Thrombotic thrombocytopenic purpura in children

Immunosuppressive Therapy of Antibody-Mediated aHUS and TTP

The recent classification of pediatric thrombotic microangiopathies (TMA) takes into consideration mechanisms of disease for guidance to targeted therapies. We present our experience with seven patients with antibody mediated atypical hemolytic uremic syndrome (aHUS) and thrombotic thrombocytopenic purpura (TTP). Five children had aHUS with antibodies against complement factor H (CFH-ab) and two with TTP with antibodies against metalloproteinase ADAMTS13. In the aHUS cases diagnosed and treated before the eculizumab era, CFH-ab was detected using the ELISA assay. Mutational analysis of selected complement genes was performed. TTP was diagnosed if, in addition to microangiopathic hemolytic anemia and thrombocytopenia, ischemic organ involvement and severe deficiency in ADAMTS13 activity were present. Treatment protocol consisted of plasma exchanges (PE) and steroid pulses, followed by the combination of cyclophosphamide and rituximab to achieve long-term immunosuppression. Four patients with CFH-ab and the TTP patients with ADAMTS13 antibodies came into sustained remission. After a median follow-up of 11.7 (range 7.7-12.9) years without maintenance therapy, no disease recurrence was observed; nevertheless, six patients, two had hypertension and two had proteinuria as a late consequence. One patient, with late diagnosis of CFH-ab and additional genetic risk factors who was treated only with PE and plasma substitution, reached end-stage renal disease and was later successfully transplanted using eculizumab prophylaxis. In the cases of antibody-mediated TMAs, PE and early immunosuppressive treatment may result in sustained remission with preserved kidney function. Further data are needed to establish optimal treatment of anti-FH antibody-associated HUS.

Pharmacological Management of Atypical Hemolytic Uremic Syndrome in Pediatric Patients: Current and Future

Atypical hemolytic uremic syndrome is a thrombotic microangiopathy characterized by hemolysis, thrombocytopenia, and acute kidney injury, usually caused by alternative complement system overactivation due to pathogenic genetic variants or antibodies to components or regulatory factors in this pathway. Previously, a lack of effective treatment for this condition was associated with mortality, end-stage kidney disease, and the risk of disease recurrence after kidney transplantation. Plasma therapy has been used for atypical hemolytic uremic syndrome treatment with inconsistent results. Complement-blocking treatment changed the outcome and prognosis of patients with atypical hemolytic uremic syndrome. Early administration of eculizumab, a monoclonal C5 antibody, leads to improvements in hematologic, kidney, and systemic manifestations in patients with atypical hemolytic uremic syndrome, even with apparent dialysis dependency. Pre- and post-transplant use of eculizumab is effective in the prevention of atypical hemolytic uremic syndrome recurrence. Evidence on eculizumab use in secondary hemolytic uremic syndrome cases is controversial. Recent data favor the restrictive use of eculizumab in carefully selected atypical hemolytic uremic syndrome cases, but close monitoring for relapse after drug discontinuation is emphasized. Prophylaxis for meningococcal infection is important. The long-acting C5 monoclonal antibody ravulizumab is now approved for atypical hemolytic uremic syndrome treatment, enabling a reduction in the dosing frequency and improving the quality of life in patients with atypical hemolytic uremic syndrome. New strategies for additional and novel complement blockage medications in atypical hemolytic uremic syndrome are under investigation.

Recommendations for the diagnosis and treatment of patients with thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy (TMA) characterized by the development of microangiopathic haemolytic anaemia, thrombocytopenia, and ischaemic organ dysfunction associated with ADAMTS13 levels lower than 10% in most cases. Recently there have been numerous advances in the field of PTT, new, rapid and accessible techniques capable of quantifying ADAMTS13 activity and inhibitors. The massive sequencing systems facilitate the identification of polymorphisms in the ADAMTS13 gene. In addition, new drugs such as caplacizumab have appeared and relapse prevention strategies are being proposed with the use of rituximab. The existence of TTP patient registries allow a deeper understanding of this disease but the great variability in the diagnosis and treatment makes it necessary to elaborate guidelines that homogenize terminology and clinical practice. The recommendations set out in this document were prepared following the AGREE methodology. The research questions were formulated according to the PICO format. A search of the literature published during the last 10 years was carried out. The recommendations were established by consensus among the entire group, specifying the existing strengths and limitations according to the level of evidence obtained. In conclusion, this document contains recommendations on the management, diagnosis, and treatment of TTP with the ultimate objective of developing guidelines based on the evidence published to date that allow healthcare professionals to optimize TTP treatment.

