Pathophysiology of thrombotic thrombocytopenic purpura : the "two-hit" paradigm

Thrombotic thrombocytopenic purpura (TTP) is a rare, life-threatening disease characterized by acute episodes of widespread thrombosis in capillaries and small arteries. The discovery that the plasmatic activity of the von Willebrand factor cleaving protease, ADAMTS13, is severely deficient in patients with TTP represented a turning point in the understanding of the pathophysiology of the disease. In spite of recent advances, the clinical course of TTP is characterized by considerable heterogeneity, the causes of which are largely unknown. Herein, we present a number of studies investigating the determinants of clinical heterogeneity in patients with both congenital and acquired forms of TTP. A __two-hit__ model of the pathophysiology of TTP is presented.The support of Fondazione Luigi Villa, Milan (Italy), is gratefully acknowledgedUBL - phd migration 201

Prevalence of disease and relationships between laboratory phenotype and bleeding severity in platelet primary secretion defects

BACKGROUND: The prevalence of platelet primary secretion defects (PSD) among patients with bleeding diathesis is unknown. Moreover, there is paucity of data on the determinants of bleeding severity in PSD patients. OBJECTIVE: To determine the prevalence of PSD in patients with clinical bleeding and to study the relationships between the type of platelet defect and bleeding severity. METHODS: Data on patients referred for bleeding to the Angelo Bianchi Bonomi Hemophilia and Thrombosis Center, Milan (Italy) in the years between 2008 and 2012 were retrieved to study the prevalence of PSD. Demographic, clinical and laboratory information on 32 patients with a diagnosis of PSD was used to compare patients with or without associated medical conditions and to investigate whether or not the type and extension of platelet defects were associated with the bleeding severity score (crude and age-normalized) or with the age at first bleeding requiring medical attention. RESULTS: The estimated prevalence of PSD among 207 patients with bleeding diathesis and bleeding severity score above 4 was 18.8% (95% confidence interval [CI]: 14.1-24.7%). Patients without associated medical conditions had earlier age of first bleeding (18 vs 45 years; difference: -27 years; 95% CI: -46 to -9 years) and different platelet functional defect patterns (Fisher's exact test of the distribution of patterns, P\u200a=\u200a0.007) than patients with accompanying medical conditions. The type and extension of platelet defect was not associated with the severity of bleeding. CONCLUSIONS: PSD is found in approximately one fifth of patients with clinical bleeding. In patients with PSD, the type and extension of laboratory defect was not associated with bleeding severit

Pregnancy complications in acquired thrombotic thrombocytopenic purpura : a case-control study

BackgroundPregnant women with a history of acquired thrombotic thrombocytopenic purpura (TTP) are considered at risk for disease recurrence and might be at risk for miscarriage, similar to other autoimmune disorders. However, the exact entity of these risks and their causes are unknown. The aim of this study was to evaluate risk factors associated with adverse pregnancy outcome, in terms of both gravidic TTP and miscarriage, in women affected by previous acquired TTP.MethodsWe conducted a nested case\ubfcontrol study in women with a history of acquired TTP enrolled in the Milan TTP registry from 1994 to October 2012, with strict inclusion criteria to reduce referral and selection bias.ResultsFifteen out of 254 women with acquired TTP were included, namely four cases with gravidic TTP, five with miscarriage, and six controls with uncomplicated pregnancy. In the cases, ADAMTS13 activity levels in the first trimester were moderately-to-severely reduced (median levels <3% in gravidic TTP and median levels 20% [range 14-40%] in the women with miscarriage) and anti-ADAMTS13 antibodies were invariably present, while in the control group ADAMTS13 activity levels were normal (median 90%, range 40-129%), with absence of detectable anti-ADAMTS13 antibodies. Reduced levels of ADAMTS13 activity (<25%) in the first trimester were associated with an over 2.9-fold increased risk for gravidic TTP and with an over 1.2-fold increased risk for miscarriage (lower boundary of the confidence interval of the odds ratio). In addition, the presence of anti-ADAMTS13 antibodies during pregnancy was associated with an over 6.6-fold increased risk for gravidic TTP and with an over 4.1-fold increased risk for miscarriage.ConclusionsADAMTS13 activity evaluation and detection of anti-ADAMTS13 antibody could help to predict the risk of complications in pregnant women with a history of acquired TTP

Identification of genetic risk variants for deep vein thrombosis by multiplexed next-generation sequencing of 186 hemostatic/pro-inflammatory genes

BACKGROUND: Next-generation DNA sequencing is opening new avenues for genetic association studies in common diseases that, like deep vein thrombosis (DVT), have a strong genetic predisposition still largely unexplained by currently identified risk variants. In order to develop sequencing and analytical pipelines for the application of next-generation sequencing to complex diseases, we conducted a pilot study sequencing the coding area of 186 hemostatic/proinflammatory genes in 10 Italian cases of idiopathic DVT and 12 healthy controls. RESULTS: A molecular-barcoding strategy was used to multiplex DNA target capture and sequencing, while retaining individual sequence information. Genomic libraries with barcode sequence-tags were pooled (in pools of 8 or 16 samples) and enriched for target DNA sequences. Sequencing was performed on ABI SOLiD-4 platforms. We produced > 12 gigabases of raw sequence data to sequence at high coverage (average: 42X) the 700-kilobase target area in 22 individuals. A total of 1876 high-quality genetic variants were identified (1778 single nucleotide substitutions and 98 insertions/deletions). Annotation on databases of genetic variation and human disease mutations revealed several novel, potentially deleterious mutations. We tested 576 common variants in a case-control association analysis, carrying the top-5 associations over to replication in up to 719 DVT cases and 719 controls. We also conducted an analysis of the burden of nonsynonymous variants in coagulation factor and anticoagulant genes. We found an excess of rare missense mutations in anticoagulant genes in DVT cases compared to controls and an association for a missense polymorphism of FGA (rs6050; p = 1.9 7 10(-5), OR 1.45; 95% CI, 1.22-1.72; after replication in > 1400 individuals). CONCLUSIONS: We implemented a barcode-based strategy to efficiently multiplex sequencing of hundreds of candidate genes in several individuals. In the relatively small dataset of our pilot study we were able to identify bona fide associations with DVT. Our study illustrates the potential of next-generation sequencing for the discovery of genetic variation predisposing to complex diseases

