Identification of a thrombin-interactive site within the FVIII A2 domain that is responsible for the cleavage at Arg372

FVIII is activated by cleavage at Arg³⁷², Arg⁷⁴⁰, and Arg¹⁶⁸⁹ by thrombin. This study showed that an anti-A2 monoclonal antibody, with a specific epitope for residues 484–509, and anti-FVIII inhibitor alloantibodies with similar A2 epitopes, inhibited thrombin-catalyzed FVIII activation. Sodium dodecyl sulphate polyacrylamide gel electrophoresis analysis showed that cleavage at Arg³⁷² but not at Arg⁷⁴⁰ occurred at approximately fourfold decreased rate in the presence of anti-A2 antibody. Peptide 484–509 also inhibited co-factor activation, consistent with inhibition of cleavage at Arg³⁷². Direct binding studies using active-site modified thrombin showed that a 484–509 peptide as well as the anti-A2 antibodies blocked the A2-thrombin binding. Furthermore, covalent cross-linking was observed between the 484–509 peptide and thrombin following reaction with 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide. Mutant A2 molecules in which the clustered basic residues in this sequence were converted to alanine were used to assess the binding reactions in a surface plasmon resonance-based assay. Mutants R484A, R489A, R490A, H497A and K499A possessed two to fivefold lower affinity than wild-type A2. These findings demonstrate that clustered basic residues within the 484–509 region of the A2 domain play a part of key role in thrombin-binding, which is responsible for thrombin-catalyzed FVIII activation by cleavage at Arg³⁷².     

Factor VIII gene analysis in Japanese CRM-positive and CRM-reduced haemophilia A patients by single-strand conformation polymorphism

Haemophilia A is the most common X-linked blood coagulation disorder; it is caused by deficiency of factor VIII activity (FVIII:C). Half of the affected patients do not have detectable levels of FVIII protein in their plasma, whereas about 5% have normal levels of the FVIII antigen (FVIII:Ag) (> 50 u/dl), and are called cross-reacting material (CRM) positive (CRM⁺ or A⁺). About 45% of patients have reduced levels of the FVIII:Ag (1–50 u/dl), classified as CRM reduced (CRM^R or A^R). We screened the FVIII gene of 13 Japanese patients (five CRM⁺ and eight CRM^R) by single-strand conformation polymorphism, and identified 11 different mutations in 13 patients by analysing all 26 exons (Trp255Cys, Tyr473Cys, Gly479Arg, Arg531His, Thr667Arg, Arg1689Cys, Arg1941Gln, Arg2150His, Arg2159Cys, Thr2245Ala and Gly2285Val). Seven mutations were identified in the A domains (four in the A2 domain). All the mutations are point mutations resulting in missense codons. Four mutations (Trp255Cys, Thr667Arg, Thr2245Ala and Gly2285Val) have not been described previously.     

Pharmacokinetics of recombinant factor VIII (Kogenate-FS®) in children and causes of inter-patient pharmacokinetic variability

Summary.  Understanding the pharmacokinetics (PK) of factor VIII (FVIII) is important in the management of patients with haemophilia A. We studied the PK of FVIII in order to determine aetiological factors contributing to PK variability of FVIII in children.
Twenty children with haemophilia A (mean age 12.8 years) were administered a single bolus of 50 U kg⁻¹ of recombinant FVIII (rFVIII; Kogenate-FS^®, Bayer).
The mean incremental FVIII recovery was 1.87 (U mL⁻¹)/(U kg⁻¹) (range: 1.25–2.76) and the mean FVIII half-life was 10.7 h (range: 7.8–15.3). FVIII recovery was positively correlated with body surface area (BSA; P  = 0.04). FVIII half-life was positively correlated with preinfusion levels of von Willebrand factor antigen (VWF:Ag) ( P  = 0.0001) and was reduced in patients ( n  = 6) with very low FVIII inhibitor titres (<0.5 BU) vs. those ( n  = 14) with negative inhibitor titres ( P  = 0.06).
These observations suggest that (i) young children with haemophilia in comparison with adults have a low recovery of FVIII and that this might be explained by differences in body composition (BSA, plasma volume), (ii) levels of VWF:Ag may explain some of the differences in the half-life and clearance of FVIII and (iii) very low inhibitor titres, previously regarded as clinically insignificant, may actually be significant and should be evaluated in the context of PK studies.     

