A new method for characterization and epitope determination of a lupus anticoagulant-associated neutralizing antiprothrombin antibody

Lupus anticoagulant-hypoprothrombinemia syndrome in children: Three case reports and systematic review of the literature

OBJECTIVE

Children with lupus anticoagulant hypoprothrombinemia syndrome (LAHPS) are characterized by prolonged activated partial thromboplastin time (APTT) and prothrombin time (PT), lupus anticoagulant positivity and low prothrombin (factor II, FII) levels. Bleeding or thrombosis tendencies related to LAHPS in children can occur due to the development of anti-prothrombin antibodies that are usually linked to autoimmune or infectious diseases.

METHODS

We report three pediatric cases of LAHPS and describe details on their clinical symptoms, laboratory characteristics, treatment. PubMed, Medline, and Web of Science searches were conducted on LAHPS in children between 1960 and 2023; articles in English were included.

RESULTS

The coagulation profile revealed prolonged PT and APTT, with low prothrombin levels (19.4%, 21.0% and 12.9%, respectively) and positive lupus anticoagulant in 3 pediatric cases. Fifty-nine relevant articles reported 93 pediatric LAHPS cases (mean age: 9 years (0.8-17 years)); 63 females and 30 males, 87 patients presented with minor to severe bleeding diathesis, and 3 patients presented with thrombosis events. Among 48 patients ≥9 years old, 36 had SLE; among 45 patients <9 years, 29 had viral infection. When all patients were divided into two groups based on age, associated disease, and factor II level, Pearson's χ2 tests were performed, p =.00, and there was clinical significance between autoimmune and infectious disease in patients ≥9 years old and <9 years old, and in patients FII level ≤10% and >10%. LAHPS patients with autoimmune disease had a protracted course and needed prolonged treatment with immune-modulating therapy, while those patients with infectious disease resolved spontaneously or needed short-term immune-modulating therapy.

CONCLUSION

LAHPS caused by autoimmune disease are common in patients ≥9 years old, especially SLE, and FII level ≤10% is often reported in patients caused by autoimmune disease, suggesting that children ≥9 years old diagnosed with LAHPS-related autoimmune disease should pay special attention to the FII level. While LAHPS caused by infectious disease is more frequently observed in patients <9 years, especially viral infection. Early diagnostic investigations are critical to differentiating LAHPS caused by autoimmune or infectious disease, as the prognosis, treatment and outcome are distinct.

Discovery and characterization of 2 novel subpopulations of aPS/PT antibodies in patients at high risk of thrombosis

Anti-phosphatidylserine/prothrombin (aPS/PT) antibodies are often detected in patients with antiphospholipid syndrome (APS), but how aPS/PT engage prothrombin at the molecular level remains unknown. Here, the antigenic determinants of immunoglobulin G aPS/PT were investigated in 24 triple-positive APS patients at high risk of thrombosis by using prothrombin mutants biochemically trapped in closed and open conformations, and relevant fragments spanning the entire length of prothrombin. Two novel unexpected findings emerged from these studies. First, we discovered that some aPS/PT are unique among other anti-prothrombin antibodies insofar as they efficiently recognize prothrombin in solution after a conformational change requiring exposure of fragment-1 to the solvent. Second, we identified and characterized 2 previously unknown subpopulations of aPS/PT, namely type I and type II, which engage fragment-1 of prothrombin at different epitopes and with different mechanisms. Type I target a discontinuous density-dependent epitope, whereas type II engage the C-terminal portion of the Gla-domain, which remains available for binding even when prothrombin is bound to the phospholipids. Based on these findings, APS patients positive for aPS/PT were classified into 2 groups, group A and group B, according to their autoantibody profile. Group A contains mostly type I antibodies whereas group B contains both type I and type II antibodies. In conclusion, this study offers a first encouraging step toward unveiling the heterogeneity of anti-prothrombin antibodies in correlation with thrombosis, shedding new light on the mechanisms of antigen-autoantibody recognition in APS.