An ADAMTS13 mutation that causes hereditary thrombotic thrombocytopenic purpura: a case report and literature review

Background

Mutations in the ADAMTS13 gene can lead to an ADAMTS13 enzyme deficiency, which is related to Upshaw–Schulman syndrome (USS). USS is a common type of thrombotic thrombocytopenic purpura (TTP). Here we present a very rare case of TTP caused by 2 mutations in the ADAMTS13 gene. Besides, we reviewed and summarized previous pathogenic ADAMTS13 gene mutations associated with the TTP.

Case presentation

A 10-year-old female was admitted to the Third Xiangya Hospital of Central South University after experiencing discontinuous thrombocytopenia for 8 years, abnormal renal function for more than 2 years, cough for more than 10 days, and weakness of the left limb for 3 days. Gene sequencing shows the patient’s ADAMTS13 gene contains compound heterozygous nucleotide variations: c.1335delC (p. Phe445LeufsTer52) is a frameshift variation inherited from her father and c.2130C > G (p. Cys710Trp) is a missense variation inherited from her mother. The final diagnosis was USS.

Conclusions

Our study reports a very rare genetic TTP case caused by two compound heterozygous variants in the ADAMTS13 gene. The effect of these two mutations on the secretion of ADAMTS13 requires further in vitro experiments to confirm.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12920-021-01099-3.

Thrombotic Thrombocytopenic Purpura in a Child Treated for Acute Lymphoblastic Leukemia: Case Report and Review of Literature

Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy caused by deficiency of von Willebrand factor-cleaving protease ADAMTS13. Large von Willebrand multimer formation and intravascular platelet aggregation affecting the arterioles and capillaries can result in death unless early treatment is administered. We report on the case of a child with TTP associated with a human herpes virus type-6 infection occurring during chemotherapy for acute lymphoblastic leukemia who was effectively treated by fresh frozen plasma infusions and antiviral therapy. Although rarely observed in children affected by acute lymphoblastic leukemia, TTP is a potentially fatal illness that should be considered in the differential diagnosis of thrombocytopenia with hemolytic anemia.

Acquired thrombotic thrombocytopenia purpura associated with severe ADAMTS13 deficiency in a 3-year-old boy: a case report and review of the literature

Background

Acquired thrombotic thrombocytopenia purpura is very rarely encountered in children. It is often misdiagnosed initially when the condition is not inherited.

Case presentation

We describe a 3-year-old Malay boy who presented with simple febrile seizure and had no neurological deficit, however, he was found to have microangiopathic hemolytic anemia, thrombocytopenia, and elevated serum lactate dehydrogenase. An ADAMTS13 assay results showed zero activities (0%), and markedly high level of ADAMTS13 inhibitor (93.15 U/mL) confirming the diagnosis of secondary thrombotic thrombocytopenia purpura. He received fresh frozen plasma infusions for 3 days and subsequently his platelet levels normalized. Serial ADAMTS13 assay results showed improvement. He was also given a short course of prednisolone after which the ADAMTS13 activity normalized (> 114%) at the end of prednisolone course.

Conclusions

At presentation, acquired thrombotic thrombocytopenia purpura in a very young child is commonly misdiagnosed as other conditions like idiopathic thrombocytopenic purpura, Evans syndrome, atypical hemolytic-uremic syndrome, or malignancy. ADAMTS13 assay should be performed early when thrombotic thrombocytopenia purpura is suspected as this condition is associated with dire consequences.

Child-onset thrombotic thrombocytopenic purpura caused by p.R498C and p.G259PfsX133 mutations in ADAMTS13

INTRODUCTION

Patients suffering from congenital thrombotic thrombocytopenic purpura (cTTP) have a deficiency in ADAMTS13 due to mutations in their ADAMTS13 gene.

OBJECTIVE

The aim of this study was to determine ADAMTS13 parameters (activity, antigen, and mutations), to investigate if the propositus suffered from child-onset cTTP, and to study the in vitro effect of the ADAMTS13 mutations.

