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Biomedical subjects

P Simioni

Publications and source records attributed to P Simioni.

At least 19 recordsLinked to original sources
PubMed2005

Megakaryocytes endocytose and subsequently modify human factor V in vivo to form the entire pool of a unique platelet-derived cofactor.

Factor Va (FVa), derived from plasma or released from stimulated platelets, is the essential cofactor in thrombin production catalyzed by the prothrombinase complex. Plasma-derived factor V (FV) is synthesized in the liver. The source(s) of the platelet-derived cofactor remains in question. We identified a patient homozygous for the FV(Leiden) mutation, who received a liver transplant from a homozygous wild-type FV donor. Eighteen days post-transplant, phenotypic analysis of the patient's platelet-derived FV indicated that the platelets were acquiring wild-type FV, consistent with the temporal differentiation of megakaryocytes and subsequent platelet production. Nine months post-transplant, the platelet-derived FV pool consisted entirely of wild-type FV. Consequently, megakaryocyte endocytosis of plasma-derived FV must account for the entire platelet-derived pool, because blood-borne platelets cannot bind or endocytose FV. Subsequent to this endocytic process, the patient's platelet-derived FV was cleaved to a partially active cofactor, and rendered resistant to phosphorylation catalyzed by a platelet-associated kinase, and hence less susceptible to activated protein C-catalyzed inactivation. These data provide the first in vivo demonstration of an endocytosed plasma protein undergoing intracellular modifications that alter its function. This process results in the sequestration of active FVa within the platelet compartment, poised for immediate action subsequent to release from platelets at a site of injury.

Adult↗
PubMed2005

The incidence of venous thromboembolism in carriers of antithrombin, protein C or protein S deficiency associated with the HR2 haplotype of factor V: a family cohort study.

In order to assess whether the HR2 haplotype of the factor V gene (HR2) increases the risk of venous thromboembolism (VTE) in carriers of antithrombin (AT), protein C (PC) or S (PS) defects, we performed this determination in 336 subjects, who were family members of 66 symptomatic patients with clotting inhibitors defects. We first assessed the presence of previous VTE, and then followed prospectively subjects without prior VTE. VTE episodes had occurred in 26 individuals: 18 in 139 carriers of clotting inhibitors defects alone (annual incidence, 0.55%), four in 33 carriers of clotting inhibitors defects combined with HR2 (0.52%) and four in 151 non-carriers (0.1%), resulting in a relative risk (RR) for VTE of 4.9 (95% CI: 1.7-14.4) and 4.62 (95% CI: 1.2-18.4), respectively. After an overall follow-up of 2557 patient-years, VTE episodes developed in 12 subjects: nine in 121 carriers of clotting inhibitors defects alone (annual incidence, 0.92%), three in 29 carriers of clotting inhibitors defects combined with HR2 (1.0%) and none in 147 non-carriers. In family members of patients with AT, PC or PS defects the coinheritance of HR2 haplotype does not seem to increase the thromboembolic risk.

Adult↗
PubMed2005

Expression of the normal factor V allele modulates the APC resistance phenotype in heterozygous carriers of the factor V Leiden mutation.

BACKGROUND: Functional defects of the protein C pathway, detectable in plasma as activated protein C (APC) resistance, are a prevalent risk factor for venous thrombosis. The factor V (FV) Leiden mutation causes APC resistance by interfering with the APC-mediated inactivation of both FVa and FVIIIa. Co-inheritance of FV Leiden and quantitative FV deficiency on different alleles, a rare condition known as pseudo-homozygous APC resistance, is associated with pronounced APC resistance and 50% reduced FV levels, because of non-expression of the non-Leiden FV allele. OBJECTIVES: The role of normal FV in modulating the APC resistance phenotype in carriers of FV Leiden was investigated in patients with pseudo-homozygous APC resistance and in model systems. PATIENTS/METHODS: Four functional plasma assays probing both components of APC resistance (susceptibility of FVa to APC and cofactor activity of FV in FVIIIa inactivation) were employed to compare seven clinically and genetically characterized FV Leiden pseudo-homozygotes to 30 relatives with different FV genotypes (including 12 FV Leiden heterozygotes and seven carriers of FV deficiency) and to 32 unrelated FV Leiden homozygotes. RESULTS AND CONCLUSIONS: All assays consistently indicated that FV Leiden pseudo-homozygotes are significantly more APC-resistant than heterozygotes and indistinguishable from homozygotes. Thrombin generation measurements in FV-deficient plasma reconstituted with purified normal FV and FV Leiden confirmed these observations and showed that the expression of the normal FV allele is an important modulator of APC resistance in FV Leiden heterozygotes. These findings provide an explanation for the higher thrombotic risk of FV Leiden pseudo-homozygotes when compared with heterozygotes.

