Hereditary Thrombotic Thrombocytopenic Purpura Research Articles

Novel mechanisms of action of emerging therapies of hereditary thrombotic thrombocytopenic purpura.

Hereditary thrombotic thrombocytopenic purpura (hTTP) is caused by deficiency of plasma ADAMTS13 activity, resulting from ADAMTS13 mutations. ADAMTS13 cleaves ultra large von Willebrand factor (VWF), thus reducing its multimer sizes. Hereditary deficiency of plasma ADAMTS13 activity leads to the formation of excessive platelet-VWF aggregates in small arterioles and capillaries, resulting in hTTP. PubMed search from 1956-2024 using thrombotic thrombocytopenic purpura and therapy identified 3,675 articles. Only the articles relevant to the topic were selected for discussion, which focuses on pathophysiology, clinical presentations, and mechanisms of action of emerging therapeutics for hTTP. Current therapies include infusion of plasma, or coagulation factor VIII, or recombinant ADAMTS13. Emerging therapies include anti-VWF A1 aptamers or nanobody and gene therapies with adeno-associated viral vector or self-inactivated lentiviral vector or a Sleeping Beauty transposon system for a long-term expression of a functional ADAMTS13 enzyme. Frequent plasma infusion remains to be the standard of care in most parts of the world, while recombinant ADAMTS13 has become the treatment of choice for hTTP in some of the Western countries. The success of gene therapies in preclinical models may hold a promise for future development of these novel approaches for a cure of hTTP.

A rare case of hereditary thrombotic thrombocytopenic purpura in a toddler

A rare case of hereditary thrombotic thrombocytopenic purpura in a toddler

Importance of Prenatal Genetic Counselling: An Experience with Hereditary Thrombotic Thrombocytopenic Purpura

Importance of Prenatal Genetic Counselling: An Experience with Hereditary Thrombotic Thrombocytopenic Purpura

Thrombotic microangiopathy in children: Redefining hemolytic uremic syndrome, thrombotic thrombocytopenic purpura and related disorders

Thrombotic microangiopathy (TMA) is a triad of microangiopathic hemolytic anemia, thrombocytopenia, and end-organ ischemic damage. The primary mechanism involved is the occurrence of microthrombi due to deficient activity of ADAMTS13 (A Disintegrin And Metalloprotease with ThromboSpondin type 1 repeats, member 13). The most common types of TMA in children are Shiga toxin-producing Escherichia coli-associated hemolytic uremic syndrome (STEC-HUS) followed by complement-mediated (CM) TMA, Streptococcus pneumoniae-associated hemolytic uremic syndrome (Sp-HUS) and hereditary thrombotic thrombocytopenic purpura (hTTP) and other rare causes. Since the outcomes are dismal if appropriate treatment is not promptly initiated, there is a need to have a high clinical suspicion. Additionally, urgently performing ADAMTS13 functional activity and autoantibody levels can help differentiate hTTP, immune thrombotic thrombocytopenic purpura (iTTP), and CM-TMA. The etiological differentiation is crucial as eculizumab is a specific therapy with exceedingly good results in CM-TMA. While plasma exchanges are required for iTTP, besides corticosteroids and/or rituximab, plasma infusions suffice for hTTP. This review focuses on the commonly encountered congenital and acquired types of TMA in children and their varied presentations while briefly touching upon the rarer disorders causing TMA.

Value of Prophylactic Plasma Treatment and Incidence of Acute Episodes in Patients Enrolled in the International Hereditary Thrombotic Thrombocytopenic Purpura Registry