METHODS

ADAMTS13 activity and antigen were determined using the FRETS VWF73 assay and ELISA and ADAMTS13 mutations via sequencing of the exons. Mutant proteins were expressed in Chinese hamster ovary cells, and their expression was studied using fluorescence microscopy and ELISA. Molecular modeling was used to evaluate the effect of the mutations on ADAMTS13 structure and stability.

RESULTS

The propositus was diagnosed with cTTP at the age of 20. ADAMTS13 activity was below 10%, and 2 compound heterozygous mutations, the p.R498C point and the p.G259PfsX133 frameshift mutation, were identified. Expression of ADAMTS13 mutants revealed that the p.R498C and the p.G259PfsX133 mutation cause secretion and translation defects in vitro, respectively. Molecular modeling showed that the R498 intra-domain interactions are lacking in the p.R498C mutant, resulting in protein instability.

CONCLUSION

The ADAMTS13 mutations result in a severe ADAMTS13 deficiency explaining the patient's phenotype.

Treatment and management of children with haemolytic uraemic syndrome

Haemolytic uraemic syndrome (HUS), comprising microangiopathic haemolytic anaemia, thrombocytopaenia and acute kidney injury, remains the leading cause of paediatric intrinsic acute kidney injury, with peak incidence in children aged under 5 years. HUS most commonly occurs following infection with Shiga toxin-producing Escherichia coli (STEC-HUS). Additionally, HUS can occur as a result of inherited or acquired dysregulation of the alternative complement cascade (atypical HUS or aHUS) and in the setting of invasive pneumococcal infection. The field of HUS has been transformed by the discovery of the central role of complement in aHUS and the dawn of therapeutic complement inhibition. Herein, we address these three major forms of HUS in children, review the latest evidence for their treatment and discuss the management of STEC infection from presentation with bloody diarrhoea, through to development of fulminant HUS.

Long-Term Prevention of Congenital Thrombotic Thrombocytopenic Purpura in ADAMTS13 Knockout Mice by Sleeping Beauty Transposon-Mediated Gene Therapy

OBJECTIVE

Severe deficiency in the von Willebrand factor-cleaving protease ADAMTS13 (a disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13) because of mutations in the ADAMTS13 gene can lead to acute episodes of congenital thrombotic thrombocytopenic purpura (TTP), requiring prompt treatment. Current treatment consists of therapeutic or prophylactic infusions of fresh frozen plasma. However, lifelong treatment with plasma products is a stressful therapy for TTP patients. Here, we describe the use of the nonviral sleeping beauty (SB) transposon system as a gene therapeutic approach to realize lifelong expression of ADAMTS13 and subsequent protection against congenital TTP.

APPROACH AND RESULTS

We demonstrated that hydrodynamic tail vein injection of the SB100X system expressing murine ADAMTS13 in Adamts13^-/- mice resulted in long-term expression of supraphysiological levels of transgene ADAMTS13 over a period of 25 weeks. Stably expressed ADAMTS13 efficiently removed the prothrombotic ultralarge von Willebrand factor multimers present in the circulation of Adamts13^-/- mice. Moreover, mice stably expressing ADAMTS13 were protected against TTP. The treated mice did not develop severe thrombocytopenia or did organ damage occur when triggered with recombinant von Willebrand factor, and this up to 20 weeks after gene transfer.

CONCLUSIONS

These data demonstrate the feasibility of using SB100X-mediated gene therapy to achieve sustained expression of transgene ADAMTS13 and long-term prophylaxis against TTP in Adamts13^-/- mice.

An international consensus approach to the management of atypical hemolytic uremic syndrome in children

Atypical hemolytic uremic syndrome (aHUS) emerged during the last decade as a disease largely of complement dysregulation. This advance facilitated the development of novel, rational treatment options targeting terminal complement activation, e.g., using an anti-C5 antibody (eculizumab). We review treatment and patient management issues related to this therapeutic approach. We present consensus clinical practice recommendations generated by HUS International, an international expert group of clinicians and basic scientists with a focused interest in HUS. We aim to address the following questions of high relevance to daily clinical practice: Which complement investigations should be done and when? What is the importance of anti-factor H antibody detection? Who should be treated with eculizumab? Is plasma exchange therapy still needed? When should eculizumab therapy be initiated? How and when should complement blockade be monitored? Can the approved treatment schedule be modified? What approach should be taken to kidney and/or combined liver-kidney transplantation? How should we limit the risk of meningococcal infection under complement blockade therapy? A pressing question today regards the treatment duration. We discuss the need for prospective studies to establish evidence-based criteria for the continuation or cessation of anticomplement therapy in patients with and without identified complement mutations.