An arginine to cysteine amino acid substitution at a critical thrombin cleavage site in a dysfunctional factor VIII molecule

We have analyzed the factor VIII (FVIII) protein and the nucleotide sequence around two thrombin cleavage sites, at arginine 372 in the FVIII heavy chain and arginine 1689 in the FVIII light chain in a naturally occurring dysfunctional FVIII variant, FVIII Okayama. The patient was a 42-year-old hemophiliac with a FVIII coagulant activity of 0.03 U/mL and a FVIII antigen level of 0.8 U/mL. The patient's FVIII was not thrombin activatable to levels seen in normal plasma. Immunoblotting of partially purified FVIII Okayama and normal FVIII showed that thrombin cleavage of the 92 kilodalton (Kd) heavy chain was impaired in the mutant protein. The patient's genomic DNA was amplified using the polymerase chain reaction with two sets of synthetic oligonucleotide primers spanning amino acid residues 319 to 400 and 1630 to 1720. Sequence analysis of the amplified DNA fragments revealed a cytosine to thymine transition, converting an arginine to a cysteine codon at residue 372. No abnormality was found in the FVIII light chain region analyzed. The patient's hemophilic brother and carrier mother revealed the same mutation. We conclude that the pathogenesis of hemophilia A in this patient is probably due to an arginine to cysteine substitution at a thrombin cleavage site in the FVIII heavy chain.     

Thrombin generation and platelet activation induced by rFVIIa (NovoSeven®) and NN1731 in a reconstituted cell-based model mimicking haemophilia conditions

Summary.  Replacement therapy with factor VIII (FVIII) and factor IX (FIX) is routinely used in haemophilia patients with haemophilia A and B, respectively, while recombinant activated FVII (rFVIIa) has proven to induce haemostasis in haemophilia patients with inhibitors. To evaluate the effect of therapeutic intervention in patients with residual factor activities, the effects of increasing concentrations of rFVIIa or NN1731 on thrombin generation and platelet activation were measured in a cell-based model system mimicking severe, moderate and mild haemophilia A or B. Purified monocytes stimulated to express tissue factor and non-activated platelets from peripheral blood of healthy donors were incubated with a mixture of purified human coagulation factors in the absence or presence of increasing concentrations of FVIII or FIX. Sub-samples were analysed for thrombin activity and platelet activation measured as exposure of P-selectin by flow cytometry. Dose-dependent increases in thrombin generation and platelet activation were observed following increasing concentrations of rFVIIa or NN1731 in both haemophilia A- and B-like conditions. At 25 n m rFVIIa, which nears the peak levels in patient plasma after 90 μg kg⁻¹ intravenous dosing, the effects on maximum thrombin generation rate (maxTG) at 1–10% FVIII were comparable to those at 100% and 200% FVIII in the absence of rFVIIa. Normalization of maxTG required 500 n m rFVIIa and 25 n m NN1731 or 25–100 n m rFVIIa and 5 n m NN1731 in severe or moderate/mild haemophilia A and haemophilia B, respectively. This suggests that NN1731 holds its promise as a future bypassing agent for haemophilia patients with and without inhibitors.     

