTS13 levels were found in patients that developed thrombosis. A novel in silico analysis to assess haplotype effect of co-occurring variants identified alterations in relative surface area and solvation energy as important contributors. Our analysis suggested that beneficial or deleterious effect of a variant can be reasonably predicted by comprehensive analysis of in silico assessment and in vitro and/or in vivo data.

CONCLUSION

Findings from this study add to our understanding the role of genetic features of ADAMTS13 in patients at high risk of thrombosis related to an imbalanced relation between VWF and ADAMTS13.

Histone-induced thrombotic thrombocytopenic purpura in adamts13 -/- zebrafish depends on von Willebrand factor

Thrombotic thrombocytopenic purpura (TTP) is caused by severe deficiency of ADAMTS13 (A13), a plasma metalloprotease that cleaves endothelium-derived von Willebrand factor (VWF). However, severe A13 deficiency alone is often not sufficient to cause an acute TTP; additional factors may be required to trigger the disease. Using CRISPR/Cas9, we created and characterized several novel zebrafish lines carrying a null mutation in a13-/- , vwf, and both. We further used these zebrafish lines to test the hypothesis that inflammation that results in neutrophil activation and release of histone/DNA complexes may trigger TTP. As shown, a13-/- zebrafish exhibit increased levels of plasma VWF antigen, multimer size, and ability of thrombocytes to adhere to a fibrillar collagen-coated surface under flow. The a13-/- zebrafish also show an increased rate of occlusive thrombus formation in the caudal venules after FeCl3 injury. More interestingly, a13-/- zebrafish exhibit ~30% reduction in the number of total, immature, and mature thrombocytes with increased fragmentation of erythrocytes. Administration of a lysine-rich histone results in more severe and persistent thrombocytopenia and a significantly increased mortality rate in a13-/- zebrafish than in wildtype (wt) ones. However, both spontaneous and histone-induced TTP in a13-/- zebrafish are rescued by the deletion of vwf These results demonstrate a potentially mechanistic link between inflammation and the onset of TTP in light of severe A13 deficiency; the novel zebrafish models of TTP may help accelerate our understanding of pathogenic mechanisms and the discoveries of novel therapeutics for TTP and perhaps other arterial thrombotic disorders.

Genomic Landscape and Mutational Spectrum of ADAMTS Family Genes in Mendelian Disorders Based on Gene Evidence Review for Variant Interpretation

ADAMTS (a disintegrin and metalloproteinase with thrombospondin motifs) are a family of multidomain extracellular protease enzymes with 19 members. A growing number of ADAMTS family gene variants have been identified in patients with various hereditary diseases. To understand the genomic landscape and mutational spectrum of ADAMTS family genes, we evaluated all reported variants in the ClinVar database and Human Gene Mutation Database (HGMD), as well as recent literature on Mendelian hereditary disorders associated with ADAMTS family genes. Among 1089 variants in 14 genes reported in public databases, 307 variants previously suggested for pathogenicity in Mendelian diseases were comprehensively re-evaluated using the American College of Medical Genetics and Genomics (ACMG) 2015 guideline. A total of eight autosomal recessive genes were annotated as being strongly associated with specific Mendelian diseases, including two recently discovered genes (ADAMTS9 and ADAMTS19) for their causality in congenital diseases (nephronophthisis-related ciliopathy and nonsyndromic heart valve disease, respectively). Clinical symptoms and affected organs were extremely heterogeneous among hereditary diseases caused by ADAMTS family genes, indicating phenotypic heterogeneity despite their structural and functional similarity. ADAMTS6 was suggested as presenting undiscovered pathogenic mutations responsible for novel Mendelian disorders. Our study is the first to highlight the genomic landscape of ADAMTS family genes, providing an appropriate genetic approach for clinical use.