Background: Hereditary thrombotic thrombocytopenic purpura (hTTP), or Upshaw-Schulman syndrome, is a rare thrombotic microangiopathy due to a severe congenital deficiency of ADAMTS13 resulting from bi-allelic ADAMTS13 mutations. As in other plasma factor deficiencies, treatment consists of replacement of the missing ADAMTS13, which can currently be attempted with fresh frozen plasma, solvent/detergent plasma or plasma-derived factor VIII/Von Willebrand factor concentrates. Although prophylactic plasma infusions prevent acute episodes in many but not all hTTP patients, current treatment guidelines state conditional recommendations for prophylaxis outside of pregnancy, because evidence supporting the burdensome plasma prophylaxis in hTTP patients is scarce. Aims: Prospective evaluation of the incidence of acute episodes occurring in hTTP patients during periods with and without prophylactic plasma treatment. Methods: All patients with a confirmed diagnosis of hTTP enrolled in the International hTTP Registry between January 01, 2006 and December 31, 2021 were eligible for study. Diagnosis of hTTP was based on persisting ADAMTS13 activity <10%, bi-allelic ADAMTS13 mutations, and/or an infusion trial with full recovery and a half-life of plasma ADAMTS13 of around 60 hours. We recorded the patients' detailed medical history at enrollment and then collected prospective data on the clinical course, treatment modalities and laboratory values through site-visits and case report forms completed by treating physicians during annual visits or at occurrence of acute TTP episodes. Patients were followed until December 31, 2022 (database lock), death, or loss to follow-up, whatever came first. This post-hoc analysis evaluated acute TTP episodes during follow-up, stratified by periods on prophylaxis and without prophylaxis. Patients could contribute follow-up time to both periods (strata), but never simultaneously and gestation periods were excluded. Minimum criterion for long-term prophylaxis was defined as at least one monthly plasma infusion over a period of ≥ 6 months. Results were reported using descriptive statistics without formal statistical comparison and incident rates of acute TTP events were calculated per 1000 person-years with corresponding 95% confidence intervals (CIs). Results: At the end of December 2021, the International hTTP Registry had 182 confirmed hTTP patients eligible for this analysis that were followed for a median period of 3.6 (range, 0-18.5) years. The gender distribution showed more female (n=98, 53.8%) than male (n= 84, 46.2%) patients enrolled, a disparity likely related to a surge of diagnosis in women due to pregnancy complications. During prospective follow-up, 47 (25.8%) hTTP patients never had prophylactic treatment, while 135 (74.2%) received any form of prophylactic treatment, including long-term prophylaxis in 117 (86.7%). Patients who received any prophylactic treatment during follow-up had an incidence rate (95% CI) of acute TTP episodes of 272.4 (230.8-319.3) per 1000 person-years while receiving prophylaxis and of 520.4 (401.6-663.3) per 1000 person-years during periods without prophylaxis (Table 1). In the patients on long-term prophylaxis, the incidence rate of acute TTP episodes was 267.1 (226.0-313.6) per 1000 person-years in periods with prophylaxis, and 879.6 (664.4-1142.2) per 1000 person-years without prophylaxis. Irrespective of treatment interval, about half of patients on prophylaxis had break-through events, with the highest incidence rate observed in the group of patients receiving plasma products weekly, possibly reflecting their more precarious or severe disease course. Conclusions: In this large hTTP patient cohort observed for five years on average, we confirm the incidence rate of acute events as reported by Tarasco et al. (Blood 2021;137;3563-75). Here, we demonstrate for the first time that hTTP patients with disease courses requiring prophylaxis benefit from this burdensome treatment, which was most evident in patients on long-term prophylaxis. Current treatment options are however insufficient to suppress residual disease activity leading to break-through events observed in half of the patients on prophylaxis. Novel therapies, such as recombinant ADAMTS13, with the potential of reaching higher plasma levels, will likely overcome limitations of current treatment options.

Insight into the Natural History of Hereditary Thrombotic Thrombocytopenic Purpura: Short- and Long-Term Outcomes in a Longitudinally Followed Large Patient Cohort of the International Hereditary TTP Registry