Treatment of Congenital Thrombotic Thrombocytopenic Purpura With Eculizumab

A 12-year-old boy was hospitalized for hemolytic anemia, thrombocytopenia, acute kidney injury, and generalized seizures. The childhood onset, severely decreased kidney function, absence of prodromal diarrhea, negative test results for Shiga-like toxin-producing Escherichia coli, elevated plasma levels of the terminal complement complex sC5b-9, and ex vivo testing in endothelial cells showing serum-induced complement activation were all consistent with a diagnosis of complement-mediated atypical hemolytic uremic syndrome. Before plasma ADAMTS13 (von Willebrand factor protease) activity results were available, the patient was treated with the anti-C5 monoclonal antibody eculizumab, and treatment was followed by prompt disease remission. However, results of ADAMT13 activity level tests and gene screening revealed a severe deficiency associated with 2 heterozygous mutations in the ADAMTS13 gene, fully consistent with a diagnosis of congenital thrombotic thrombocytopenic purpura. Screening for atypical hemolytic uremic syndrome-associated genes failed to show a mutation and an assay for plasma anti-factor H antibodies gave negative results both before and after eculizumab treatment initiation. The patient's clinical evolution suggests that complement activation plays a role in the pathogenesis of thrombotic thrombocytopenic purpura and provides unexpected new insights into the treatment of this life-threatening disease.

ADAMTS13 Secretion and Residual Activity among Patients with Congenital Thrombotic Thrombocytopenic Purpura with and without Renal Impairment

BACKGROUND AND OBJECTIVES

Acute renal impairment is observed in 11%-23% of patients with congenital thrombotic thrombocytopenic purpura (TTP) and deficiency of a disintegrin and metalloprotease with thrombospondin motifs 13 (ADAMTS13, a metalloprotease that cleaves von Willebrand factor [VWF] multimers), a substantial percentage of whom develop CKD during follow-up.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Here we investigated whether, in 18 patients with congenital recruited from 1996 to 2013 who fulfilled inclusion criteria, acute renal involvement occurred during bouts segregated with lower secretion and activity levels of ADAMTS13 mutants. We performed expression studies and a sensitive recombinant VWF (rVWF) A1-A2-A3 cleavage test (detection limit, 0.78% of normal ADAMTS13 activity).

RESULTS

A higher risk of acute renal impairment during bouts was observed in patients with childhood (<18 years) onset (odds ratio [OR], 24.6 [95% confidence interval (CI), 1.11 to 542.44]) or a relapsing (≥1 episode per year) disease (OR, 54.6 [95% CI, 2.25 to 1326.28]) than in patients with adulthood onset or long-lasting remission, respectively. Whatever the age at onset, patients with acute renal impairment had mutations different from those in patients without renal involvement. Moreover, mutations in patients with acute renal impairment compared with those in patients without renal involvement caused lower in vitro rADAMTS13 secretion (1.33% versus 12.5%; P<0.001) and residual activity (0.11% versus 3.47%; P=0.003). rADAMTS13 secretion ≤3.75% and residual activity ≤0.4% best discriminated patients with renal impairment (receiver-operating characteristic curve sensitivity, 100% and 100%; specificity, 100% and 83.3%, respectively; logistic regression OR, 325 [95% CI, 6 to 18339] and 91.7 [95% CI, 3.2 to 2623.5], respectively). All mutations found in patients with childhood onset or relapsing disease were associated with acute renal impairment during bouts, confirming the link between acute renal impairment and early onset or a relapsing course. ADAMTS13 activity levels in vivo, measured in patients' serum by rVWF A1-A2-A3 cleavage test, correlated with in vitro rADAMTS13 mutant activity (r=0.95; P<0.001).

CONCLUSIONS

In congenital TTP, renal impairment and relapsing disease might be predicted by measurements of in vitro rADAMTS13 secretion and activity levels and in vivo serum ADAMTS13 activity.

