Dimeric FcγR ectodomains detect pathogenic anti-platelet factor 4-heparin antibodies in heparin-induced thromobocytopenia

Essentials FcγRIIa mediates life-threatening heparin-induced thrombocytopenia (HIT). Most anti-platelet factor (PF)4-heparin IgGs are not pathogenic so diagnosis of HIT is challenging. Dimeric rsFcγRIIa was used to quantify receptor-binding activity of anti-PF4-heparin antibodies. Dimeric rsFcγRIIa binding specifically correlated with occurrence of HIT. SUMMARY: Background Heparin-induced thrombocytopenia (HIT) is a major and potentially fatal consequence of antibodies produced against platelet factor 4 (PF4)-heparin complexes following heparin exposure. Not all anti-PF4-heparin antibodies are pathogenic, so overdiagnosis can occur, with resulting inappropriate use of alternative anticoagulation therapies that have associated risks of bleeding. However, definitive platelet functional assays are not widely available for routine analysis. Objectives To assess the utility of dimeric recombinant soluble FcγRIIa (rsFcγRIIa) ectodomains for detecting HIT antibodies. Patients/Methods Plasma from 27 suspected HIT patients were tested for pathogenic anti-PF4-heparin antibodies by binding of a novel dimeric FcγRIIa ectodomain probe. Plasmas were also tested by the use of PF4-heparin IgG ELISA, the HemosIL AcuStar HIT IgG-specific assay, and a serotonin release assay (SRA). Results The dimeric rsFcγRIIa test produced no false positives and excluded four samples that were positive by IgG ELISA. In this small patient cohort, the novel assay correctly assigned 93% of the suspected HIT patients, with two of the HIT patients being scored as false negatives. The improved discrimination of the novel assay over the IgG ELISA, which scored four false positives, supports the mechanistic interpretation that binding of dimeric rsFcγRIIa detects pairs of closely spaced IgG antibodies in PF4-heparin immune complexes. Conclusions This study found the cell-free, function-based dimeric rsFcγRIIa assay to be convenient, simple, and potentially predictive of HIT. The assay had improved specificity over the IgG ELISA, and correlated strongly with the AcuStar HIT IgG-specific assay, warranting further evaluation of its potential to identify HIT in larger patient cohorts.

No Association between the 20210 G/A Prothrombin Gene Mutation and Premature Coronary Artery Disease

The 20210 G/A prothrombin gene mutation is associated with an increased risk of venous thrombosis but whether there is an association of the mutation with premature coronary artery disease and acute myocardial infarction remains unclear.

To further assess the role of the G/A genotype as a risk factor for arterial vascular disease, we performed a case-control study of 644 patients aged less than 50 years with angiographically proven coronary artery disease, 402 of whom had myocardial infarction, and 679 unrelated healthy control subjects aged less than 50 years, randomly selected from the electoral roll.

The prevalence of the G/A genotype was 2.5% in patients with coronary artery disease, and 3.2% in control subjects (odds ratio 0.8; 95% confidence interval 0.35 to 1.83). The mutation was not more frequent among patients with a history of myocardial infarction (2.2%, odds ratio 0.7; 95% confidence interval 0.27 to 2.05), and there was no evidence of an interaction between the prothrombin mutation and conventional cardiovascular disease risk factors. There was no association between genotype and extent of angiographic coronary artery disease (p = 0.73).

We conclude that the 20210 G/A prothrombin gene mutation is not a major risk factor for premature coronary artery disease in our predominantly Caucasian Australian population.

Identification of reference miRNAs in plasma useful for the study of oestrogen-responsive miRNAs associated with acquired Protein S deficiency in pregnancy

Background

Accumulating evidence indicate that circulating microRNAs (miRNAs) are useful independent non-invasive biomarkers, with unique miRNA signatures defined for various pathophysiological conditions. However, there are no established universal housekeeping miRNAs for the normalisation of miRNAs in body fluids. We have previously identified an oestrogen-responsive miRNA, miR-494, in regulating the anticoagulant, Protein S, in HuH-7 liver cells. Moreover, increased thrombotic risk associated with elevated circulating oestrogen levels is frequently observed in pregnant women and oral contraceptive users. In order to identify other oestrogen-responsive miRNAs, including miR-494, that may be indicative of increased thrombotic risk in plasma, we used nanoString analysis to identify robust and stable endogenous reference miRNAs for the study of oestrogen-responsive miRNAs in plasma.