Lupus anticoagulant-hypoprothrombinemia syndrome and immunoglobulin-A vasculitis: a report of Japanese sibling cases and review of the literature

Lupus anticoagulant-hypoprothrombinemia syndrome (LAHPS) is a rare bleeding disorder caused by antiprothrombin antibodies. LAHPS is associated with systemic lupus erythematosus (SLE) or infections. We describe two Japanese brothers with immunoglobulin-A vasculitis (IgAV) who met the diagnostic criteria of LAHPS. They presented with palpable purpura and abdominal pain, and had a prolonged activated partial thromboplastin time (APTT) and prothrombin deficiency with the presence of lupus anticoagulant. Pediatric LAHPS was reviewed in abstracts from the Japan Medical Abstracts Society that were written in Japanese and PubMed or Web of Science-listed articles in English between 1996 and 2019. Including our cases, pediatric LAHPS has been reported in 40 Japanese and 46 non-Japanese patients. We summarized the clinical and laboratory characteristics of all 86 cases, and found only one Japanese LAHPS case with IgAV, except for our cases. Of the 86 cases, most were associated with infections followed by SLE. The presence of SLE, older age, lower prothrombin levels, severe bleeding symptoms, and positivity of immunoglobulin G anticardiolipin antibodies and anticardiolipin/β₂-glycoprotein I antibodies and/or β₂-glycoprotein I-dependent anticardiolipin antibodies had higher odds of requiring treatment. Measuring the APTT and prothrombin time (PT) might be required in patients with IgAV when they do not have a typical clinical course or distinctive symptoms. LAHPS should be considered with prolongation of the APTT and/or PT. Additionally, it is important to maintain a balance between the risk of thrombosis and hemorrhage when normalization of the PT and FII levels occurs in LAHPS cases under treatment.

Rituximab use in pediatric lupus anticoagulant hypoprothrombinemia syndrome - report of three cases and review of the literature

Lupus anticoagulant hypoprothrombinemia syndrome (LA-HPS) is a rare condition that may predispose both to thrombosis and bleeding due to positive lupus anticoagulant (LA) and factor II (FII) deficiency. It can be seen in association with infections or systemic lupus erythematosus (SLE) and may require glucocorticoids (GCs) and/or immunosuppressive medications. Pediatric LA-HPS cases in the literature and three cases that received only rituximab (RTX) for LA-HPS (in addition to GCs) at two institutions between January 2010 and June 2017 were analyzed descriptively. Pediatric LA-HPS cases (≤18 years) with bleeding or thrombotic events were included. Information obtained included demographics, presenting symptoms, diagnoses, treatments, pre-/post-treatment prothrombin time (PT)/partial thromboplastin time (PTT)/LA/FII levels, and outcomes. In addition to three LA-HPS cases identified at our institutions, as of June 2017, 37 articles reported 54 pediatric LA-HPS cases (mean age: 8 years (0.9-17 years); female/male: (2:1); viral illness 27 (50%), SLE 20 (37%), and other six (11%)). All cases had a positive LA and FII deficiency (range: 0%-40%). All cases presented with bleeding diathesis and were treated with various regimens, but there was no reported use of RTX. The purpose of this report is to describe the novel use of RTX as a steroid-sparing agent in three pediatric SLE cases and to systematically review the literature on pediatric cases of LA-HPS.

Lupus anticoagulant acquired hypoprothrombinemia syndrome in childhood: two distinct patterns and review of the literature

INTRODUCTION

Lupus anticoagulant associated with acquired prothrombin deficiency also known as 'lupus anticoagulant hypoprothrombinemia syndrome' (LAHS) is an entity that is well described in adults and is usually associated with autoimmune conditions (LAHS-AI). However, in children, LAHS has unique features that are distinct from the adult type.

AIMS

We report two paediatric cases of LAHS, describe their distinct patterns and review the paediatric literature on LAHS.

METHODS

Case studies on two patients with LAHS were reviewed, details on their presentation, work up and management were extracted. A Medline search was conducted on LAHS in children between 1960 and 2014; Articles in languages other than English were excluded.