Hereditary Thrombotic Thrombocytopenic Purpura in a Chinese Boy With a Novel Compound Heterozygous Mutation of the ADAMTS13 Gene

Hereditary thrombotic thrombocytopenic purpura (TTP) is caused by ADAMTS13 mutations with autosomal recessive inheritance. It typically presents during childhood and is frequently misdiagnosed as immune thrombocytopenia. We present a case of hereditary TTP with an undescribed compound heterozygous ADAMTS13 mutation in a Chinese boy. A 12-year-old boy with a history of intermittent thrombocytopenia in the prior 6 years had severe deficiency of plasma ADAMTS13 and harbored a novel compound heterozygous mutation which was also identified in his sister. The c.577C>T was a pathogenic variant reported exclusively in Japanese cases. The undescribed c.2397C>A non-sense mutation was predicted to encode a truncated protein. Identification of the specific novel heterozygous ADAMTS13 mutation in the Chinese family, consisting a variant restricted to Asian individuals and an undescribed c.2397C>A non-sense mutation, demonstrates genetic diversity underlying hereditary TTP, and possibly ethnic skewed mutation profiles.

Stroke and myocardial infarction in hereditary thrombotic thrombocytopenic purpura: similarities to sickle cell anemia

Stroke is common in hereditary thrombotic thrombocytopenic purpura (TTP) patients, occurring in 25% to 31% of patients. In hereditary TTP patients, the age of occurrence of first stroke (median, 19 years) is similar to that for sickle cell anemia patients.

Diagnostic Testing for Differential Diagnosis in Thrombotic Microangiopathies

Thrombotic microangiopathies (TMAs) are multiple disease entities with different etiopathogeneses, characterized by thrombocytopenia, microangiopathic hemolytic anemia (MAHA) with schistocytosis, variable symptoms including fever, and multi-organ failure such as mild renal impairment and neurological deficits. The two paradigms of TMAs are represented on one hand by acquired thrombotic thrombocytopenic purpura (TTP) and on the other by hemolytic uremic syndrome (HUS). The differential diagnosis between these two paradigmatic forms of TMA is based on the presence of either frank renal failure in HUS or a severe deficiency (<10%) of the zinc-protease ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) in TTP. ADAMTS13 is an enzyme involved in the proteolytic processing of von Willebrand factor (vWF), and its deficiency results in formation of high-molecular-weight vWF-rich microthrombi in the environment of the microvasculature. The presence of these ultra-large vWF multimers in the microcirculation can recruit platelets, promoting multi-organ ischemic lesions. The presence of ADAMTS13 activity at >10% could rule out the presence of a TTP form. However, it is often difficult to differentiate either a TTP or HUS clinical scenario presenting with typical symptoms of TMA. There are in fact several additional diagnoses that should be considered in patients with ADAMTS13 activity of >10%. Widespread inflammation with endothelial damage and adverse reactions to drugs play a central role in the pathogenesis of several forms of TMA, and in these cases, the differential diagnosis should be directed at the underlying disease. Hence, a correct etiologic diagnosis of TMA should involve a critical illness, cancer-associated TMA, drug-induced TMA, and hematopoietic transplant-associated TMA. A complete assessment of all the possible etiologies for TMA symptoms, including acquired or congenital TTP, will allow for a more accurate diagnosis and application of a more appropriate treatment.

Synergistic effects of ADAMTS13 deficiency and complement activation in pathogenesis of thrombotic microangiopathy