Results

We compared the plasma miRNA expression profile of individuals with: (1) Low circulating oestrogens (healthy men and non-pregnant women not taking oral contraceptives), (2) High circulating synthetic oestrogens, (women taking oral contraceptives) and (3) High circulating natural oestrogens (pregnant females >14 weeks gestation). From the nanoString analyses, 11 candidate reference miRNAs which exhibited high counts and not significantly differentially expressed between groups were selected for validation using realtime quantitative polymerase chain reaction (RT-qPCR) and digital droplet PCR (DDPCR) in pooled plasma samples, and the stability of their expression evaluated using NormFinder and BestKeeper algorithms. Four miRNAs (miR-25-5p, miR-188-5p, miR-222-3p and miR-520f) demonstrated detectable stable expression between groups and were further analysed by RT-qPCR in individual plasma samples, where miR-188-5p and miR-222-3p expression were identified as a stable pair of reference genes. The miRNA reference panel consisting of synthetic spike-ins cel-miR-39 and ath-miR159a, and reference miRNAs, miR-188-5p and miR-222-3p was useful in evaluating fold-change of the pregnancy-associated miRNA, miR-141-3p, between groups.

Conclusion

The miRNA reference panel will be useful for normalising qPCR data comparing miRNA expression between men and women, non-pregnant and pregnant females, and the potential effects of endogenous and synthetic oestrogens on plasma miRNA expression.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-017-2636-3) contains supplementary material, which is available to authorized users.

Micro-ribonucleic Acid 494 regulation of protein S expression

BACKGROUND

Acquired protein S (PS) deficiency is highly associated with elevated circulating estrogen levels resulting from pregnancy, oral contraceptives, and estrogen replacement therapy; however, the mechanism of estrogen-mediated acquired PS deficiency remains poorly understood. Increasing evidence indicates that estrogen receptor signaling can indirectly modulate the expression of target genes at the post-transcriptional level by modulating the expression of microRNAs (miRNAs), and miRNAs have also been demonstrated to be involved in the regulation of hemostasis.

OBJECTIVES

To investigate the mechanism of estrogen-mediated downregulation of PROS1 expression by the microRNA miR-494.

METHODS

Computational analyses of the PROS1 3'-untranslated region (UTR) were performed to identify putative miRNA-binding sites, and direct targeting of the PROS1 3'-UTR by miR-494 was determined with dual luciferase reporter assays in HuH-7 cells. Reporter vectors containing the PROS1 3'-UTR sequence with deleted miR-494-binding sites were also analyzed with luciferase reporter assays. The effects of estrogen on miR-494 and PROS1 mRNA levels in HuH-7 cells were determined by quantitative real-time PCR, and estrogen-mediated changes to secreted PS levels in culture supernatant of HuH-7 cells were measured with an ELISA.

RESULTS

The PROS1 3'-UTR sequence contains three putative miR-494-binding sites. miR-494 directly targets PROS1, and miR-494 levels are upregulated following estrogen treatment in HuH-7 liver cells in association with downregulated PROS1 mRNA and PS levels.

CONCLUSIONS

The results from this study provide the first evidence for miRNA downregulation of PROS1 by miR-494, and suggest that miR-494 is involved in the mechanism of estrogen-mediated downregulation of PS expression.

Clinical efficacy and safety of the factor VIII/von Willebrand factor concentrate BIOSTATE in patients with von Willebrand's disease: a prospective multi-centre study

von Willebrand's disease (VWD) is an inherited bleeding disorder characterized by deficient levels of or dysfunctional von Willebrand factor (VWF). This phase II/III open-label, multicentre study evaluated the efficacy and safety of BIOSTATE, a high purity plasma-derived double-virus inactivated FVIII/VWF concentrate, when used in non-surgical bleeds, surgical procedures and prophylactic therapy in VWD patients for whom desmopressin treatment was deemed ineffective, inadequate or contraindicated. Twenty three patients (7 type 1, 9 type 2 and 7 type 3; 12 male, 11 female), who received FVIII/VWF concentrate as part of their VWD management, were recruited prospectively between December 2004 and May 2007 from eight centres in Australia and New Zealand. BIOSTATE dosing was based on pre-treatment FVIII:C and/or VWF:RCo plasma levels and a predetermined dosing guide. Haemostatic efficacy of BIOSTATE was rated as excellent or good for all major and minor surgery events, long-term prophylaxis, and for four of the six assessable non-surgical bleeding events. Blood transfusions were required by two major surgery patients as well as one patient with a non-surgical bleed. The median overall exposure to BIOSTATE across all groups was 8 days, greater in the prophylactic group (range 53-197) compared with major surgery (3-24), minor surgery (1-8) and non-surgical bleeds (1-10). BIOSTATE was shown to be efficacious and well tolerated when treating patients with VWD. This study also provides important insights into dosing regimens with BIOSTATE and the role of monitoring therapy with FVIII:C and VWF:RCo.