Potency and mass of factor VIII in FVIII products

Summary.  Several factor (F) VIII products of different origin and structure are being used for haemophilia A treatment worldwide. The assessment of FVIII concentration in these products is done using activity assays, which are dependent upon the assay and its modifications. To evaluate FVIII products for potency and for FVIII concentration and specific activity, three activity-based assays [activated partial thromboplastin time (APTT), intrinsic FXase and synthetic coagulation proteome] and two immunoassays (ELISA and western blotting) were used in this study with albumin-free full-length recombinant (r) FVIII as a standard. In all activity assays, products A and B (both contain full-length rFVIII) at 1 U mL⁻¹ showed potency similar to that of the 0.7 n m (1 U mL⁻¹) rFVIII standard. Product E (contains truncated rFVIII) was less potent in the APTT (83% of standard) and product C (contains plasma FVIII) was less potent in FXase assays (66%). The ELISA immunoassay revealed that the specific activity of FVIII proteins in products A–C and E varied over a wide range (3900–13 200 U mg⁻¹) and was higher for most lots when compared with the standard (5000 U mg⁻¹), whereas the specific activity of product D (contains plasma FVIII) was lower than expected (3200–4800 U mg⁻¹). (i) FVIII potency estimated in different assays gives dissimilar results; (ii) the specific activity of FVIII in various FVIII products is different and inconsistent. Thus, the administration of an equal FVIII potency in units means the administration of different amounts of FVIII protein, which may partly explain apparent discrepancies in product performance.     

Purification and characterization of factor VIII 372-Cys: a hypofunctional cofactor from a patient with moderately severe hemophilia A

We have purified factor VIII from a patient with moderately severe hemophilia A (FVIII, 4 U/dL; FVIII:Ag, 110 U/dL) and subjected the protein to Western blot analysis after time course activation with thrombin. The cross reacting material-positive (CRM+) FVIII has the normal distribution of heavy and light chains before thrombin activation, and, after incubation with the enzyme, appropriate cleavages are made at positions 740 and 1689. However, the normal thrombin cleavage at position 372 in the heavy chain of this molecule does not occur. This result is consistent with the demonstration in the patient's leukocyte DNA of a C to T transition in codon 372, leading to the substitution of a cysteine for an arginine residue at the heavy chain internal cleavage site. The severely impaired functional activity of this molecule confirms that the heavy chain of FVIII must be proteolysed in order to effect full cofactor activation in vivo. However, a threefold activation was detected when this protein was incubated with thrombin. No evidence of thrombin-mediated cleavage at position 336 in the heavy chain was detected, in contrast to the variant recombinant B domainless-molecule, FVIII 372-Ile, described by Pittman and Kaufman (Proc Natl Acad Sci USA 85:2429, 1988). Using gel permeation studies of the FVIII/von Willebrand factor (vWF) complex before and after thrombin activation, we have demonstrated that the 40 Kd A2 domain of wild type FVIII dissociates from vWF after cleavage by the enzyme. In contrast, incomplete dissociation was detected in the case of FVIII 372-Cys. We conclude that the functional defect in FVIII 372-Cys is a consequence of the resistance to proteolysis of the internal scissile bond in the heavy chain.     

Thrombin generation in vitro in the presence of by-passing agents in siblings with severe haemophilia A

Summary.  Previous data have shown an inter-individual difference in the thrombin generating capacity in vitro as well as phenotypic bleeding pattern among patients with severe haemophilia A (FVIII:C activity below 1%). The reason for this is not known. In addition, there are no reports on how thrombin generation may correlate between siblings. In this study, we evaluated and compared thrombin generation in vitro using plasma samples in the presence of by-passing agents (FEIBA^® and NovoSeven^®) in 21 unrelated brother pairs with and without inhibitors enrolled in the Malmö International Brother Study (MIBS). Mean maximum thrombin formation in patients with a current inhibitor titer was 182.0 ± 52.8 mmol mL⁻¹ (FEIBA^®) and 130.7 ± 54.9 mmol mL⁻¹ (rFVIIa), respectively, and somewhat higher in those without inhibitors, 222.7 ±85.5 mmol mL⁻¹ (FEIBA^®) and 142.8 ±53.6mmol mL⁻¹ (rFVIIa) ( P  = 0.16 and 0.29). The variance regarding the maximum thrombin production within a family was significantly lower compared with the thrombin production between families ( P  < 0.001 for both FEIBA^® and NovoSeven^®). Our data indicate that genetically determined factors, other than the FVIII:C activity seems to influence the phenotypic variation in thrombin formation in the presence of by-passing agents. The nature of these determinants remains to be identified.     