RESULTS

The case studies highlight the differences in the two patterns of childhood LAHS. Additionally the review of the literature reveals that there are 15 case reports and 5 case series that report 25 children with LAHS-AI, 9 case reports and 6 case series report 26 children of LAHS associated with viral infections (LAHS-VI). At presentation, all patients with LAHS-AI had positive laboratory tests for autoimmune diseases, most commonly for systemic lupus erythematosus while these tests were negative in LAHS-VI. All patients with LAHS-AI had a protracted course and needed prolonged treatment with immune-suppressive therapy while patients with LAHS-VI resolved spontaneously or needed short-term immune-modulating therapy.

CONCLUSION

In childhood, two distinct patterns of LAHS are observed, either associated with infection or autoimmune disease. Initial diagnostic investigations are critical to differentiating these two patterns as the prognosis and outcome for each is distinct.

Lupus anticoagulant-hypoprothrombinemia syndrome: report of two cases and review of the literature

Lupus anticoagulant-hypoprothrombinemia syndrome (LA-HPS) is a rare acquired disorder caused by prothrombin antibodies. The disease is most common in the pediatric age group (<16 years), and more prevalent in women. There are well-established clinical diseases associated with LA-HPS, most notably systemic lupus erythematosus (SLE) and viral infections. The clinical manifestation of LA-HPS varies greatly in severity and it may cause severe life-threatening bleeding diathesis. LA-HPS is to be suspected when a patient presents with bleeding and a prolonged activated partial thromboplastin and prothrombin time, in combination with a lupus anticoagulant. The diagnosis is confirmed in the laboratory by identification of reduced prothrombin levels. There are no standardized recommendations for treatment of the hemorrhage associated with the syndrome; corticosteroids are used as first-line treatment. This review summarizes what is currently known about the pathogenesis, clinical features, diagnosis, treatment and prognosis of LA-HPS, and presents two case reports.

Lupus anticoagulant-hypoprothrombinemia syndrome: report of 8 cases and review of the literature

The lupus anticoagulant-hypoprothrombinemia syndrome (LAHS)--the association of acquired factor II deficiency and lupus anticoagulant--is a rare disease drastically different from antiphospholipid syndrome in that it may cause predisposition not only to thrombosis but also to severe bleeding. We performed a retrospective study of 8 patients with LAHS referred to 6 French tertiary care centers between January 2003 and February 2011, and a literature review retrieving all related articles published between 1960 and April 2011. Including our 8 new cases, LAHS has been reported in 74 cases. The disease mostly occurs in young adults, with a female to male sex ratio of 1.4. Associated conditions mostly include autoimmune diseases such as systemic lupus erythematosus and infectious diseases. Bleeding is a frequent feature (89% of cases), while arterial and/or venous thrombosis is less common (13%). Factor II level is severely decreased at diagnosis (median value, 11%; range, 1%-40%). LAHS associated with autoimmune diseases is more persistent than LAHS associated with infection, and hemorrhagic complications are more common. Corticosteroids should be considered the first-line treatment, but the thrombotic risk strongly increases during treatment because of the improvement of factor II level. Despite the fact that 50% of patients develop severe bleeding, the mortality rate is <5%, after a median follow-up of 13 months (range, 0.5-252 mo). LAHS associated with autoimmune diseases should be diagnosed and managed carefully because the disease is persistent and severe hemorrhagic complications are common.

Coeliac disease and hearing loss: preliminary data on a new possible association

OBJECTIVE

Coeliac disease (CD), an autoimmune gluten-dependent enteropathy, can be associated with several extra-intestinal manifestations, including neurological disorders. At present, no data are available on the presence of hearing loss disorder in coeliac patients. The aim of the present study was to investigate the prevalence of hearing loss in coeliac patients compared with that in healthy controls.

MATERIAL AND METHODS

Twenty-four adult coeliac patients and 24 healthy subjects matched for gender, age, smoking and drinking habits were enrolled in the study. Among the coeliac patients, 6 were newly diagnosed and 18 patients were on a gluten-free diet for at least one year.