Compromised ITAM-based platelet receptor function in a patient with immune thrombocytopenic purpura

BACKGROUND

Receptors on platelets that contain immunoreceptor tyrosine-based activation motifs (ITAMs) include collagen receptor glycoprotein (GP) VI, and FcgammaRIIa, a low affinity receptor for immunoglobulin (Ig) G.

OBJECTIVES

We examined the function of GPVI and FcgammaRIIa in a patient diagnosed with immune thrombocytopenic purpura (ITP) who had unexplained pathological bruising despite normalization of the platelet count with treatment.

METHODS AND RESULTS

Patient platelets aggregated normally in response to ADP, arachadonic acid and epinephrine, but not to GPVI agonists, collagen or collagen-related peptide, or to FcgammaRII-activating monoclonal antibody (mAb) 8.26, suggesting ITAM receptor dysfunction. Plasma contained an anti-GPVI antibody by MAIPA and aggregated normal platelets. Aggregating activity was partially (approximately 60%) blocked by FcgammaRIIa-blocking antibody, IV.3, and completely blocked by soluble GPVI ectodomain. Full-length GPVI on the patient platelet surface was reduced to approximately 10% of normal levels, and a approximately 10-kDa GPVI cytoplasmic tail remnant and cleaved FcgammaRIIa were detectable by western blot, indicating platelet receptor proteolysis. Plasma from the patient contained approximately 150 ng mL(-1) soluble GPVI by ELISA (normal plasma, approximately 15 ng mL(-1)) and IgG purified from patient plasma caused FcgammaRIIa-mediated, EDTA-sensitive cleavage of both GPVI and FcgammaRIIa on normal platelets.

CONCLUSIONS

In ITP patients, platelet autoantibodies can curtail platelet receptor function. Platelet ITAM receptor dysfunction may contribute to the increased bleeding phenotype observed in some patients with ITP.

The impact of information technology on haemophilia care

The past decade has seen an explosion in the use of computers, data programs, hand-held electronic devices and the Internet. How these advances impact on haemophilia management both now and in the future are discussed from the perspective of haemophilia registries, Internet-based electronic haemophilia treatment records, and the potential for haemophilia telehealth.

Collagen platelet receptor polymorphisms integrin alpha2beta1 C807T and GPVI Q317L and risk of ischemic stroke

Several polymorphisms of integrin alpha2beta1 and glycoprotein (GP) VI that may modify platelet-collagen interactions or subsequent signaling have been described. We conducted a case-control study involving 180 stroke patients and 172 controls to determine whether the alpha2 C807T and GPVI Q317L polymorphisms were associated with an increased risk of ischemic stroke. We found no statistically significant differences in the distribution of alpha2 C807T and GPVI Q317L in patients and controls overall or after stratification by etiological subtype. The GPVI 317QQ genotype was found to be over-represented in a subgroup of patients >/=60 years compared to corresponding controls. However, this association did not remain significant after adjustment for other cardiovascular risk factors. Our results do not support a role for the integrin alpha2 C807T and GPVI Q317L polymorphisms in the development of first-ever ischemic stroke. However, larger studies are required to confirm this.

Effects of regular ingestion of black tea on haemostasis and cell adhesion molecules in humans

OBJECTIVE

To assess the effects in humans of regular ingestion of black tea on haemostasis-related variables and cell adhesion molecules.