Targeted sequencing to identify novel genetic risk factors for deep vein thrombosis: a study of 734 genes

Essentials Deep vein thrombosis (DVT) has a large unknown genetic component. We sequenced coding areas of 734 hemostasis-related genes in 899 DVT patients and 599 controls. Variants in F5, FGA-FGG, CYP4V2-KLKB1-F11, and ABO were associated with DVT risk. Associations in KLKB1 and F5 suggest a more complex genetic architecture than previously thought. Summary: Background Although several genetic risk factors for deep vein thrombosis (DVT) are known, almost all related to hemostasis, a large genetic component remains unexplained. Objectives To identify novel genetic determinants by using targeted DNA sequencing. Patients/Methods We included 899 DVT patients and 599 controls from three case\u2013control studies (DVT-Milan, Multiple Environmental and Genetic Assessment of risk factors for venous thrombosis [MEGA], and the Thrombophilia, Hypercoagulability and Environmental Risks in Venous Thromboembolism [THE-VTE] study) for sequencing of the coding regions of 734 genes involved in hemostasis or related pathways. We performed single-variant association tests for common variants (minor allele frequency [MAF] 65 1%) and gene-based tests for rare variants (MAF 64 1%), accounting for multiple testing by use of the false discovery rate (FDR). Results Sixty-two of 3617 common variants were associated with DVT risk (FDR 0.2). Conclusions We confirmed associations between DVT and common variants in F5,ABO,FGA\u2013FGG, and CYP4V2\u2013KLKB1\u2013F11, and observed secondary signals in F5 and CYP4V2\u2013KLKB1\u2013F11 that warrant replication and fine-mapping in larger studies

Genome-wide association and Mendelian randomisation analysis provide insights into the pathogenesis of heart failure

Heart failure (HF) is a leading cause of morbidity and mortality worldwide. A small proportion of HF cases are attributable to monogenic cardiomyopathies and existing genome-wide association studies (GWAS) have yielded only limited insights, leaving the observed heritability of HF largely unexplained. We report results from a GWAS meta-analysis of HF comprising 47,309 cases and 930,014 controls. Twelve independent variants at 11 genomic loci are associated with HF, all of which demonstrate one or more associations with coronary artery disease (CAD), atrial fibrillation, or reduced left ventricular function, suggesting shared genetic aetiology. Functional analysis of non-CAD-associated loci implicate genes involved in cardiac development (MYOZ1, SYNPO2L), protein homoeostasis (BAG3), and cellular senescence (CDKN1A). Mendelian randomisation analysis supports causal roles for several HF risk factors, and demonstrates CAD-independent effects for atrial fibrillation, body mass index, and hypertension. These findings extend our knowledge of the pathways underlying HF and may inform new therapeutic strategies

STUDIES ON THE GENETIC PREDISPOSITION TO COMMON THROMBOTIC DISEASES

Common thrombotic diseases (i.e. myocardial infarction, MI; ischemic stroke; deep vein thrombosis, DVT) are the main cause of death and disability worldwide. These diseases are highly heritable. From a genetic standpoint common thrombotic diseases are classified as complex, because their inheritance is believed to arise from several different genetic variants, interacting among themselves and with environmental exposures. Genome-wide association studies (GWAS) have represented a major step forward in deciphering the genetics of such complex traits as cardiovascular diseases, having identified several hundred SNPs associated with common diseases. In spite of these recent advances, however, genetic variants established to influence the risk for common thrombotic diseases explain only a fraction of disease heritability. Using early-onset disease as a model, we studied the predisposition to common thrombotic diseases using different approaches for genetic and association analysis. We also conducted an exploratory study using cutting-edge next-generation sequencing technology for the identification of causal genes/variants in DVT. We confirmed associations of candidate variants with predisposition to common cardiovascular diseases and we identified several novel variants potentially associated with the development of these common, life-threatening diseases

Pathophysiology of thrombotic thrombocytopenic purpura : the "two-hit" paradigm

Thrombotic thrombocytopenic purpura (TTP) is a rare, life-threatening disease characterized by acute episodes of widespread thrombosis in capillaries and small arteries. The discovery that the plasmatic activity of the von Willebrand factor cleaving protease, ADAMTS13, is severely deficient in patients with TTP represented a turning point in the understanding of the pathophysiology of the disease. In spite of recent advances, the clinical course of TTP is characterized by considerable heterogeneity, the causes of which are largely unknown. Herein, we present a number of studies investigating the determinants of clinical heterogeneity in patients with both congenital and acquired forms of TTP. A __two-hit__ model of the pathophysiology of TTP is presented