RESULTS

A hearing loss was found in 10 (47.1%) coeliac patients and 2 (9.1%) healthy controls. All CD patients with hearing loss presented a sensorineural hearing loss. The prevalence of hearing loss was significantly higher in coeliac patients than in healthy controls (p = 0.01) but it was not significantly different between untreated (33.3%) and treated (44.4%) coeliac patients (p: NS).

CONCLUSIONS

Despite the low number of subjects evaluated, the present study showed a higher prevalence of hearing loss in coeliac patients than in healthy controls, suggesting an association between CD and hearing loss. Immunological processes such as ear-specific and non-specific autoantibodies and vasculitis could be the basis of this association. Further longitudinal investigations on a larger sample size will be necessary to confirm the present data.

Inhibition of thrombin activity by prothrombin activation fragment 1.2

Prothrombin is the precursor of thrombin, the central enzyme in coagulation. Prothrombin is activated in vivo by the prothrombinase complex to form fragment 1.2 and thrombin. Fragment 1.2 has an amino-terminal gla domain and two kringle domains. The second kringle domain (kringle 2) binds to the exosite II on thrombin. Nascent thrombin generated on platelet surface remains non-covalently bound to fragment 1.2 by kringle 2-exosite II interaction. To determine whether this interaction can modulate coagulant activity of thrombin, we labeled thrombin at the active site with fluorescein-Phe-Pro-Arg chloromethylketone and monitored the fluorescence changes upon ligand binding. Anionic phospholipid-bound fragment 1.2 and fragment 2 bound to FPR-thrombin and induced changes in the active site with half maximal effects at 7.2 microM and 8.8 microM, respectively. We also tested the effect of anionic phospholipid-bound fragment 1.2 (0-10 microM) on thrombin clotting activity. Phospholipid-bound fragment 1.2 inhibited fibrinogen clotting in a concentration-dependent manner but had no significant effect on amidolytic activity towards S2238, suggesting a competitive inhibition of the fibrinogen binding site. Furthermore, fragment 1.2 inhibited FPR-thrombin binding to platelet. Consistent with these findings fragment 1.2 inhibited thrombin-induced aggregation of gel filtered platelets in a concentration-dependant manner. These results suggest that the membrane-bound prothrombin fragment 1.2 may play a role in hemostasis by down regulating the procoagulant activity of newly formed thrombin.

Inhibition of prothrombin activation by bothrojaracin, a C-type lectin from Bothrops jararaca venom

Bothrojaracin is a potent and specific alpha-thrombin inhibitor (Kd approximately 0.6 nM) isolated from Bothrops jararaca venom. It binds to both of thrombin's anion-binding exosites (1 and 2), thus inhibiting the ability of the enzyme to act upon several natural macromolecular substrates, such as fibrinogen, platelet receptor, protein C, and factor V. Additionally, bothrojaracin interacts with prothrombin (Kd approximately 30 nM), as previously determined by a solid-phase assay. However, there is no information concerning the effect of this interaction on prothrombin activation and whether the binding of bothrojaracin can occur in plasma. Here, we show that bothrojaracin specifically interacts with prothrombin in human plasma. It is an effective anticoagulant after activation of the intrinsic pathway of blood coagulation, and analysis of prothrombin conversion in plasma shows that bothrojaracin strongly reduces alpha-thrombin formation. To determine whether this effect is due exclusively to inhibition of feedback reactions involving the thrombin-induced activation of factors V and VIII, we analyzed the effect of bothrojaracin on the activation of purified prothrombin by Oxyuranus scutellatus venom. As with plasma, bothrojaracin greatly inhibited thrombin formation, suggesting a direct interference in the prothrombin activation by the enzyme found in this venom (scuterin, a prothrombin activator described as a factor Xa/factor Va-like complex). Altogether, we suggest that bothrojaracin exerts its anticoagulant effect in plasma by two distinct mechanisms: (1) it binds generated thrombin and inhibits exosite 1 dependent activities such as fibrinogen clotting and factor V activation, and (2) it interacts with prothrombin and decreases its proteolytic activation. Thus, bothrojaracin may be useful in the search for thrombin inhibitors that bind both the zymogen and the active enzyme.