Immunochip analysis identifies novel susceptibility loci in the human leukocyte antigen region for acquired thrombotic thrombocytopenic purpura.

Essentials Genetic predisposition to acquired thrombotic thrombocytopenic purpura (aTTP) is mainly unknown. Genetic risk factors for aTTP were studied by Immunochip analysis and replication study. Human leukocyte antigen (HLA) variant rs6903608 conferred a 2.5-fold higher risk of developing aTTP. rs6903608 and HLA-DQB1*05:03 may explain most of the HLA association signal in aTTP. Click to hear Dr Cataland's presentation on acquired thrombotic thrombocytopenic purpura SUMMARY: Background Acquired thrombotic thrombocytopenic purpura (TTP) is a rare, life-threatening thrombotic microangiopathy associated with the development of autoantibodies against the von Willebrand factor-cleaving protease ADAMTS-13. Similarly to what has been found for other autoimmune disorders, there is evidence of a genetic contribution, including the association of the human leukocyte antigen (HLA) class II complex with disease risk. Objective To identify novel genetic risk factors in acquired TTP. Patients/Methods We undertook a case-control genetic association study in 190 European-origin TTP patients and 1255 Italian healthy controls by using the Illumina Immunochip. Replication analysis in 88 Italian cases and 456 controls was performed with single-nucleotide polymorphism (SNP) TaqMan assays. Results and conclusion We identified one common variant (rs6903608) located within the HLA class II locus that was independently associated with acquired TTP at genome-wide significance and conferred a 2.6-fold increased risk of developing a TTP episode (95% confidence interval [CI] 2.02-3.27, P = 1.64 × 10-14 ). We also found five non-HLA variants mapping to chromosomes 2, 6, 8 and X that were suggestively associated with the disease: rs9490550, rs115265285, rs5927472, rs7823314, and rs1334768 (nominal P-values ranging from 1.59 × 10-5 to 7.60 × 10-5 ). Replication analysis confirmed the association of HLA variant rs6903608 with acquired TTP (pooled P = 3.95 × 10-19 ). Imputation of classic HLA genes followed by stepwise conditional analysis revealed that the combination of rs6903608 and HLA-DQB1*05:03 may explain most of the HLA association signal in acquired TTP. Our results refined the association of the HLA class II locus with acquired TTP, confirming its importance in the etiology of this autoimmune disease.

Rare bleeding disorders - bleeding assessment tools, laboratory aspects and phenotype and therapy of FXI deficiency.

Rare bleeding disorders (RBDs) are inherited deficiencies of coagulation factors such as fibrinogen, factor (F) II, FV, FVII, combined FV+FVIII, FX, FXI and FXIII. These disorders usually have a low prevalence in the general population and constitute approximately 3-5% of all coagulation disorders. However, in some countries they may have the same prevalence as haemophilia B due to the practice of consanguineous marriage. The clinical picture of RBDs is highly variable and can vary markedly from mild to severe, making both diagnosis and optimal treatment quite challenging. This review focuses on: (i) the efforts to establish a bleeding assessment tool adequate to RBDs, (ii) the optimal management of patients affected with FXI deficiency and (iii) the correlation between clinical severity and laboratory diagnosis when determining the minimum coagulant activity required to prevent bleeding in each RBD.

Measurement and prevalence of circulating ADAMTS13-specific immune complexes in autoimmune thrombotic thrombocytopenic purpura.

BACKGROUND: The formation of ADAMTS13-specific circulating immune complexes (CICs) may be a pathophysiologic mechanism in autoimmune thrombotic thrombocytopenic purpura (TTP), but has not been systematically investigated. OBJECTIVES: (a) To develop an assay for ADAMTS13-specific CICs; (b) to evaluate their prevalence in autoimmune TTP; and (c) to assess their association with ADAMTS13-related measurements and clinical features in autoimmune TTP patients. PATIENTS/METHODS: We developed and validated an ELISA method for ADAMTS13-specific CICs. ADAMTS13-specific CICs were searched for in 55 patients with autoimmune TTP from the Milan TTP Registry (URL:http://www.ttpdatabase.org/) and 28 controls. The associations between ADAMTS13-specific CIC levels and ADAMTS13 activity, antigen, anti-ADAMTS13 IgGs and acute TTP clinical features were assessed by multivariate linear regression. RESULTS: Intra- and inter-assay coefficients of variation of the new test were 5.3 and 9.6%. In 36 patients with severe ADAMTS13 deficiency and anti-ADAMTS13 autoantibodies, the prevalence of ADAMTS13-specific CICs was 47% (n = 17; 95% confidence interval [CI], 32-63%). ADAMTS13-specific CICs were detected also in seven of 19 (37%; 95% CI, 19-59%) patients with reduced ADAMTS13 activity, but apparently negative anti-ADAMTS13 autoantibodies. ADAMTS13-specific CICs were not associated with ADAMTS13 activity, antigen or anti-ADAMTS13 IgGs. In patients with acute TTP, increasing levels of ADAMTS13-specific CICs were associated with a higher number of plasma-exchange procedures required to attain remission (per 0.1 increase in normalized OD values, beta, 2.9; 95% CI, -0.7 to 6.5). CONCLUSIONS: Approximately one to two-thirds of patients with autoimmune TTP display ADAMTS13-specific CICs. A thorough investigation of the prognostic relevance of ADAMTS13-specific CIC levels in autoimmune TTP is warranted.