Background: Hereditary thrombotic thrombocytopenic purpura (hTTP), also known as Upshaw-Schulman syndrome, is an ultra-rare, thrombotic microangiopathy resulting from bi-allelic ADAMTS13 mutations and severe congenital ADAMTS13 deficiency. Clinical presentation includes thrombocytopenia, hemolytic anemia and symptoms of organ ischemia (primarily of brain, heart, gastrointestinal tract and kidneys) during acute episodes and pregnancy complications, but less explicit symptoms (abdominal discomfort, headaches, neurocognitive problems or fatigue) responding to plasma therapy are also common. Standard of care consists of replenishing ADAMTS13 using plasma/plasma-derived blood products to treat acute episodes as well as prophylactically to prevent morbidity and mortality. Improvement of hTTP disease management requires better understanding of the treatment burden and possible shortcomings as well as short- and long-term clinical outcomes. Aims: Description of the natural history of hTTP in a prospectively followed large patient cohort with a focus on demographic and clinical characteristics, as well as on the occurrence of acute TTP episodes, comorbidities and mortality. Methods: Eligible for the current study were patients with a confirmed hTTP diagnosis (lasting ADAMTS13 activity <10%, bi-allelic ADAMTS13 mutations, and exclusion of acquired, autoimmune TTP) enrolled before December 31, 2021. In an ambidirectional approach, the registry assesses the patients' detailed medical history at enrollment (retrospective data) and then prospective clinical, molecular and observational data through questionnaires completed by treating physicians during annual visits or at occurrence of acute TTP episodes. Patients were followed by the International hTTP Registry until December 31, 2022 (end of current analysis), death, or loss to follow-up, whichever occurred first and results were reported using descriptive statistics. Results: At the end of December 2021, the International hTTP Registry had enrolled 182 confirmed hTTP patients from 49 sites in 20 countries, who were followed for a median of 3.6 (range, 0-18.5) years. The cohort included more female (n=98, 53.8%) than male (n= 84, 46.2%) patients, a gender disparity observed in adult patients because of increased diagnosis in women related to pregnancy complications. The patients were mostly White/Caucasian (n=111, 61.0%), followed by Asian (n=50, 27.5%), Black (n=2, 1.1%) and other ethnicities (n=19, 10.4%). Although 46.2% of the patients reported first symptoms of hTTP in the perinatal period (0-3 months), the median ages (ranges) at diagnosis and registry enrollment were 19.1 (0-69.9), and 30.4 (0.1-75) years, respectively. Prior to enrollment, 85.7% of patients had experienced at least one acute TTP episode with a mean (SD) of 4.3 (4.5) reported events per patient. The medical history was notable for transient ischemic attacks or strokes in 31% of hTTP patients, followed by arterial hypertension in 20%, chronic kidney disease in 12%, migraines/severe headaches in 8.2%, and seizures in 7.7%, respectively. During prospective follow-up 82 of 182 patients (45.1%) experienced 265 acute TTP episodes resulting in an overall event rate of 296.7 (95% confidence interval [CI]: 262.0-334.6) per 1000 person-years. Eight hTTP patients died during follow-up, five of them were on regular plasma prophylaxis. The causes of death were acute TTP episodes associated with cerebral (n=3; patient ages 33, 44 and 52 years) or cardiac (n=3; 39, 49, and 56 years) events, and unknown in two patients (75 and 79 years). Conclusions: The clinical burden due to recurrent acute TTP episodes and resulting neurological, cardiovascular and renal sequelae and other comorbidities is significant. Delayed diagnosis and insufficient treatment likely contributed to the observed morbidity and early mortality. Awareness, timely diagnosis and sufficient ADAMTS13 replacement therapy (for acute episodes and prophylactically) are crucial for improving short- and long-term clinical outcomes and disease burden in hTTP.

Evaluating the Impact of Hereditary Thrombotic Thrombocytopenic Purpura (hTTP) on Patients: A Patient Reported Outcomes (PROs) Study

Introduction: Hereditary thrombotic thrombocytopenic purpura (hTTP) is a rare inherited blood disorder caused by severe ADAMTS13 deficiency. There is a gender disparity with an increased incidence among women who are often diagnosed during pregnancy. Disease severity is variable with some patients requiring lifelong prophylaxis treatment while others require minimal or no treatment. Very little is known about the long-term impact of hTTP on psychological health, cognitive health and the quality of life of patients. In our previous study, patients frequently described neuropsychiatric symptoms such as depression, forgetfulness, and poor concentration (Borogovac, Blood 2022; 140:785-789). The goals of this study were to compare patient reported outcomes (PROs) between hTTP patients and the general population, compare hTTP to other disorders, and describe changes in these scores over time. Methods: hTTP patients were recruited from the United States (US) site of the international hTTP Registry. Following informed consent, PROMIS (Patient-Reported Outcomes Measurement Information System) fatigue, depression, anxiety, cognitive function, and positive affect/well-being measures were sent to patients via a secure REDCap link. Patients were assessed twice (baseline and 6-months). A one sample t-test compared mean scores in hTTP patients to the US population (mean 50, standard deviation 10). A paired t-test compared mean scores between the baseline and 6-month assessment. A literature search identified comparison disorders that reported PROMIS results. Descriptively, means and 95% confidence intervals (CI) were compared between hTTP and the other disorders. Results: Nineteen patients (16 adult; 3 pediatric) completed the baseline assessment. Their median age was 38 years (range 5 to 66 years), the majority were female (68.4%), had private insurance (63.2%) and lived near their hematologist (63.2% within 25 miles). Fifteen patients completed measures at both time points (baseline and 6-months). At baseline, hTTP patients were significantly worse than the US population on four domains of health: fatigue (p=0.0063), depression (p=0.02), anxiety (p=0.01), and cognitive function (p=0.02) (Figure 1). However, hTTP patient scores were not different from the US population for the domain of positive affect/well-being (p=0.78) (Figure 1). hTTP patients had similar PROMIS scores as patients with immune-mediated TTP, systemic lupus erythematosus, and rheumatoid arthritis (Table 1). However, hTTP patients had worse fatigue, depression, and anxiety than patients with hemophilia (Table 1). Among the 15 patients who completed both the baseline and 6-month assessments, there was no change in the mean fatigue (p=0.90), depression (p=0.29), anxiety (p=0.81), or cognitive function (p=0.89) scores. Conclusion: This is the first study to identify the impact of hTTP from the patient's perspective. Our results show that hTTP patients have significantly worse fatigue, depression, anxiety, and cognitive function than the US population with scores similar to patients with other chronic autoimmune disorders. However, hTTP patients had worse fatigue, depression, and anxiety than hemophilia patients which is a comparable genetic disorder. hTTP patients' scores did not improve over time which shows this disease has a persistent burden on patients. In future studies, it will be vital to incorporate the patient perspective to better understand the burden of both the disease and the treatment within this population. This approach will facilitate the development of new treatments that cater to patients' needs and preferences, ensuring a highly acceptable side effect profile and ultimately improving outcomes.