Activated Protein C Resistance↗
PubMed2003

[Therapeutic indications for acute venous thromboembolism. Current status and future perspectives].

Except for selected patients requiring aggressive therapies, the large majority of patients with acute venous thromboembolism are currently treated with full doses of unfractionated or low-molecular-weight heparins (LMWH) followed by oral anticoagulants for variable periods of time. LMWHs present a number of potential advantages over unfractionated heparin: a longer plasma half-life, improved subcutaneous bioavailability, and a more predictable dose-response relationship. As a result of these pharmacokinetic properties, these compounds have the potential to greatly simplify the initial treatment of venous thromboembolism, making the treatment of suitable patients feasible in an outpatient setting with considerable saving in costs and improvement in patients' quality of life. The use of unfractionated heparin is still desirable in the initial treatment of acute pulmonary embolism in non-critically ill patients. The use of heparin protocols assures that virtually all patients will promptly achieve the therapeutic range for the activated partial thromboplastin time. Although the optimal duration of anticoagulation in patients suffering an episode of venous thromboembolism is presently unknown, it seems reasonable to administer a short-term course of coumarin drugs to patients with thrombosis associated with transient risk factors, while a longer course should be considered in patients with idiopathic thrombosis and in those with permanent risk factors. At present, indefinite anticoagulant therapy remains a clinical judgment in the individual patient. The efficacy and safety of emerging drugs (pentasaccharide, ximelagatran) in the treatment and secondary prevention of venous thromboembolic disorders is currently under investigation.

Acute Disease↗
PubMed2002

A matrix-assisted laser desorption/ionization time-of-flight based method for screening the 1691G --> A mutation in the factor V gene.

A point mutation, 1691 G --> A in the coagulation factor V gene results in an Arg506 --> Gln amino acid substitution in the factor V molecule. This mutation, defined as factor VLEIDEN, results in activated protein C (APC) resistance and is the most common genetic risk factor for familial thrombophilia. A new mini-sequencing method using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry was developed for the screening of the 1691G --> A substitution in factor V. In this method, a fragment of genomic DNA containing the 1691st base is first amplified, followed by mini-sequencing in the presence of dGTP and ddATP, ddCTP, and ddTTP. In this manner, the primer is extended by one base from one allele and two bases from the other allele. The extended products are analyzed using MALDI-TOF mass spectrometry. The base at position 1691 is identified based on the number of nucleotides added. We have used this method to genotype 16 APC-resistant patients previously identified by conventional methods and 11 normal control samples. The genotypes of all samples were correctly identified. This method is accurate, fast, and potentially allows for simultaneous multiplex genotyping of a number of mutation sites associated with thrombophilia and clot formation.

Activated Protein C Resistance↗
PubMed2002

Activated protein C resistance in normal and pre-eclamptic pregnancies.

OBJECTIVES: A lower ratio in the classic activated protein C resistance (APC-R) test has been reported during pregnancy, which has been called 'acquired' APC-R. However, little is known about the cause of the lowered ratio, and whether or not there is a correlation with blood coagulation activation. The primary objective of our study was to determine changes in APC-R levels in each of the trimesters of normal pregnancy. The secondary objective was to confirm whether APC-R levels were lower in pregnancies complicated by pre-eclampsia than in a control group. Finally, this prospective study was performed to investigate the prevalence of APC-R among pregnant women and to elucidate its obstetric consequences. METHODS: We enrolled 35 healthy pregnant women and 47 pregnant women affected by pre-eclampsia in our study. The following laboratory tests were performed: prothrombin time, partial thromboplastin time, fibrinogen levels, antithrombin III, plasmatic fibronectin (as a marker of endothelial damage), haptoglobin (as a marker of intravascular haemolysis), a functional test for APC-R and analysis of factor V Leiden mutation by polymerase chain reaction. RESULTS: The activated protein C sensitivity ratio was lower in the pathological group than in the control group (p = 0.008 and p = 0.02, respectively). Plasmatic fibronectin was found to be higher in the pathological group than in the control group (p = 0.05). Finally, the overall prevalence of factor V Leiden mutation was 5.4%, i.e. 2/35 women (5.7%) in the control group and 3/47 women in the pathological group (6.38%). CONCLUSIONS: The APC ratio decreased after 20 weeks of gestation until week 42. This decrease was most pronounced in the third trimester, in which resistance was demonstrated in 34.2% of control group patients. In pre-eclampsia, we found a greater reduction of the APC ratio than in controls. We hypothesise that this is due to a decrease in the plasmatic levels of coagulation inhibitors and an increase in coagulatory factors.