Is a decrease of microparticles related to improvement of hemostasis after FVIII injection in hemophilia A patients treated on demand?

BACKGROUND: Microparticles (MPs) are small membrane vesicles (0.1-1 µm) released from various cells after activation and/or apoptosis. There are limited data about their role in hemophilia A. PATIENTS AND METHODS: Blood samples were taken before and 30 min after FVIII injection in 18 patients with severe hemophilia A treated on demand. Flow-cytometric determination of total MPs (TMPs) using lactadherin, platelet MPs (PMPs) (CD42a), endothelial MPs (EMPs) (CD144) and leukocyte MPs (LMPs) (CD45) was performed. The results were compared with data on endogenous thrombin potential (ETP), overall hemostatic potential (OHP), fibrin gel permeability and thrombin-activatable fibrinolysis inhibitor (TAFI). RESULTS AND CONCLUSIONS: TMPs and PMPs decreased after treatment (to 1015 ± 221 [SEM] and 602 ± 134 × 10(6)  L(-1) ) in comparison with values before treatment (2373 ± 618 and 1316 ± 331; P < 0.01). EMPs also decreased after treatment (78 ± 12 vs. 107 ± 13; P < 0.05) while LMPs were not influenced. Both TMP and PMP counts were inversely correlated, moderately but statistically significantly, with data on OHP, ETP, fibrin network permeability and TAFI/TAFIi (P < 0.05 for all). EMP counts were correlated only with ETP (P < 0.05), while LMP counts did not show any correlation. TMP and PMP counts were also inversely correlated with FVIII levels (P < 0.05). TMP, PMP and EMP counts decreased after on-demand treatment with FVIII concentrate in hemophilia A patients. The decrease in circulating MPs, which were inversely correlated with hemostatic activation, may imply that MPs are incorporated in the hemostatic plug formed after FVIII substitution at the site of injury.

Coagulation factor activity and clinical bleeding severity in rare bleeding disorders: results from the European Network of Rare Bleeding Disorders.

BACKGROUND: The European Network of Rare Bleeding Disorders (EN-RBD) was established to bridge the gap between knowledge and practise in the care of patients with RBDs. OBJECTIVES: To explore the relationship between coagulation factor activity level and bleeding severity in patients with RBDs. PATIENTS/METHODS: Cross-sectional study using data from 489 patients registered in the EN-RBD. Coagulation factor activity levels were retrieved. Clinical bleeding episodes were classified into four categories according to severity. RESULTS: The mean age of patients at data collection was 31 years (range, 7 months to 95 years), with an equal sex distribution. On linear regression analysis, there was a strong association between coagulation factor activity level and clinical bleeding severity for fibrinogen, factor (F) X, FXIII, and combined FV and FVIII deficiencies. A weaker association was present for FV and FVII deficiencies. There was no association between coagulation factor activity level and clinical bleeding severity for FXI. The coagulation factor activity levels that were necessary for patients to remain asymptomatic were: fibrinogen, > 100 mg dL(-1); FV, 12 U dL(-1); combined FV + VIII, 43 U dL(-1); FVII, 25 U dL(-1); FX, 56 U dL(-1) ; FXI, 26 U dL(-1); FXIII, 31 U dL(-1). Moreover, coagulation factor activity levels that corresponded with Grade III bleeding were: undetectable levels for fibrinogen, FV and FXIII, < 15 U dL(-1) for combined FV + VIII; < 8 U dL(-1) for FVI; < 10 U dL(-1) for FX; and < 25 U dL(-1) for FXI. CONCLUSIONS: There is a heterogeneous association between coagulation factor activity level and clinical bleeding severity in different RBDs. A strong association is only observed in fibrinogen, FX and FXIII deficiencies.

On-demand but not prophylactic treatment with FVIII concentrate increase thrombin activatable fibrinolysis inhibitor activation in severe haemophilia A patients.