Hereditary Thrombotic Thrombocytopenic Purpura.

Hereditary thrombotic thrombocytopenic purpura (hTTP), also known as Upshaw-Schulman syndrome, is a rare genetic disorder caused by mutations in the ADAMTS13 gene that leads to decreased or absent production of the plasma von Willebrand factor (VWF)-cleaving metalloprotease ADAMTS13. The result is circulating ultra-large multimers of VWF that can cause microthrombi, intravascular occlusion and organ damage, especially at times of turbulent circulation. Patients with hTTP may have many overt or clinically silent manifestations, and a high index of suspicion is required for diagnosis. For the treatment of hTTP, the goal is simply replacement of ADAMTS13. The primary treatment is prophylaxis with plasma infusions or plasma-derived factor VIII products, providing sufficient ADAMTS13 to prevent acute episodes. When acute episodes occur, prophylaxis is intensified. Recombinant ADAMTS13, which is near to approval, will immediately be the most effective and also the most convenient treatment. In this review, we discuss the possible clinical manifestations of this rare disease and the relevant differential diagnoses in different age groups. An extensive discussion on prophylaxis and treatment strategies is also presented. Unique real patient cases have been added to highlight critical aspects of hTTP manifestations, diagnosis and treatment.

The challenging follow-up of pregnancy in women with known thrombotic thrombocytopenic purpura: a single-center experience of a preemptive management protocol.

Although thrombotic thrombocytopenic purpura frequently affects women of childbearing age, there is no clear recommendation for the management of subsequent pregnancies in women with established thrombotic thrombocytopenic purpura. This single-center, retrospective, observational study included all women with hereditary thrombotic thrombocytopenic purpura or immune thrombotic thrombocytopenic purpura who had had at least one subsequent pregnancy after thrombotic thrombocytopenic purpura diagnosis between 2003 and 2022. The strategy comprised weekly surveillance of platelet count during pregnancy (and quarterly monitoring of ADAMTS13 activity) for women with immune thrombotic thrombocytopenic purpura, without any routine prophylactic treatment. In case of thrombocytopenia < 150,000/mm3 (with or without hemolysis relapse), women with hereditary thrombotic thrombocytopenic purpura systematically received plasma infusions twice weekly until platelet count normalized. A total of 13 patients were included (7 with hereditary thrombotic thrombocytopenic purpura and 6 with immune thrombotic thrombocytopenic purpura, with 20 planned pregnancies (11 and 9, respectively). All pregnancies resulted in live births, and all mothers survived.There was a marked improvement in pregnancy terms in the hereditary thrombotic thrombocytopenic purpura group compared to index pregnancies (37 [35;39] versus 31 [24;38] weeks, p = 0.037) and birth weights (3265 [3029;3410] versus 2160 [1240;2705] grams, p = 0.016), with need for plasma support mostly starting during the third trimester (5/7 patients, 7/11 pregnancies). A single hereditary thrombotic thrombocytopenic purpura relapse occurred, with rapid resolution after plasma support intensification. There were no relapses in the immune thrombotic thrombocytopenic purpura group, with ADAMTS13 activity systematically above 40% during all monitored pregnancies. These real-life data support the feasibility of a preemptive approach to pregnancy monitoring in women with known thrombotic thrombocytopenic purpura who undergo active surveillance within a multidisciplinary network.