Activated Protein C Resistance↗
PubMed2002

Seasonal variation in the incidence of deep vein thrombosis in patients with deficiency of protein C or protein S.

An attempt was made to identify circaseptanal or seasonal variation of deep vein thrombosis (DVT) in a population with protein C or protein S deficit. Forty-four patients with DVT and protein C or protein S deficit were studied for 1 year. A significant circannual rhythm was found for the total population that peaked during winter. There was also a significant falling circaseptanal rhythm on Fridays. These observations may optimize an adequate and precise anticoagulant therapy in patients with protein C or protein S deficits.

Adult↗
PubMed2001

Long-term use of oral contraceptive therapy in women with the prothrombin 20210 G-A polymorphism without thrombotic complications: a study of 13 women (12 heterozygotes and 1 homozygote).

Thirteen female patients with the prothrombin 20210 G-A abnormality (twelve heterozygotes and one homozygote) were selected out of 551 patients admitted to our Department of Medicine or to our Outpatient Hemostasis Units between January 1999 and October 2000. The selection was based on the fact that all patients had taken or were still taking oral contraceptives (OC) for a period of 3 years or longer than 3 years. None of these patents as gathered from history, physical examination, private physician records and our records has shown any DVT during or immediately after OC intake. Physical and compression ultrasonography examinations at the time of study were all negative. The average length of oral contraceptives therapy (OCT) was 10 years (range 3-23). The average age of patients at the time of oral contraception was 30 years. The 13 women had also 17 pregnancies without any venous thrombosis. The observations casts several doubt about the prothrombotic effect of this polymorphism. Since DVT has been shown to occur occasionally even in normal women, it is likely that the same may occur in women with this polymorphism regardless of the existence or not of any pathogenetic relationship between the two phenomena. Occasional reports suggesting a link between this polymorphism and oral contraception-related venous thrombosis should be carefully evaluated in order to avoid premature and incorrect conclusions.

Adult↗
PubMed2001

A dysfunctional factor X (factor X San Giovanni Rotondo) present at homozygous and double heterozygous level: identification of a novel microdeletion (delC556) and missense mutation (Lys(408)-->Asn) in the factor X gene. A study of an Italian family.

Low levels of factor X (F.X) were detected in a 4-year-old boy who experienced acute lymphoblastic leukemia and bleeding manifestations. Laboratory data suggested the presence of a dysfunctional F.X molecule. Two novel F.X gene mutations were identified in the proband that was double heterozygous for both: a microdeletion (delC556) in exon VI resulting in a frameshift leading to a termination codon at position 226. This deletion was found in six family members with reduced F.X antigen and activity levels. A second mutation characterised by a G(1344)-->C transversion in exon VIII was detected in the proband resulting in a Lys(408)-->Asn substitution. This latter mutation was present in several asymptomatic family members from the paternal and the maternal side. The proband's sister was homozygous for the Lys(408)-->Asn substitution and exhibited low F.X activity with a normal antigen level. The naturally occurring F.X Lys(408)-->Asn (F.X(K408N)) variant was isolated from plasma of either homozygous or double heterozygous individuals. NH(2)-terminal sequencing of the heavy chain of F.X(K408N) failed to show any sequence abnormality in patients who were also carriers of the delC556, suggesting that this latter lesion accounted for the lack of F.X synthesis. Purified F.X Lys(408)-->Asn had an identical behaviour to normal F.X as judged by SDS-PAGE and immunoblotting. Clotting assay using purified F.X(K408N) and F.X-deficient plasma resulted in a laboratory phenotype similar to that observed in a homozygous subject for F.X Lys(408)-->Asn substitution. This is the first characterisation of a naturally occurring F.X variant with a mutation at the COOH-terminal end of the molecule.

Amino Acid Sequence↗
PubMed2001

Factor V Leiden and prothrombin gene mutation in inflammatory bowel disease in a Mediterranean area.

BACKGROUND: Thromboembolism has been reported to be associated with inflammatory bowel disease. AIM: To evaluate the association of factor V Leiden and prothrombin gene mutation with inflammatory bowel disease in a population of patients with thromboembolic events and inflammatory bowel disease and in a control population of patients with inflammatory bowel disease without thromboembolic events. PATIENTS AND METHODS: A series of 18 patients with inflammatory bowel disease and a history of arterial or venous thrombosis and 45 patients with inflammatory bowel disease without thromboembolic events were evaluated for the presence of factor V Leiden and prothrombin gene mutation. Frequency of gene mutation was compared with its occurrence in 100 healthy controls. RESULTS: One patient with inflammatory bowel disease without thromboembolic events was heterozygous for factor V Leiden mutation. whereas no patient with a thromboembolic event had factor V Leiden mutation. No patients (either cases or controls) had prothrombin gene mutation. In the healthy population the frequency of factor V Leiden and prothrombin mutation was 5% and 2%, respectively. CONCLUSIONS: Data emerging from the present study do not support any role of factor V Leiden and prothrombin gene mutation as the cause of thromboembolism in inflammatory bowel disease.

Colitis, Ulcerative↗
PubMed2001

A highly polymorphic microsatellite in the factor V gene is an informative tool for the study of factor V-related disorders.

The role of factor V (FV) mutations in activated protein C (APC) resistance and FV deficiency is well established. We report on the identification of a highly polymorphic (AT)n microsatellite marker in the FV gene, which represents an informative tool for the investigation of the origin and evolution of pathologically relevant FV genetic components. A high number of different microsatellite alleles were found to be associated with FV R506Q and FV H1299R, two single-origin mutations. An example of the use of the microsatellite marker in family studies of thrombophilia and FV deficiency is also provided.

Factor V↗
PubMed2001

Postthrombotic syndrome: incidence, prevention, and management.

Mild to severe postthrombotic sequelae, including chronic pain, edema, and ulceration, arise in one third of patients short after deep vein thrombosis (DVT). Recurrent DVT is closely associated with the development of postthrombotic syndrome (PTS), whereas if the extent and location of DVT might be relevant remains unclear. Chronic venous hypertension and abnormal microvessel or lymphatic function also correlates with PTS. The diagnosis of PTS is based on clinical grounds only if patients report a history of documented DVT; otherwise, objective testing is required. To abate the prevalence of PTS, the best policy is represented by prevention of recurrent thrombosis and use of stockings. Despite a plenty of surgical options, conservative treatment is preferable because half of the patients improve or remain stable during follow-up, provided they wear elastic stockings. Clinical presentation has a prognostic value, as patients with initially severe symptoms enjoy a more favorable outcome than those who progressively deteriorate over time.

Anticoagulants↗
PubMed2001

ProC global: a new automated screening assay for the evaluation of total function of the protein C system.

Protein C (PC) pathway represents a major physiologic inhibitory mechanism regulating the coagulation cascade. A new automated functional screening assay (ProC Global) for the evaluation of the PC-system was tested to define its ability to identify patients with known inherited defects such as factor V (FV) Leiden mutation and PC and protein S (PS) deficiency. A total of 249 patients who were symptomatic or asymptomatic for previous venous thromboembolism (VTE) were evaluated, 50 of whom had FV Leiden mutation, 36 had PC deficiency, and 34 had PS deficiency. One hundred healthy subjects were also tested, as well as 40 blood donors of both sexes in whom coagulation abnormalities were not found. Results of ProC Global test were expressed as normalized ratio (NR) and values below an established cut-off level were consistent with a positive test. ProC Global was positive in all 50 patients with the FV Leiden mutation (mean NR = 0.59; range, 0.37 to 0.69). ProC Global correctly identified 32 of 36 (89%) PC defects (mean NR = 0.63; range, 0.34 to 1.21) and 25 of 34 (73.5%) PS defects (mean NR = 0.76; range, 0.5 to 1.23). Overall, 92.5% of hereditary defects of the PC system considered in this study were identified by ProC Global test. ProC Global exhibited NR above cut-off level in all 40 blood donors without coagulation defects. ProC Global is a new automated screening test with some diagnostic potential in identifying patients with defects of the PC system. However, ProC Global in its current form cannot substitute the assay of each single component of this inhibitory system in the daily screening for thrombophilia.

Adolescent↗