Common inhibitory effects of human anti-C2 domain inhibitor alloantibodies on factor VIII binding to von Willebrand factor

Summary. Factor VIII (FVIII) Inhibitor alloantibodies obtained from seven severe haemophilia A patients were examined for their binding regions and their effects on FVHI binding to von Willebrand factor (vWF). Immunoblotting analysis with a panel of recombinant fragments demonstrated that the binding regions of antibodies in cases 1-5 were contained in the C2 domain of the light chain. Antibodies from cases 1 and 2, which recognized an epitope within residues 2248-2312, completely inhibited FVIII/ vWF binding in an FXISA (IC₅₀: 5-0 and 9-0μg/ml, respectively). Antibodies from case 3 recognizing 2170-2312 and case 5 recognizing 2170-2327 also inhibited FVIII/vWF binding (IC₅₀:110 and 400μg/mI, respectively). Case 4 antibodies recognizing 2218-2307 showed barely detectable inhibition and cases 6 and 7 antibodies recognizing the 44 kD heavy chain, did not inhibit. Our results demonstrate that all anti-C2 alloantibodies with epitopes that extend to the residue 2312 inhibit vWF binding and that an overlap of the inhibitor epitope with residues 2308-2312 is critical for maximal inhibition of vWF binding. Prevention of FVIII/vWF binding appears to be a common property of anti-C2 domain inhibitor alloantibodies.     

Performance of recalibrated ReFacto® laboratory standard in the measurement of FVIII plasma concentration via the chromogenic and one-stage assays after infusion of recalibrated ReFacto® (B-domain deleted recombinant factor VIII)

Summary.  The use of ReFacto Laboratory Standard ( RLS ) in the one-stage clotting assay was proposed to reduce the underestimation of factor VIII (FVIII) plasma concentration after the infusion of 'ReFacto^®' (B-domain deleted recombinant FVIII) in haemophilia A patients. Both ReFacto^® and RLS were recently recalibrated, with the resulting materials containing approximately 20% more protein than the previous products. The aim of this study was to evaluate the performance of recalibrated RLS in the measurement of FVIII plasma concentration after the infusion of recalibrated ReFacto^®. In 13 severe haemophilia A patients, 25 IU kg⁻¹ of ReFacto ^® were injected intravenously. Venous blood samples were collected at 0.25, 0.5, 1, 3, 6, 9, 24, 28 and 32 h after the end of the infusion. Pharmacokinetic parameters were measured for the chromogenic and one-stage assays using International Plasma Standard (IPS) and RLS for both assays and assuming a non-compartmental drug disposition. Comparisons among assays and standards were performed using anova . Pharmacokinetic estimates obtained with the chromogenic method were in agreement with those published in the literature. The one-stage method was confirmed to be more sensitive to lower plasma concentrations of FVIII. The measured maximum plasma concentration ( C _max ) was slightly higher than theoretical values and independent of the assay used. C _max , area under the curve ( AUC) and volume of distribution at steady state ( V _ss ) presented non-significant differences among the methods and standards used. The clinical utility of RLS in the evaluation of FVIII concentration after the infusion of ReFacto^® seems to be reduced since recalibration of the product.     

Precipitating anti-VIII:C antibodies in two patients with haemophilia A

S ummary . IgG from the plasmas of two haemophilia A patients with anti-VIII:CAg antibodies (1000 and 200 u/ml) was isolated and labelled with ¹²⁵I. The specific labelled anti-VIII:CAg IgG was further purified by binding to and elution from immobilized factor VIII/von Willebrand factor (F.VIII/vWF). When studied by immunodiffusion and autoradiography, both antibodies gave a precipitin line with normal plasma, serum, cryoprecipitate, purified F.VIII/vWF and the plasmas of two patients with haemophilia A⁺. No precipitin line was observed with the plasmas of 11 patients with haemophilia A⁻ or four patients with severe von Willebrand's disease. Levels of VIII:CAg obtained by radioelectroimmunoassay were in agreement with those obtained by immunoradiometric assay. This study demonstrates that, contrary to previous evidence, human anti-VIII:CAg antibodies are precipitating as well as neutralizing when studied by highly sensitive techniques.     