OC 26.1 Transient Ischemic Attacks (TIAs) and Ischemic Strokes are Leading Events in Hereditary Thrombotic Thrombocytopenic Purpura (hTTP)

OC 26.1 Transient Ischemic Attacks (TIAs) and Ischemic Strokes are Leading Events in Hereditary Thrombotic Thrombocytopenic Purpura (hTTP)

PB0332 Hereditary Thrombotic Thrombocytopenic Purpura: A Survey of Canadian Treaters

PB0332 Hereditary Thrombotic Thrombocytopenic Purpura: A Survey of Canadian Treaters

A Novel Variant on the Thrombospondin Type-1 Repeat 2 Domain of ADAMTS13 in a Parturient with Suspected Hereditary Thrombotic Thrombocytopenic Purpura and Unusually High ADAMTS13 Activity.

A Novel Variant on the Thrombospondin Type-1 Repeat 2 Domain of ADAMTS13 in a Parturient with Suspected Hereditary Thrombotic Thrombocytopenic Purpura and Unusually High ADAMTS13 Activity.

Immune and Hereditary Thrombotic Thrombocytopenic Purpura: Can ADAMTS13 Deficiency Alone Explain the Different Clinical Phenotypes?

Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy caused by a hereditary or immune-mediated deficiency of the enzyme ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13). TTPs are caused by the following pathophysiological mechanisms: (1) the presence of inhibitory autoantibodies against ADAMTS13; and (2) hereditary mutations of the ADAMTS13 gene, which is present on chromosome 9. In both syndromes, TTP results from a severe deficiency of ADAMTS13, which is responsible for the impaired proteolytic processing of high-molecular-weight von Willebrand factor (HMW-VWF) multimers, which avidly interact with platelets and subendothelial collagen and promote tissue and multiorgan ischemia. Although the acute presentation of the occurring symptoms in acquired and hereditary TTPs is similar (microangiopathic hemolytic anemia, thrombocytopenia, and variable ischemic end-organ injury), their intensity, incidence, and precipitating factors are different, although, in both forms, a severe ADAMTS13 deficiency characterizes their physiopathology. This review is aimed at exploring the possible factors responsible for the different clinical and pathological features occurring in hereditary and immune-mediated TTPs.

Expert consensus on diagnosis and treatment of hereditary thrombotic thrombocytopenic purpura in children

儿童遗传性血栓性血小板减少性紫癜（hTTP）是一种少见但严重，甚至可致命的儿童血栓性微血管病，其发病机制为血管性血友病因子裂解酶（ADAMTS13）基因突变所导致的ADAMTS13活性持续严重缺乏。相较于成人，儿童期起病的hTTP更易出现脑或肾远期并发症，对预防性替代治疗的需求更迫切。本共识涵盖hTTP的定义、诊断、鉴别诊断及治疗，旨在为中国儿科医师开展儿童hTTP规范化诊治提供参考。.

Von Willebrand factor antigen: a biomarker for severe pregnancy complications in women with hereditary thrombotic thrombocytopenic purpura?

BackgroundHereditary thrombotic thrombocytopenic purpura (hTTP) is associated with severe obstetric morbidity (SOM) during pregnancy. Treatment with fresh frozen plasma (FFP) mitigates the risk in some women, but others respond poorly and continue to suffer obstetric complications. ObjectivesTo determine a possible association between SOM and elevated nonpregnant von Willebrand factor (NPVWF) antigen levels in women with hTTP and whether the latter can predict the response to FFP transfusion. MethodsThis was a cohort-based study of women with hTTP due to homozygous c.3772delA mutation of ADAMTS-13 who had pregnancies both with and without FFP treatment. Occurrences of SOM were determined from medical records. Generalized estimated equation logistic regressions and receiver operating characteristic curve analysis determined the NPVWF antigen levels associated with the development of SOM. ResultsFourteen women with hTTP had 71 pregnancies; of which 17 (24%) culminated in pregnancy loss and 32 (45%) were complicated by SOM. FFP transfusions were administered in 32 (45%) of the pregnancies. Treated women had decreased SOM (28% vs 72%, p < .001) and preterm thrombotic thrombocytopenic purpura exacerbations (18% vs 82%, p < .001) and higher median NPVWF antigen levels than those of women with uncomplicated pregnancies (p = .018). Among the treated women, median NPVWF antigen levels were higher in those with SOM than in those without SOM (225% vs 165%, p = .047). Logistic regression models demonstrated a significant 2-way association between elevated NPVWF antigen levels (for SOM, odds ratio, 1.08; 95% CI, 1.001-1.165; p = .046) and SOM (for elevated NPVWF antigen levels, odds ratio, 1.6; 95% CI, 1.329-1.925; p < .001). The receiver operating characteristic curve analysis demonstrated that an NPVWF antigen level of 195% had 75% sensitivity and 72% specificity for SOM. ConclusionElevated NPVWF antigen levels are associated with SOM in women with hTTP. Women with levels >195% may benefit from increased surveillance and more intensive FFP treatment during pregnancy.