INTRODUCTION: Thrombin activatable fibrinolysis inhibitor (TAFI) down-regulates fibrinolysis after activation by thrombin/thrombomodulin. We investigated the effect of treatment with FVIII concentrate on plasma levels of pro-TAFI and activated TAFI in haemophilia A patients. METHODS: Samples were collected pre and posttreatment from patients treated prophylactically or on-demand. Pro-TAFI, TAFI/TAFIi and FVIII levels were measured in all samples. RESULTS: Treatment had no effect on pro-TAFI levels. Pro-TAFI was similar in both patient groups but higher than in controls. Patients from the prophylactic treatment group had measurable FVIII levels pretreatment while in the treatment-on-demand group FVIII levels were ≤0.01 IU/mL. In the prophylactic treatment group, the levels of TAFI/TAFIi were significantly lower pre- and posttreatment (4.31 ± 3.14 and 3.48 ± 2.65 ng/mL respectively) than in the on-demand group (13.02 ± 3.47 and 14.87 ± 3.47 ng/mL respectively). This difference may be due to release of tissue factor at the injury site in the on-demand group. This could induce thrombin and TAFI activation within the clot counterbalancing fibrinolysis in these patients. In the prophylactic group, no injury existed, thus there was insufficient thrombin generation within the clot to activate TAFI. CONCLUSION: These findings suggest that in patients to whom FVIII is administered on demand the fibrinolysis activity is more down regulated than in patients following a prophylactic treatment regime.

Central nervous system bleeding in patients with rare bleeding disorders.

Central nervous system (CNS) bleeding is one of the most severe and debilitating manifestations occurring in patients with rare bleeding disorders (RBDs). The aim of this study was to retrospectively collect data on patients affected with RBDs who had CNS bleeding, to establish incidence of recurrence, death rate, neurological sequences, most frequent location, type of bleeding and efficacy of treatments. Results pertained to 36 CNS bleeding episodes in 24 patients with severe deficiency except one with moderate factor VII (FVII) deficiency. Six patients (25%) experienced a recurrence and two had more than one recurrence. Seven patients (29%) had an early onset of CNS bleeding before the first 2 years of life, others (71%) later in life. In 76% of cases, CNS bleeding was spontaneous. CNS bleeding was intracerebral in 19 cases (53%), extracerebral in 10 (28%) and both intracerebral and extracerebral in two cases (6%). Neurosurgery was performed in 11 cases, in association with replacement therapy in seven cases. Seizures were noted in four patients. Residual psychomotor abnormalities were seen in two patients. No death was recorded. To prevent recurrence, 17/24 patients (71%) were put on secondary prophylaxis. In conclusion, recurrence of CNS bleeding was confirmed to be relatively frequent in patients with severe FV, FX, FVII and FXIII deficiencies. Most patients were managed with replacement therapy alone, surgery being reserved for those with worsening neurological conditions. Our results indicate that some RBDs require early prophylactic treatment to prevent CNS bleeding. Optimal dosage and frequency of treatment need further evaluation.

[Lupus anticoagulant in pregnancy--first experiences in detection and therapy]. / Lupusni antikoagulans u trudnoci--prva iskustva u dijagnostici i terapiji.

We examined 62 women with three or more recurrent adverse pregnancy outcomes where we excluded the other well known causes of this state. We detected lupus anticoagulant (LAC) in three (5%), with the use of set of coagulation tests: activated partial thromboplastin time (APTT), APTT ratio, kaolin clotting time ratio (KCT), APTT of the 50:50 mixture of the patients and control plasmas, APTT ratio of the 50:50 mixture, phospholipid correction test and heat stability test. We excluded connective tissue disorders. Therapy was started between 12th and 14th gestational week. Efficacy was monitored in intervals of 2-6 weeks with following tests: APTT ratio, KCT and plateled count. Patient A, with strong LAC activity and thrombocytophenia, reacted weakly to therapy with Pronison 40 mg/day and Aspirin 80 mg/day. The activity of LAC was slightly diminished but was present all the time. Patient expressed hypertension and gestational diabetes mellitus. The outcome of pregnancy was adverse and placenta had typical pathological changes. Patient B, with moderate LAC activity, reacted quickly and completly on therapy with Pronison 20-40 mg/day and Aspirin 80 mg/day. The course of pregnancy was regular. The outcome was successful and placenta had no pathological changes. Patient C, with mild LAC activity, was treated only with Aspirin 80 mg/day. LAC activity rapidly disappeared, the course of pregnancy was regular and outcome was successful. On the basis of the first results we concluded that applied set of tests was sensitive for LAC of different intensity and that dissapeparance of LAC activity with the use of therapy anticipates successful pregnancy outcome.