Pharmacokinetics of von Willebrand factor and factor VIII coagulant activity in patients with von Willebrand disease type 3 and type 2

Nine patients with von Willebrand disease type 3, six with type 2B, one with type 2A, and one patient with type 1/2N were infused with one dose of ≈50 or 100 IU ristocetin cofactor activity (RCoF) per kg body weight of von Willebrand factor (vWF) (Human), a product with a very low content of factor VIII (FVIII). Blood samples were collected over 96 h. The data for RCoF and vWF antigen (vWF:Ag) were fitted to a 1-compartment model decay. The data for FVIII:C were fitted to a model with a linear time 'synthesis' term and a 1-compartment decay. Results in von Willebrand disease type 3 patients (nine patients; 10 infusions) indicated a volume of distribution of 39.9 and 39.8 mL kg⁻¹ for RCoF and vWF:Ag, respectively. The FVIII:C rate of synthesis was 6.4 U dL⁻¹ h⁻¹ (range: 4.4–8.8). The decay rates for FVIII:C, RCoF, and vWF:Ag were 0.041 (h⁻¹) [ t _1/2: 16.9 h]; 0.061 (h⁻¹) [ t _1/2: 11.3 h] and 0.006 (h⁻¹) [ t _1/2: 12.4 h], respectively. In patients with von Willebrand disease type 2 ( n  = 8) the RCoF mean volume of distribution was 46 mL kg⁻¹. The factor VIIIC mean rate of synthesis was 5.5 U dL⁻¹h⁻¹ and the decay rate 0.043 (h⁻¹) [ t _1/2: 16.1 h]. The rate of decay for RCoF and vWF:Ag were 0.050 (h⁻¹) [ t _1/2: 13.9 h] and 0.044 (h⁻¹) [ t _1/2: 15.7 h], respectively.     

In vitro and in vivo stability of diluted recombinant factor VIII for continuous infusion use in haemophilia A

Summary.  Factor VIII (FVIII) replacement by continuous infusion (CI) is used postoperatively or after significant bleeding. For young paediatric patients, CI may require FVIII dilution. Variable stabilities of diluted full-length recombinant FVIII Kogenate^® FS (KG-FS) have been reported under different storage conditions. We investigated the recovery and stability of diluted KG-FS in vitro and in vivo . Kogenate^® FS was diluted to 50–120 U mL⁻¹ and its recovery and stability in glass vials or polypropylene syringes was determined. Furthermore, stability of KG-FS diluted to 80 U mL⁻¹'administered' via single- and double-pump mock CI systems was tested. Finally, the in vivo stability of KG-FS diluted to ∼60 U mL⁻¹ and administered postsurgically by CI with the double-pump to a paediatric patient with severe haemophilia A undergoing implantable venous access device placement was investigated. Initial KG-FS dilution resulted in a 10–20% FVIII loss; a further 25–30% loss occurred over 72 h in vials or syringes. With the double-pump, 1 h recovery was 35%, increasing to 80% by 24 h; the initial losses were because of the Y-infusion of a 10-fold larger volume of saline concomitantly with the FVIII. In vivo , CI resulted in stable FVIII activity levels within the target range. These in vitro results are important for the generation of CI guidelines for diluted KG-FS in the paediatric haemophilic population. That FVIII losses occur upon dilution and with the double-pump does not preclude use of diluted KG-FS. Indeed, stable FVIII levels were maintained when diluted KG-FS was administered by CI with the double-pump to a paediatric patient postsurgically.     