Frontiers in pathophysiology and management of thrombotic thrombocytopenic purpura.

Thrombotic thrombocytopenic purpura (TTP) is a fatal disease in which platelet-rich microthrombi cause end-organ ischemia and damage. TTP is caused by markedly reduced ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) activity. Hereditary or congenital TTP (cTTP) is caused by ADAMTS13 gene mutations. In acquired or immune TTP (iTTP), ADAMTS13 activity is reduced by anti-ADAMTS13 autoantibodies. TTP is characterized by thrombocytopenia, hemolytic anemia, fever, renal dysfunction, and neuropsychiatric symptoms. Therapeutic plasma exchange (TPE) and immunosuppressive therapy are the mainstays of treatment. As untreated TTP has a high mortality rate, immediate initiation of TPE is recommended when TTP is suspected. Conventionally, corticosteroids have been used for immunosuppressive therapy. Current drug therapies include rituximab, an anti-CD20 antibody that is effective in newly diagnosed cases and refractory cases, as well as for relapse prevention, and caplacizumab, an anti- von Willebrand factor (VWF) nanobody that inhibits the binding of platelets to VWF and prevents microthrombi formation. Recombinant human ADAMTS13 is a promising treatment for cTTP. Although these therapeutic advances have improved the outcomes of TTP, early diagnosis and prompt initiation of appropriate therapy are necessary to achieve these outcomes.

Recombinant ADAMTS13 for Hereditary Thrombotic Thrombocytopenic Purpura

SummaryA 27-year-old patient with a history of severe obstetrical complications and arterial thrombosis received a diagnosis of hereditary thrombotic thrombocytopenic purpura (TTP) due to severe ADAMTS13 deficiency when she presented with an acute episode in the 30th week of her second pregnancy. When the acute episode of hereditary TTP became plasma-refractory and fetal death was imminent, weekly injections of recombinant ADAMTS13 at a dose of 40 U per kilogram of body weight were initiated. The patient’s platelet count normalized, and the growth of the fetus stabilized. At 37 weeks 1 day of gestation, a small-for-gestational-age boy was delivered by cesarean section. At the time of this report, the patient and her son were well, and she continued to receive injections of recombinant ADAMTS13 every 2 weeks. (Funded by the Swiss National Science Foundation.)

Neonatal Exchange Transfusion: When Should We Think about Hereditary Thrombotic Thrombocytopenic Purpura (hTTP)?