Severe deficiency of plasma ADAMTS13 activity is the primary cause of thrombotic thrombocytopenic purpura (TTP) whereas overwhelming activation of complement via an alternative pathway results in atypical hemolytic uremic syndrome (aHUS), the prototypes of thrombotic microangiopathy (TMA). However, clinical and pathogenic distinctions between TTP and aHUS are often quite challenging. Clinical reports have suggested that complement activation may play a role in the development of TTP, which is caused by severe deficiency of plasma ADAMTS13 activity. However, the experimental evidence to support this hypothesis is still lacking. Here, we show that mice with either Adamts13 -/- or a heterozygous mutation of complement factor H (cfh) at amino acid residue of 1206 (ie, cfh W/R ) alone remain asymptomatic despite the presence of occasional microvascular thrombi in various organ tissues. However, mice carrying both Adamts13 -/- and cfh W/R exhibit thrombocytopenia, low haptoglobin, increased fragmentation of erythrocytes in peripheral blood smear, increased plasma levels of lactate dehydrogenase activity, blood urea nitrogen, and creatinine, as well as an increased mortality rate, consistent with the development of TMA. Moreover, mice with a homozygous mutation of cfh (ie, cfh R/R ) with or without Adamts13 -/- developed severe TMA. The mortality rate in mice with Adamts13 -/- cfh R/R was significantly higher than that in mice with cfh R/R alone. Histological and immunohistochemical analyses demonstrated the presence of disseminated platelet-rich thrombi in terminal arterioles and capillaries of major organ tissues in these mice that were either euthanized or died. Together, our results support a synergistic effect of severe ADAMTS13 deficiency and complement activation in pathogenesis of TMA in mice.

Reduced ADAMTS13 activity during TTP remission is associated with stroke in TTP survivors

With timely and effective treatment, most patients with thrombotic thrombocytopenic purpura (TTP) survive the acute TTP episode. In addition to the risk of relapse, TTP survivors have higher all-cause mortality than the general population and increased rates of chronic morbidities, including hypertension, depression, and mild cognitive impairment. We conducted this retrospective-prospective cohort study to determine the incidence and prevalence of stroke after recovery from acute TTP and to test the hypothesis that lower ADAMTS13 activity after recovery from TTP is associated with an increased risk of stroke during remission. Of 170 consecutive patients treated for TTP at The Johns Hopkins Hospital from 1995 through 2018, 14 (8.2%) died during the index episode and 19 were observed for less than 1 month after recovery. Of the remaining 137 patients, 18 (13.1%) developed stroke unrelated to an acute TTP episode over a median observation period of 3.08 years, which is fivefold higher than the expected prevalence of 2.6% from an age- and sex-matched reference population (P = .002). ADAMTS13 activity during remission was measured in 52 patients and was >70% in 44.2%, 40% to 70% in 23.1%, 10% to 39% in 25%, and <10% in 7.7%. Stroke after recovery from acute TTP occurred in 0% (0 of 22) of patients with normal remission ADAMTS13 activity (>70%) and in 27.6% (8 of 29) of patients with low ADAMTS13 activity (≤70%; P = .007). In conclusion, stroke is common after recovery from TTP and is associated with reduced ADAMTS13 activity during remission.

ADAMTS13: An Emerging Target in Stroke Therapy

Thrombosis is the predominant underlying mechanism of acute ischemic stroke (AIS). Though thrombolysis with tPA has been proven to be effective in treating AIS within the time window, the majority of AIS patients fail to receive tPA due to various reasons. Current medical therapies for AIS have limited efficacy and pose a risk of intracerebral hemorrhage. ADAMTS13 (a disintegrin and metalloprotease with a thrombospondin type 1 motif, member 13) is a metalloprotease that effectively breaks down the von Willebrand Factor (VWF), a key factor in thrombus formation. Previous studies have proven that dysfunction of ADAMTS13 is associated with many diseases. Recently, ADAMTS13 has been reported to be closely related to stroke. In this review, we briefly described the structure of ADAMTS13 and its role in thrombosis, inflammation, as well as angiogenesis. We then focused on the relationship between ADAMTS13 and AIS, ranging from ischemic stroke occurrence, to AIS treatment and prognosis. Based on research findings from in vitro, animal, and clinical studies, we propose that ADAMTS13 is a potential biomarker to guide appropriate treatment for ischemic stroke and a promising therapeutic agent for tPA resistant thrombi.