Absence of mutations at the activated protein C cleavage sites of factor VIII in 125 patients with venous thrombosis

Resistance to activated protein C (APC), caused by a mutation at amino acid position Arg⁵⁰⁶ of the factor V gene, has recently been identified as the most prevalent genetic defect associated with venous thrombosis. Similarly to factor V, mutations at the cleavage sites of factor VIII for APC may occur in patients with venous thrombosis. Here we have analysed 125 consecutive patients with incidental or recurrent venous thromboembolism for the presence of mutations at the cleavage sites for APC at amino acid positions Arg³³⁶ and Arg⁵⁶² of factor VIII. Our findings indicate that mutations at these amino acid positions of factor VIII do not occur in the patient group analysed.     

Immunotoxins containing saporin linked to different CD2 monoclonal antibodies: in vitro evaluation

In this study we describe immunotoxins prepared with different CD2 monoclonal antibodies (mAbs) and a ribosome-inactivating protein, saporin. The CD2 immunotoxins were tested on different models. Anti-CD2–saporin conjugates inhibited protein synthesis by a neoplastic CD2+ cell line (SKW-3) and by an interleukin 2 dependent polyclonal CD2+ lymphoid cell culture (T lymphoblasts), with IC₅₀s ranging from 10^-13 m to 10^-11 m (as saporin). Similar results were obtained with proliferation inhibition tests (³H-thymidine incorporation) on phytohaemagglutinin (PHA) driven lymphoid cultures and on mixed lymphocyte culture activated lymphocytes. Moreover a CD2–ricin A chain conjugate was less effective than an analogous immunotoxin containing the same CD2 mAb and saporin in inhibiting lymphocyte proliferation induced by PHA (IC₅₀ approximately 10^-9 m as ricin A chain versus 10^-12 m as saporin). The conjugates were not toxic on bone marrow stem cells. These results suggest that CD2–saporin immunotoxins could represent an effective tool for CD2+ lymphomas or leukaemias, and for T-dependent immune disorders, such as transplanted organ rejection and graft-versus-host disease.     

Haemostatic treatment in connection with surgery in patients with von Willebrand disease

Haemostatic treatment in patients with von Willebrand disease (vWD) in connection with surgery aims at normalizing the haemostatic defect in order to avoid bleeding complications. Factor VIII (FVIII) levels in plasma must be normalized in connection with major surgery, whereas the bleeding time is more important for mucous membrane bleedings. Most patients respond well to treatment with desmopressin which stimulates the endogenous release of FVIII and von Willebrand factor (vWF) and shortens the bleeding time. Non-responders to desmopressin are substituted with a plasma-derived factor concentrate which contains vWF and FVIII. This paper includes a summary of retrospective data from the last 10 years on haemostatic treatment in connection with surgery from four haemophilia centres in Sweden and Denmark on 40 invasive procedures in 27 vWD patients and on one normal delivery. If a FVIII-containing concentrate is given prior to surgery a dose of 30–40 IU VIII:C kg⁻¹ will normalize FVIII levels in most severe cases. If a pure vWF concentrate is used, a dose of 40–50 IU RCoF kg⁻¹ will normalize RCoF in most cases, but FVIII levels will not be normalized until after about 12 h or later. Repeated doses of FVIII-vWF concentrate may lead to very high levels of FVIII in plasma because of the combined effect of the exogenous FVIII-substitution and the endogenous FVIII-release induces by the infused vWF. Dosage should be adjusted according to FVIII levels in plasma.     

Von Willebrand factor protects the Ca2+-dependent structure of the factor VIII light chain

We have recently reported that cation-exchange iminodiacetate resin completely inactivated factor VIII (FVIII) by direct deprivation of metal ions, predominantly Ca²⁺, from its molecules, and that von Willebrand factor (VWF) protected FVIII antigen from resin-induced degradation. The present study was further developed to investigate this mechanism. Western blotting analysis and enzyme-linked immunosorbent assay showed that the antigenic structure of the FVIII light chain, especially the C2 domain, was completely impaired by the resin, whilst that of the heavy chain was little affected. However, the complex formation with VWF protected the C2 domain from the resin-induced degradation. The resin-treated C2 domain failed to interact with VWF and phospholipid. Furthermore, the addition of Ca²⁺ competitively blocked the resin-induced impairment of the C2 domain structure. These results demonstrate that VWF protects the Ca²⁺-dependent conformational structure of the FVIII light chain, especially the C2 domain, and may indicate that the C2 domain contains the Ca²⁺-binding site(s).     