Introduction Neonatal exchange transfusion (NExT) is a procedure to treat severe neonatal hyperbilirubinemia persisting despite phototherapy, to remove red cell allo-antibodies associated with excessive neonatal hemolysis and to correct severe anemia. During the past decades, the number of NExT preformed have steadily decreased, particularly since the introduction of rhesus prophylaxis in rhesus negative women. Hereditary thrombotic thrombocytopenic purpura (hTTP) because of severe congenital ADAMTS13 deficiency is a rare, autosomal recessively inherited disorder with an estimated prevalence of one case per million. Although excessive neonatal hemolysis (often in conjunction with thrombocytopenia) seems to be prevalent in hTTP, patients are seldom diagnosed with hTTP in the neonatal period, possibly because hTTP is not recognized as a differential diagnosis of severe neonatal hyperbilirubinemia and NExT. In this study, we investigated the prevalence of severe neonatal hyperbilirubinemia necessitating NExT among confirmed hTTP patients enrolled in the International Hereditary TTP Registry (www.ttpregistry.net; ClinicalTrials.gov Identifier: NCT01257269), at participating sites and in the literature in the past 20 years. Methods The International Hereditary TTP Registry is a cohort study for patients with confirmed hTTP and their family members, established in 2006. The hTTP Registry collects clinical and treatment information, as well as laboratory parameters retrospectively up to enrollment (including performance of NExT), and then prospectively during annual follow-up visits. Participating study sites and/or national coordinating centers were asked to provide information on the number of and indication for all NExT performed between January 2001 and July 2022. Finally, we performed a literature search to identify reports on NExT / neonatal exchange blood transfusion over the same 20-year period. Results At present, the International Hereditary TTP Registry has enrolled 178 confirmed hTTP patients. Forty-two (24%) of them had required NExT because of severe hyperbilirubinemia in the neonatal period, which led to early diagnosis of hTTP in 7/42 (16%) cases. In the remaining 33 patients treated with NExT, hTTP diagnosis was established in infancy/early childhood (between 3 months - ≤6 years of age) in 20 patients, and in 15 instances after 6 years of age. Of the 136 hTTP patients not requiring NExT, 35 (26%) had a disease onset in the neonatal period although only four of them (11%) were diagnosed at this time, while the majority (20/35 patients, 57%) received their hTTP diagnosis following further acute episodes in late adolescence or adulthood. Twelve of the 20 sites or national coordination centers participating in the International Hereditary TTP Registry answered our survey and reported 70 neonates treated with NExT over a period of 20 years. Indication for NExT were severe hyperbilirubinemia and or severe anemia due to AB0 or Rhesus incompatibility. In none of the cases hTTP was suspected or diagnosed, as immune-hematological findings indicated severe allo-antibody mediated hemolysis. We retrieved from PubMed 887 publications mentioning NExT or neonatal exchange blood transfusion, of which we excluded 229 papers, that did not describe patients treated with exchange transfusions. In the remaining 658 publications, patients were treated with exchange transfusions because of severe hyperbilirubinemia due to AB0-, Rhesus- or minor blood group incompatibilities, glucose-6-phosphate deficiency, sickle cell disease and severe infections. Only three publications mentioned the indication TTP. Conclusions Despite increased awareness and tools to diagnose hTTP, prompt recognition and diagnosis remain a critical impediment and result in delayed diagnosis and treatment. Early and persistent severe hyperbilirubinemia (often in conjunction with thrombocytopenia) necessitating NExT prevalent in newborns later in life diagnosed with hTTP. Differential diagnosis of severe neonatal hyperbilirubinemia should include hTTP and we suggest to determine ADAMTS13 activity together with molecular analysis of the ADAMTS13 gene in case of an ADAMTS13 activity <10% in any newborn requiring NExT for severe hyperbilirubinemia.

Coagulation Factor VIII Enhances the Cleavage of Von Willebrand Factor By ADAMTS13 In Vivo

Introduction: Coagulation factor VIII (FVIII) and von Willebrand factor (VWF) circulate as a noncovalent complex. This interaction helps increase the half-life of circulating FVIII and modulates FVIII immunogenicity. Our previous studies demonstrate that FVIII accelerates VWF proteolysis by ADAMTS13 in vitro under fluidic shear or under certain pathophysiological conditions. However, the physiological relevance of the FVIII-enhanced VWF proteolysis remains questionable. Here, we sought to determine if addition of recombinant FVIII at various concentrations to mice with or without circulating ADAMTS13 or to patients with hereditary thrombotic thrombocytopenic purpura (TTP) affects plasma VWF multimer distribution and its antigen levels. Methods: Recombinant human B-domain deleted FVIII (rFVIII) was intravenously administered into wild-type (WT),Adamts13+/-(A13+/-) and Adamts13-/- (A13-/-) mice. Blood samples were collected prior to and 24 hours following rFVIII infusion. In addition, FVIII was stably expressed in fviii-/-mice via administration of AAV8-BDDFVIII. Moreover, plasma was collected from patients with hereditary TTP who were treated with plasma derived FVIII concentrates. Plasma VWF multimers and antigen levels were determined by SDS-agarose gel electrophoresis followed by Western blotting and enzyme-linked immunoassay (ELISA), respectively. Paired T and Mann Whitney tests were performed to determine the statistical significance of the difference between two groups. Results: Our results demonstrated that an infusion of rFVIII at a low dose (40 ug/kg) and a high dose (160 ug/kg) into WT mice resulted in a dramatic reduction in plasma VWF multimer sizes (Fig. 1) and VWF antigen levels (not shown). FVIII at high dose but not at low dose could also significantly reduce the sizes of VWF multimers in Adamts13+/- and Adamts13-/- mice (Fig. 1). The enhanced degradation of VWF multimers in Adamts13-/- mice suggests that other VWF-cleaving enzymes may participate in the degradation of VWF-FVIII complex. In either Adamts13+/- or Adamts13-/- mice, administration of rFVIII at both low and high doses didn't result in significant changes in VWF antigen levels (not shown). Furthermore, a simultaneous infusion of both rFVIII and recombinant murine ADAMTS13 (rADAMTS13) into Adamts13-/- mice resulted in similar changes in plasma VWF multimer distribution (Fig. 1) and antigen levels (not shown). Importantly, all mice tolerated well to the high dose of rFVIII infusion without major thrombotic events during weeks of follow-up. The restoration of plasma FVIII to 100-200% of normal levels in the fviii-/- mice with AAV8-mediated gene therapy also led to a profound degradation of plasma VWF multimers and significantly reduced plasma levels of VWF antigen (not shown). Finally, a similar pattern of dramatically reduced plasma VWF multimers was observed in 3 out of 4 patients with hereditary TTP following treatment with plasma-derived FVIII concentrates (not shown). Conclusions: Our results demonstrate that supplementation of FVIII at physiological or super-physiological concentrations dramatically accelerates the degradation of VWF multimers in mice and human. These findings further support our hypothesis that FVIII is a physiological cofactor of ADAMTS13 in regulating VWF homeostasis. Our findings may also offer a scientific explanation how FVIII concentrates or perhaps rFVIII might work for the treatment of hereditary TTP and other arterial thrombosis. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Levels and Activity of Von Willebrand Factor in Patients with Hereditary Thrombotic Thrombocytopenic Purpura