DESIGN

Twenty-two subjects were recruited from the general population to a randomised-controlled crossover study. Subjects stopped drinking tea, apart from that provided, for the duration of the study. During a 4-week baseline period all subjects drank 5 cups/day (250 ml) of hot water. The effects of 5 cups/day of black tea for 4 weeks were then compared with hot water. Platelet aggregation in response to three doses of collagen and ADP, plasma concentrations of coagulation and fibrinolytic factors (fibrinogen, factor VII, tPA, PAI-1) and plasma concentrations of cell adhesion molecules (soluble P-selectin, E-selectin, ICAM-1, VCAM-1) were assessed twice, one week apart, at the end of each period. Twenty-four hour urinary concentration of 4-O-methylgallic acid (4OMGA), assessed once at the end of each period, was used as a marker of black tea polyphenol intake.

RESULTS

The 24 h urinary excretion of 4OMGA was increased during regular ingestion of black tea in comparison to hot water (P<0.0001). Black tea resulted in lower soluble P-selectin (P=0.01) in comparison to hot water, but did not influence other adhesion molecules. Soluble P-selectin was significantly correlated with mean collagen-stimulated platelet aggregation at baseline (r=0.61, P=0.003), and during regular ingestion of hot water (r=0.70, P<0.0001) and black tea (r=0.51, P=0.01). However, platelet aggregation was not different between the black tea and hot water periods for collagen- or ADP-stimulated aggregation at any dose. Coagulation and fibrinolytic factors were also not different between periods.

CONCLUSIONS

The effect of black tea on soluble P-selectin provides a potential mechanism for cardiovascular benefits of regular ingestion of tea.

SPONSORSHIP

This study was supported by grants from the Tea Trade Health Research Association and the National Heart Foundation of Australia.

Inherited thrombophilia in ischemic stroke and its pathogenic subtypes

BACKGROUND AND PURPOSE

One or more of the inherited thrombophilias may be causal risk factor for a proportion of ischemic strokes, but few studies have addressed this association or the association between thrombophilia and pathogenic subtypes of stroke.

METHODS

We conducted a case-control study of 219 hospital cases with a first-ever ischemic stroke and 205 randomly selected community control subjects stratified by age, sex, and postal code. With the use of established criteria, cases of stroke were classified by pathogenic subtype in a blinded fashion. The prevalence of conventional vascular risk factors; fasting plasma levels of protein C, protein S, antithrombin III; and genetic tests for the factor V Leiden and the prothrombin 20210A mutation were determined in cases and control subjects.

RESULTS

The prevalence of any thrombophilia was 14.7% (95% CI, 9.9% to 19.5%) among cases and 11.7% (95% CI, 7.4% to 17.0%) among control subjects (OR, 1.3; 95% CI, 0.7% to 2.3%). The prevalence of individual thrombophilias among cases ranged from 0.9% (95% CI, 0.1% to 3.4%) for protein S deficiency to 5.2% (95% CI, 0.3% to 9.1%) for antithrombin III deficiency; among control subjects, the prevalence ranged from 1.0% (95% CI, 0.1% to 3.6%) for protein S deficiency to 4.1% (95% CI, 0.2% to 7.8%) for antithrombin III deficiency. There were no significant differences in the prevalence of thrombophilia between cases and control subjects or between pathogenic subtypes of ischemic stroke.

CONCLUSIONS

One in 7 patients with first-ever acute ischemic stroke will test positive for one of the inherited thrombophilias, but the relation is likely to be coincidental rather than causal in almost all cases, irrespective of the pathogenic subtype of the ischemic stroke. These results suggest that routine testing for thrombophilia in most patients with acute ischemic stroke may be unnecessary. Whether the thrombophilias may still be important in younger patients with ischemic stroke or in predicting complications (eg, venous thrombosis) and stroke outcome remains uncertain.

Platelet glycoprotein Ibalpha Kozak polymorphism is associated with an increased risk of ischemic stroke

Platelets are pivotal to the process of arterial thrombosis resulting in ischemic stroke. Occlusive thrombosis is initiated by the interaction of von Willebrand factor (vWf) and platelet glycoprotein (GP) Ibalpha. Three polymorphisms have been described in GP Ibalpha (Kozak T/C polymorphism, variable number of tandem repeats [VNTR], and the human platelet antigen 2a [HPA-2a] [Thr] or HPA-2b [Met] at position 145), each of which may enhance the vWf and GP Ibalpha interaction. This study investigated whether these polymorphisms are candidate genes for first-ever ischemic stroke. A hospital-based case-control study was conducted of 219 cases of first-ever ischemic stroke and 205 community controls randomly selected from the electoral roll and stratified by age, sex, and postal code. The subtypes of stroke were classified, the prevalence of conventional risk factors was recorded, and blood was collected to perform genotyping analysis for Kozak C or T alleles, VNTR, and HPA-2a/b. It was found that the Kozak T/C genotype was over-represented in the stroke group (32.2%) compared with controls (22.8%) (odds ratio [OR], 1.6; 95% confidence interval [CI], 1.03-2.54; P <.03), and the association was still present even after adjusting for conventional risk factors. There was a trend in the increased prevalence of HPA-2a/b in stroke patients (15%) compared with controls (9.9%) (adjusted OR, 1.8; 95% CI, 0.94-3.4; P =.07). No associations were seen with the VNTR polymorphism or with any of the polymorphisms with stroke subtype. It was concluded that the Kozak T/C polymorphism, which is associated with an increase in platelet GP Ibalpha surface expression, is an independent risk factor for first-ever ischemic stroke.

Determination of activated protein C resistance in anticoagulated and lupus positive patients

Clotting-based activated protein C (APC) assays have limitations when testing patients on oral anticoagulant (OA) therapy or with a lupus anticoagulant (LA). Predilution in factor V (FV)-deficient plasma and testing with phospholipid-rich Russell Viper venom (RVV)-based methods have been shown to be the most suitable methods when testing these patient groups, respectively. We evaluated a modified RVV based clotting test (Gradileiden V test; Gradipore, Sydney, Australia) in a large patient cohort and determined its sensitivity to the FV Leiden mutation. We also examined whether normal plasma can be used to dilute plasma from warfarinized patients without compromising sensitivity to the FV Leiden mutation. A total of 1,956 plasmas were studied including congenital protein C (five plasmas), and protein S deficiency (five plasmas), LA (29 plasmas), FV Leiden heterozygote (102 plasmas), and homozygote (five plasmas), warfarin (54 plasmas), standard heparin therapy (37 plasmas) and normal healthy controls (21 plasmas). Molecular analysis was performed on all samples. The effect of FV Leiden concentration on the APC ratio was examined by determining the APC resistance of a homozygous plasma serially diluted in six sources of normal plasma (NP). The relationship was non-linear and dependent on the initial APC ratio of the chosen source of NP. APC resistance was demonstrated in the varying sources of NP in dilutions of 1/4 (25% FV Leiden) to 1/32 (3% FV Leiden). A 1/2 dilution in pooled NP is recommended for patients on OA therapy because the test remains sensitive at levels of 25% FV Leiden and this is the dilution routinely used for other applications in a coagulation laboratory. The effect of a LA on the APC ratio was similarly studied by determining the APC resistance of a homozygous plasma serially diluted in two sources of LA-positive plasma. This relationship was also non-linear and dependent on the initial APC ratio of the LA-positive plasma. APC resistance was demonstrated in dilutions of 1/16 (6% FV Leiden) to 1/64 (1.5% FV Leiden) demonstrating the sensitivity of the test to APC resistance in the presence of a LA. Our results show the modified RVV-based test clearly predicts the presence of factor V Leiden in a large cohort of patients. The method offers advantages when testing patients with a LA and patients receiving warfarin providing a 1/2 predilution step in pooled NP is performed. Pooled NP does not affect the sensitivity of the test to the mutation, is routinely used in coagulation laboratories, and is considerably less expensive than FV-deficient plasma.

Consensus guidelines for warfarin therapy. Recommendations from the Australasian Society of Thrombosis and Haemostasis

The anticoagulant effect of warfarin should be kept at an international normalised ratio (INR) of about 2.5 (desirable range, 2.0-3.0), although a higher level may be better in a few clinical conditions. The risk of bleeding increases exponentially with INR and becomes clinically unacceptable once the INR exceeds 5.0. Warfarin therapy should be continued for around six weeks for symptomatic calf vein thrombosis, and for 3-6 months after proximal deep vein thrombosis (DVT) that occurs after surgery or limited medical illness. Therapy for six months or longer could be considered for DVT occurring without an obvious precipitating factor, proven recurrent venous thromboembolism (VTE), or if there are continuing risk factors. Oral anticoagulants prevent ischaemic stroke in atrial fibrillation (AF). Maximum efficacy requires an INR > 2.0, but some benefit remains at an INR of 1.5-1.9. Patients aged over 75 years are at greatest risk of intracranial bleeding during warfarin therapy for AF, and the target INR may be reduced to 2.0-2.5, or perhaps as low as 1.5-2.0, in such patients. Warfarin should be withheld if it is more likely to cause major bleeding than to protect from stroke (e.g., in young people with isolated AF where the annual baseline risk of stroke is < 1%). In patients with AF, aspirin is less effective than warfarin (much less effective after such patients have had a stroke or transient cerebral ischaemia). In people with prosthetic heart valves, an INR of 2.5-3.5 is probably sufficient for bileaflet or tilting disc valves, but a higher target INR is necessary for caged ball or caged disc valves. The addition of aspirin (100 mg/day) further decreases the risk of embolism but increases the risk of gastrointestinal bleeding.

Association between high homocyst(e)ine and ischemic stroke due to large- and small-artery disease but not other etiologic subtypes of ischemic stroke

BACKGROUND AND PURPOSE

Elevated plasma homocyst(e)ine may be a causal and modifiable risk factor for ischemic stroke, but the results of previous studies have been conflicting. One possible explanation is that homocyst(e)ine may only be associated with certain pathophysiological subtypes of ischemic stroke.

METHODS

We conducted a case-control study of 219 hospital cases with a first-ever ischemic stroke and 205 randomly selected community control subjects stratified by age, sex, and postal code. With the use of established criteria, cases of stroke were classified by etiologic subtype in a blinded fashion. The prevalence of conventional vascular risk factors, fasting plasma homocyst(e)ine levels, vitamin levels, and nucleotide 677 methylene tetrahydrofolate reductase (MTHFR) genotypes were determined in cases and controls.

RESULTS

Increasing homocyst(e)ine was a strong and independent risk factor for ischemic stroke (adjusted OR 2.7, 95% CI 1.4 to 5.1 for a 5-micromol/L increase in fasting plasma homocyst(e)ine from 10 to 15 micromol/L). Compared with the lowest quartile, the highest quartile of homocyst(e)ine was associated with an adjusted OR of ischemic stroke of 2.2 (95% CI 1.1 to 4.2). Mean plasma homocyst(e)ine was significantly higher in cases of ischemic stroke due to large-artery disease (14.1 micromol/L, 95% CI 12.5 to 15.9, P<0.001) and small-artery disease (12.7 micromol/L, 95% CI 11. 4 to 14.1, P=0.004) compared with control subjects (10.5 micromol/L; 95% CI 10.0 to 11.0) but not in cardioembolic or other etiologic subtypes of ischemic stroke. Compared with the lowest quartile of homocyst(e)ine, the upper 3 quartiles were associated with an adjusted OR of ischemic stroke due to large-artery disease of 3.0 (95% CI 0.8 to 10.8) for the second quartile, 5.6 (95% CI 1.6 to 20) for the third quartile, and 8.7 (95% CI 2.4 to 32) for the fourth quartile (P for trend=0.0005). However, despite a clear association between the TT MTHFR genotype and elevated fasting plasma homocyst(e)ine, there was no association between MTHFR genotype and ischemic stroke or subtype of ischemic stroke.

CONCLUSIONS

There is a strong, graded association between increasing plasma homocyst(e)ine and ischemic stroke caused by large-artery atherosclerosis and, to a much lesser extent, small-artery disease, but not cardioembolic or other etiologic subtypes of ischemic stroke. Our results are consistent with the hypothesis that the deleterious effect of high homocyst(e)ine is mediated primarily via a proatherogenic effect.

Familial thrombophilia and the prothrombin 20210A mutation: association with increased thrombin generation and unusual thrombosis

The 20210A prothrombin mutation has recently been associated with an increased risk of venous thrombosis, but the mechanism of the increased thrombotic risk in affected persons has not been elucidated. We report on a thrombophilic family in which the proband presented with cerebral vein thrombosis and homozygosity for the 20210A prothrombin mutation as her only identifiable risk factor for venous thrombosis. Extended genotyping of family members revealed seven other affected, but asymptomatic, first-degree relatives (one A/A homozygote and six G/A heterozygotes). Plasma levels of prothrombin, prothrombin fragments 1 + 2 and thrombin-antithrombin complexes were highest in A/A homozygotes, intermediate in G/A heterozygotes and lowest in those with the G/G homozygous normal genotype, while D-dimer levels were elevated only in A/A homozygotes. Our results suggest that the 20210A prothrombin mutation is associated with activation of coagulation and increased thrombin generation, not only in patients with a past history of thrombosis but also in otherwise healthy asymptomatic persons. In a similar fashion to the homozygous factor V Leiden mutation, patients with the homozygous 20210A prothrombin mutation could be at highest risk of thrombosis, as suggested by our patient who presented with unusual thrombosis.

No association between the 20210 G/A prothrombin gene mutation and premature coronary artery disease

The 20210 G/A prothrombin gene mutation is associated with an increased risk of venous thrombosis but whether there is an association of the mutation with premature coronary artery disease and acute myocardial infarction remains unclear. To further assess the role of the G/A genotype as a risk factor for arterial vascular disease, we performed a case-control study of 644 patients aged less than 50 years with angiographically proven coronary artery disease, 402 of whom had myocardial infarction, and 679 unrelated healthy control subjects aged less than 50 years, randomly selected from the electoral roll. The prevalence of the G/A genotype was 2.5% in patients with coronary artery disease, and 3.2% in control subjects (odds ratio 0.8; 95% confidence interval 0.35 to 1.83). The mutation was not more frequent among patients with a history of myocardial infarction (2.2%, odds ratio 0.7; 95% confidence interval 0.27 to 2.05), and there was no evidence of an interaction between the prothrombin mutation and conventional cardiovascular disease risk factors. There was no association between genotype and extent of angiographic coronary artery disease (p=0.73). We conclude that the 20210 G/A prothrombin gene mutation is not a major risk factor for premature coronary artery disease in our predominantly Caucasian Australian population.

Cross-reactivity to porcine factor VIII of factor VIII inhibitors in patients with haemophilia in Australia and New Zealand

BACKGROUND

Inhibitory antibodies which neutralise factor VIII develop in 10-20% of individuals with inherited haemophilia A and rarely as autoantibodies in normal individuals to cause acquired haemophilia. The antibodies are directed against human factor VIII but cross-react to varying degrees with porcine factor VIII. Porcine factor VIII can be used for treatment in individuals with low cross-reactivity.

AIMS

To determine the cross-reactivity of factor VIII inhibitors between human factor VIII and porcine factor VIII, in a population of patients with inherited and acquired haemophilia A. Also, to determine whether patients with inherited haemophilia and inhibitors have a higher incidence of factor VIII gene inversion in intron 22.

METHODS

Samples and data sheets from 43 patients with inherited and ten with acquired haemophilia were submitted from hospitals in Australia and New Zealand. Inhibitor levels to human and porcine factor VIII were measured by the Bethesda method in 39 with inherited and nine with acquired haemophilia A.

RESULTS

Of 39 patients with inherited haemophilia A, cross-reactivity was 0% in 17 patients, 1-19% in six, 20-39% in 11 and 40-80% in five. In six of nine patients with acquired haemophilia cross-reactivity was < or = 7%. In inherited severe haemophilia A, the frequency of the intron 22 inversion was not greater in 37 study patients than in 28 patients without an inhibitor.

CONCLUSIONS

Many patients in Australia and New Zealand with inhibitors to human factor VIII presently show a low or absent level of cross-reactivity to porcine factor VIII. These may respond to treatment with this concentrate at least in the short term. There remains a group of patients with high cross-reactivity who will respond only to recombinant factor VIIa or prothrombin complex concentrates.

Low-dose combination chemotherapy for acute myeloid leukemia in elderly patients: a novel approach

Eighteen patients aged 60-84 years with acute myeloid leukemia were treated with low-dose combination chemotherapy comprising cytarabine, etoposide, and mitozantrone or 6-thioguanine; seven of these patients had a pre-existing myelodysplastic syndrome. Nine patients achieved a complete remission, and five had a partial remission. The duration of survival in these 14 responding patients has ranged from 2+ to 19+ months. Myelotoxicity occurred regularly, with time to recovery (neutrophils > or =0.5 x 10(9)/L, platelets > or =50 x 10(9)/L) from nadir being 10-14 days in 12 of the 14 patients. This novel approach with an overall response rate of 78% appears to be a simple and effective form of therapy for elderly patients.

Single or duplicate analysis for automated prothrombin time and activated partial thromboplastin time?

The introduction of automated coagulation analysers raises the possibility of performing routine coagulation tests as single rather than duplicate analyses. This study compares the duplicate results of the prothrombin time (PT) and activated partial thromboplastin time (aPTT) to that of a single result obtained by the MLA Electra 1000c using two different methods. The first method looks specifically at the difference between the mean duplicate result and the single result to determine if they alter patient management. This method found that two of 4152 PTs (0.048%) and two of 3047 aPTTs (0.065%) were clinically significant. The second method statistically assessed the agreement between the traditional mean duplicate result and the single test. This supported the introduction of single testing as the calculated 95% confidence intervals demonstrate that each result is interchangeable for purposes of clinical interpretation. These results supported the introduction of single testing for PT and aPTT estimation in our laboratory. The introduction of single testing was accompanied by changes to quality control and machine maintenance to ensure that the functions previously covered by duplicate testing were maintained. A strict protocol for repeat testing has also been adopted.

Hepatitis C genotypes in Australian haemophilia patients

BACKGROUND

Differences in the hepatitis C virus (HCV) genotype influence the severity of HCV related liver disease and response to interferon therapy. HCV infection is frequent in Australian haemophilia patients who have been exposed repeatedly to multiple HCV genotypes through non HCV virally inactivated clotting factor concentrates. The distribution of the various HCV genotypes in Australian haemophilia patients is unknown.

AIM

To examine the HCV genotype distribution and clinical features of HCV associated liver disease in Australian haemophilia patients.

METHODS

Forty patients with bleeding disorders who were known to be both HCV antibody and polymerase chain reaction (PCR) positive were evaluated by direct sequencing of the PCR products for the HCV genotype.

RESULTS

Genotype 1 was found in 65% of patients (26/40), type 2 in 5% (2/40) and type 3 in 30% (12/40). No genotypes 4 to 6 were found. There was no association between the HCV genotype and the severity of haemophilia, alanine transaminase levels, or the presence of portal hypertension. Unlike European, Asian and American studies where the majority of type 1 infection is subclass 1b, in Australian haemophilia patients it is subclass 1a (73%-19/26) which may have a better prognosis and response to interferon.

CONCLUSIONS

Despite patients with haemophilia being exposed to multiple HCV genotypes, it appears that there is no selection advantage of one genotype over another. Australian haemophilia patients with HCV have a different genotype distribution to that reported in other countries and care should be observed in interpreting non Australian studies concerning HCV.

Pure red cell aplasia of pregnancy: a distinct clinical entity

We describe a 31-year-old patient with pure red cell aplasia of pregnancy, successfully managed with regular blood transfusions. In vitro studies showed specific inhibition of day 14 erythroid colonies (BFU-E) using serum and purified immunoglobulin G (IgG) obtained from the patient at diagnosis (before blood transfusion). The inhibition of BFU-E disappeared when haematological remission occurred 3 weeks after delivery and she remains clinically well with a normal haemoglobin 4 years later.

Platelet function in myeloproliferative disorders: characterization and sequential studies show multiple platelet abnormalities, and change with time

Bleeding and thrombosis are well known major causes of morbidity and mortality in patients with myeloproliferative disorders (MPD) but the relationship between these clinical events and the commonly found platelet function abnormalities have not been established. In this study we performed simultaneous laboratory evaluations in 54 patients with MPD to investigate abnormalities in platelet aggregation and cyclooxygenase activity, the latter by using an in vitro aspirin inhibition test; the studies were repeated in 22 patients 1-27 months later. We have found platelet hyper- and hypofunction co-existing in some patients (9/54), and change of platelet function during the course of the disease (7/22) with platelet hypofunction being the only constant abnormality over time. These results may explain the lack of correlation between the clinical events and the limited assessment of platelet function in the hitherto published studies, and also suggest the need for repeated evaluations to properly assess the relative risk for bleeding and thrombosis.

Effect of dibutyryl cyclic AMP on the release of melanocyte-stimulating hormone from rat neurointermediate lobes in vitro

A method for measuring melanocyte-stimulating hormone (MSH) in rat neurointermediate lobe in vitro and in incubation medium, using polyacrylamide gel electrophoresis, is described. Using this technique, it was shown that dibutyryl cyclic AMP increased the release of MSH in vitro, the degree of stimulation depending on the concentration of the nucleotide. The effect of low concentrations of the nucleotide was potentiated by theophylline.