Primary disease recurrence—effects on paediatric renal transplantation outcomes

Primary disease recurrence after renal transplantation is mainly diagnosed by examination of biopsy samples, but can also be associated with clinical symptoms. In some patients, recurrence can lead to graft loss (7-8% of all graft losses). Primary disease recurrence is generally associated with a high risk of graft loss in patients with focal segmental glomerulosclerosis, membranous proliferative glomerulonephritis, primary hyperoxaluria or atypical haemolytic uraemic syndrome. By contrast, disease recurrence is associated with a limited risk of graft loss in patients with IgA nephropathy, renal involvement associated with Henoch-Schönlein purpura, antineutrophil cytoplasmic antibody-associated glomerulonephritis or lupus nephritis. The presence of systemic diseases that affect the kidneys, such as sickle cell anaemia and diabetes mellitus, also increases the risk of delayed graft loss. This Review provides an overview of the epidemiology, pathophysiology and management of primary disease recurrence in paediatric renal graft recipients, and describes the overall effect on graft survival of each of the primary diseases listed above. With appropriate management, few paediatric patients should be excluded from renal transplantation programmes because of an increased risk of recurrence.

What's new in the diagnosis and pathophysiology of thrombotic thrombocytopenic purpura

Severe ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) deficiency causes thrombotic thrombocytopenic purpura (TTP), which is characterized by microangiopathic hemolytic anemia, thrombocytopenia, and the absence of oliguric or anuric renal failure. However, some patients with this constellation of findings do not have ADAMTS13 deficiency, and some patients with ADAMTS13 deficiency have renal failure or relatively normal blood counts. Consequently, many investigators and clinicians have incorporated severe ADAMTS13 deficiency into the case definition of TTP. This change has facilitated the timely initiation of treatment for patients with atypical clinical features who otherwise would not be recognized as having TTP. Conversely, excluding severe ADAMTS13 deficiency focuses attention on the diagnosis and treatment of other causes of thrombotic microangiopathy that require different treatment. The rapid return of ADAMTS13 data is important to make the best use of this information.

Successful treatment of relapsing autoimmune thrombotic thrombocytopenic purpura with rituximab

Thrombotic thrombocytopenic purpura (TTP) is a rare but life-threatening condition characterized by thrombotic microangiopathy. The standard treatment for TTP is plasmapheresis. For refractory or relapsing cases, various immunosuppressive agents have been tried, and among them rituximab has shown promising results. TTP is rarer in the pediatric age group and the use of rituximab in children with TTP is limited. Reported herein is the successful treatment of relapsing autoimmune TTP with rituximab in a 12-year-old girl.

ADAMTS-13 in the Diagnosis and Management of Thrombotic Microangiopathies

Thrombotic microangiopathies (TMAs) comprise a group of distinct disorders characterized by microangiopathic hemolytic anemia, thrombocytopenia, and microvascular thrombosis. For many years distinction between these TMAs, especially between thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS), remained purely clinical and hard to make. Recent discoveries shed light on different pathogenesis of TTP and HUS. Ultra-large von Willebrand factor (UL-VWF) platelet thrombi, resulting from the deficiency of cleavage protease which is now known as ADAMTS-13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13), were found to cause TTP pathology, while Shiga toxins or abnormalities in regulation of the complement system cause microangiopathy and thrombosis in HUS. TMAs may appear in various conditions such as pregnancy, inflammation, malignancy, or exposure to drugs. These conditions might cause acquired TTP, HUS, or other TMAs, or might be a trigger in individuals with genetic predisposition to ADAMTS-13 or complement factor H deficiency. Differentiation between these TMAs is highly important for urgent initiation of appropriate therapy. Measurement of ADAMTS-13 activity and anti-ADAMTS-13 antibody levels may advance this differentiation resulting in accurate diagnosis. Additionally, assessment of ADAMTS-13 levels can be a tool for monitoring treatment efficacy and relapse risk, allowing consideration of therapy addition or change. In the past few years, great improvements in ADAMTS-13 assays have been made, and tests with increased sensitivity, specificity, reproducibility, and shorter turnaround time are now available. These new assays enable ADAMTS-13 measurement in routine clinical diagnostic laboratories, which may ultimately result in improvement of TMA management.