Background: Mutations in the ADAMTS-13 gene in patients with hereditary thrombotic thrombocytopenic purpura interfere with production or function of ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) enzyme and increase levels of highly active large von Willebrand factor (vWF) multimers. Recent data from a cohort of hTTP patients carrying cDNA.4477_4477delA mutation in ADAMTS-13 gene suggested a discrepancy between ADAMTS13 activity and severity of clinical presentation. We proposed that the levels and activity of vWF might be elevated and associated with disease severity. In the present study we evaluated the levels and activity of vWF from homozygous cDNA.4477_4477delA mutation carriers in comparison to an historical cohort. Methods: In this retrospective cohort study all patients were diagnosed and treated at Soroka University Medical Center, Beer Sheba, Israel. Diagnosis of hTTP was confirmed by abnormal low levels of ADAMTS13, lack of anti-ADAMTS13 antibodies and positive testing for cDNA.4477_4477delA mutation. Patients' data were collected prospectively, while pre-enrollment data were collected retrospectively from the hospital records. The tests for von Willebrand factor activity (vWF:RCof) and von Willebrand factor antigen (vWF:Ag) were performed on non-pregnant patients and before FFP transfusions were initiated. Patients' vWF:RCof and vWF:Ag levels were compared to the values from previously published data of healthy subjects (Kilercik et al, Biological variations of ADAMTS13 and von Willebrand factor in human adults, Biochem. Medica. 24 [2014] 138-145). The data were analyzed using descriptive variables. vWF:RCof and vWF:Ag levels were compared using Mann-Whitney test. Results: Study population included 18 adults (15 female and three male patients) from two related families, all homozygous for c.3772 delA mutation. The age at initial presentation ranged from 18 to 48 years (mean 28.7±8.8). 17 patients were identified through episodes of microangiopathic hemolytic anemia (MAHA), thrombocytopenia, vascular and pregnancy complications (see Figure 1B). One subject was detected due to family history as part of family screening. Symptomatic patients received FFP transfusions every two weeks. Pregnant patients received FFP transfusions at a dose of two units every two weeks until the week 20 and thereafter two units weekly until delivery. All patients responded well to FFP transfusions. We did not observe hTTP-related mortality among study participants. Figure 1A shows the comparison with an historic control group. The control group had similar size (19 vs. 18 subjects in the study group). The patients in our study group were slightly older and had a female predominance (83.3%), while the control group had 47% females and 53% males. All 18 patients in our cohort had blood group A, 15 (83%) have been Rh positive. 14 patients (82%, 12 females and two male) were thrombocytopenic on initial presentation (median, 28 x103/µL, interquartile range [IQR] 14 x103/µL - 144 x103/µL). 13 patients (73%) were anemic (median hemoglobin 10.2 gr/dL, IQR 7.6 gr/dL - 10.9 gr/dL). Lactate dehydrogenase (LDH) (median, 1425 U/L, IQR 915 U/L - 1912 U/L) was elevated in 16 patients (89%) during initial presentation. Seven patients (39%) had a schistocyte count ≥1% on peripheral blood smear. Values of vWF antigen (vWF:Ag) (median 209.3% [range 141.5-240.5%] vs. 104% [range 86-116%], p value <0.001) and vWF activity (vWF:RCof) (median 130.6% [range 102.6-139%] vs. 83% [range 77-99%], P value <0.001) were significantly higher in the study group than in healthy controls, respectively (Figure 1A, 1C). Conclusions: Our results demonstrate that the levels of vWF antigen and activity in patients with hTTP are significantly higher than in healthy controls. These findings prompt further evaluation of vWF as a possible biomarker for the severity of hTTP. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal