Biomedical subjects

S Akhavan

Publications and source records attributed to S Akhavan.

8 recordsLinked to original sources

PubMed2005

A critical role for Gly25 in the B chain of human thrombin.

We have recently identified (Akhavan S et al., Thromb Haemost 2000; 84: 989-97) a patient with a mild bleeding diathesis associated to an homozygous mutation in the thrombin B chain (Gly25Ser, chymotrypsinogen numbering, i.e. position 330 in human prothrombin numbering). Transient transfection of wild-type prothrombin (FII-WT) and mutant prothrombin (designated FII-G25(330)S) cDNA in COS-7 cells showed a mild reduction (50%) in FII-G25(330)S production. Recombinant proteins, stably expressed in Chinese hamster ovary cells, were isolated and activated by Taipan snake or Echis carinatus venoms. We show that the G25(330)S mutation results in a decrease in the rate of prothrombin proteolytic activation. The mutation also significantly decreases (i) the catalytic activity of thrombin with a 9-fold reduction in catalytic efficiency of the mutant toward S-2238; (ii) the interaction with benzamidine; (iii) the rate of inhibition by TLCK and antithrombin; and (iv) the rate of hydrolysis of macromolecular substrates (fibrinogen, protein C). In contrast, exosite I does not appear to be affected by the molecular defect. These results, together with molecular modeling and dynamics, indicate that Gly25(330) is important for proper expression and probably proper folding of prothrombin, and also plays a critical role in both the alignment of the catalytic triad and the flexibility of one of the activation segments of prothrombin.

Animals↗

PubMed2002

Rare coagulation deficiencies.

UNLABELLED: Deficiencies of coagulation factors (other than factor VIII and factor IX) that cause a bleeding disorder are inherited as autosomal recessive traits and are generally rare, with prevalences in the general population varying between 1 : 500 000 and 1 : 2 000 000. In the last few years, the number of patients with recessively transmitted coagulation deficiencies has increased in European countries with a high rate of immigration of Islamic populations, because in these populations, consanguineous marriages are frequent. Owing to the relative rarity of these deficiencies, the type and severity of bleeding symptoms, the underlying molecular defects and the actual management of bleeding episodes are not as well established as for haemophilia A and B. This article reviews these disorders in terms of their clinical manifestations and characterization of the molecular defects involved. The general principles of management are also discussed. KEYWORDS: afibrinogenaemia, autosomal recessive disorders, factor VIII, factor XI, factor XIII.

Blood Coagulation Factors↗

PubMed2000

A novel polymorphism in intron 1a of the human factor VII gene (G73A): study of a healthy Italian population and of 190 young survivors of myocardial infarction.

We have identified a novel polymorphism located in intron 1a of the human factor VII gene, caused by the nucleotide change G to A at position + 73. In a population of 128 healthy individuals from northern Italy, the variant A73 allele had a frequency of 0.21, whereas the frequency of the previously reported 10 bp insertion allele located at -323 in the promoter region was 0.17 and that of the Q353 allele in the catalytic region of the factor VII gene was 0. 20. In 75% of the healthy individuals, the A73 allele was present together with the 10 bp insertion and the Q353 alleles, indicating a strong linkage disequilibrium. The concomitant presence of A73 with both the 10 bp and the Q353 alleles was associated with the lowest factor VII levels, measured as coagulant activity, activated factor VII and factor VII antigen. The G73A polymorphism was also evaluated in 190 survivors of myocardial infarction who had experienced the event before the age of 45 years and in 179 individuals with a negative exercise test matched with patients for sex, age and geographical origin. Patients carrying the A73 allele associated with lower factor VII levels tended to have a lower risk of myocardial infarction (adjusted odds ratio 0.54; 95% confidence intervals 0.29-0.99). In conclusion, we found a novel variant allele in intron 1a of the human factor VII gene that is often associated in healthy individuals with the 10 bp and Q353 alleles in the promoter and catalytic region of the same gene. This intronic mutation, alone or in association with other factor VII gene polymorphisms, might confer protection against myocardial infarction in the young.

Adolescent↗

PubMed2000

Identification and three-dimensional structural analysis of nine novel mutations in patients with prothrombin deficiency.

Prothrombin deficiency is an autosomal recessive disorder associated with a moderately severe bleeding tendency. In this study, 13 patients with prothrombin deficiency were screened for the presence of alterations in the prothrombin gene, and nine novel candidate mutations were identified. Of 11 patients with hypoprothrombinemia, ten are homozygous for five mutations and one patient is a compound heterozygote. The two patients with dysprothrombinemia are homozygous for two mutations. Eight of nine mutations are missense ones associated with single amino acid substitutions in the propeptide (Arg-1Gln, Arg-2Trp), the kringle-1 (Asp118Try) and kringle-2 (Arg220Cys) domains and the catalytic serine protease domain (Gly330Ser, Ser354Arg. Arg382His and Arg538Cys). The ninth mutation is an in-frame deletion of 3 bp that results in the omission of one amino acid (del Lys 301/302). The combination of these missense mutations with crystal structures for alpha-thrombin and the prothrombin fragments 1 and 2 resulted in new insight into the function of alpha-thrombin. The hypoprothrombinemia mutations were inferred to affect either the cleavage of the propeptide from the Gla domain, the stability of the kringle-1 and -2 domains, or the close association of the A and B chains of the serine protease domain. The dysprothrombinemia mutations were inferred to directly affect catalytic function through their location at the active site crevice or exosite 1 within the serine protease domain.

Adolescent↗

PubMed1999

Gly319 --> arg substitution in the dysfunctional prothrombin Segovia.

The molecular defect of a congenitally dysfunctional form of prothrombin, prothrombin Segovia, was identified in a patient with a severe bleeding tendency, reduced prothrombin coagulant activity, and normal antigen level. Nucleotide sequencing of amplified DNA revealed a G --> A change at nucleotide 7539 of exon 9 of the prothrombin gene. This resulted in the substitution of Gly319 by Arg. The proband was homozygous for this mutation, his father and brother were heterozygous. We surmised that the substitution, which occurs near the site of cleavage of prothrombin by factor Xa (Arg320-Ile321), altered the conformation of the protein making the cleavage site inaccessible.

Adult↗

PubMed1999

Interaction between the G20210A mutation of the prothrombin gene and oral contraceptive use in deep vein thrombosis.

Single-point mutations in the gene coding for prothrombin (factor II:A20210) or factor V (factor V:A1691) are associated with an increased risk of venous thromboembolism. The use of oral contraceptives is also a strong and independent risk factor for the disease, and the interaction between factor V:A1691 and oral contraceptives greatly increases the risk. No information is available about the interaction between oral contraceptives and mutant prothrombin. We investigated 148 women with a first, objectively confirmed episode of deep vein thrombosis and 277 healthy women as controls. Fourteen patients (9.4%) were carriers of factor II:A20210, 24 (16.2%) of factor V:A1691, and 4 (2.7%) of both defects. Among controls, the prevalence was 2.5% for either factor II:A20210 or factor V:A1691, and there was no carrier of both the mutations. The relative risk of thrombosis was 6-fold for factor II:A20210 and 9-fold for factor V:A1691. The most prevalent circumstantial risk factor in patients and the only one observed in controls was oral contraceptive use, which per se conferred a 6-fold increased risk of thrombosis. The risk increased to 16.3 and 20.0 when women with factor II:A20210 or factor V:A1691 who used oral contraceptives were compared with noncarriers and nonusers. These figures indicate a multiplicative interaction between the genetic risk factors and oral contraceptives. No difference in the type of oral contraceptives was observed between patients and controls, those of third generation being the most frequently used (73% and 80%). We conclude that carriers of the prothrombin mutation who use oral contraceptives have a markedly increased risk of deep vein thrombosis, much higher than the risk conferred by either factor alone.

Adolescent↗

PubMed1998

Suicidality and cognitive vulnerability to depression among college students: a prospective study.

Using a behavioral high-risk two-site prospective design, we tested the cognitive vulnerability hypotheses about suicidality. Consistent with prediction, the high cognitive risk (HR) participants were more likely than the low cognitive risk (LR) participants to exhibit suicidality, measured by both structured diagnostic interview and questionnaire self-report, during the 2 1/2 year prospective follow-up period. Moreover, when the prospective period was examined as a whole, the mediation hypothesis derived from the cognitive theories was strongly supported. Hopelessness appeared to mediate the obtained relationship between cognitive vulnerability and suicidality. Finally, the obtained relationship between cognitive vulnerability and suicidality was not mediated by other hypothesized risk factors for suicidality not specified in the cognitive theories, such as past suicidality, personal history of depressive disorders, borderline and antisocial personality dysfunction, and parental history of depression.

Adolescent↗

PubMed1998

Laboratory screening of thrombophilia. Evaluation of the diagnostic efficacy of a global test to detect congenital deficiencies of the protein C anticoagulant pathway.

Clinical laboratories are at present confronted with increasing demands for thrombophilia work-up, which may seriously overwhelm their capacity. Recently, methods able to investigate the protein C anticoagulant pathway globally have been proposed. In this study we investigated the reliability of one such method for its ability to detect patients with known defects of the pathway by testing plasmas from patients with the FVQ506 mutation, with congenital protein C, protein S or antithrombin deficiencies, and patients with previous history of thrombosis, but no identifiable defects. The results show that the new global test fulfils the requirements for congenital protein C deficiency and activated protein C resistance associated with the FVQ506 mutation, which account for more than half of the congenital defects found in thrombophilia. However, congenital protein S deficiency very often remains undetected by this test. Improvement of sensitivity toward this component of the protein C anticoagulant pathway would enroll the global test as a suitable candidate to explore the pathway. Since antithrombin, which also remains undetected by this test, is an additional important risk factor for venous thrombosis, devoting time and effort to developing global tests able to detect defects in both the antithrombin and protein C pathways is warranted.

Activated Protein C Resistance↗