Phosphatidylserine surface expression and integrin αIIbβ3 activity on thrombin/convulxin stimulated platelets/particles of different sizes

Platelets stimulated by a combination of thrombin/convulxin have been shown to develop two to three populations characterized by different phosphatidylserine (PS) surface expression and integrin αIIbβ3 activity. To determine how these markers are distributed on the surface of platelets/particles, we studied Annexin V and PAC-1 binding to platelets/particles of different sizes by flow cytometry analysis and evaluated influences of calpain and caspase inhibitors on thrombin/convulxin-activated platelets. Analysed platelets/particles were divided by their sizes, according to the standard size beads, into seven populations from 0·37 to 4·8 μm. PAC-1 binding/μm² was almost equal in platelets/particles ranging from 1·2 to 4·8 μm and was significantly lower on smaller-sized particles sizes (0·37–0·7 μm). PS surface exposure/μm² was high in the particles of 0·37–1·2 μm and very low in platelets (2·6–4·8 μm). Upon thrombin/convulxin stimulation caspase inhibitors prevented microparticle (MP) formation, while a calpain inhibitor stimulated MP formation. It was also shown that stimulated platelets are heterogeneous not only in their ability to activate αIIbβ3 integrin complex and expose PS on their surface, but also in the distribution of activation markers, which strongly depends on platelet/particle size and that platelets/particles of different sizes provide different responses to the same stimulus.     

Variability of the factor VIII response to DDAVP in a large kindred with mild haemophilia A

Since 1977, desmopressin acetate (DDAVP) has established its important role in the clinical management of bleeding in milder cases of von Willebrand's disease and haemophilia A. We present in vivo DDAVP response data from a large kindred suffering from mild haemophilia A. Levels of FVIII: C in 22 affected family members ranged from 0.11 to 0.24 IU mL⁻¹ of FVIII: C (0.18 ± 0.04, mean ± SD), increasing to 0.22–0.92 IU mL⁻¹ after DDAVP, giving a mean response ratio of 3.5. Response rates by various routes of administration did not differ significantly, being 3.3 for subcutaneous administration ( n = 17), 3.7 for intravenous administration ( n = 4) and 3.2 for intranasal spray application ( n = 1). No significant correlation was found between the pretreatment level and the response rate. In three individuals, the post-DDAVP level of FVIII:C was below 0.40 IU mL⁻¹, the value we arbitrarily regard as the lower limit of a successful response for haemostatic efficacy suited for self-management purposes, demonstrating that the response rate in a given member of the family cannot be predicted from previous experiences with other haemophilic members of the same subset.     

A1,2BO1,2 genotyping by multiplexed allele-specific PCR

The ABO blood group is the most clinically important human alloantigen system in transfusion medicine. The system involves three antigens A, B and H. H antigen is converted to either A or B by the activity of α1 → 3- n -acetyl-galactosaminyl transferase (A transferase) or α1 → 3 galactosyl transferase (B transferase). The O phenotype is the result of an inactive glycosyltransferase, which is unable to glycosylate the H antigen.
The immunological properties of the ABO system were identified at the turn of the century; however, the genetic basis of the ABO system has only recently been characterized. This has enabled the development of a number of molecular ABO typing methods. Described here is a two-reaction multiplex allele-specific PCR (ASPCR) genotyping assay for the A¹, A², B, O¹ and O² subtypes. 11 different allele-specific oligonucleotide primers were selected to detect the presence or absence of the O¹ associated G →  (−) deletion at base 261, the O² associated G → A substitution at base 802, the B associated G → A substitution at base 803, and finally the A² associated C → (−) deletion at base 1059.
A total of 122 peripheral blood samples were genotyped and serologically forward and reverse typed. A concordance rate of 98.4% (120/122 samples) was observed between the actual genotype and the serologically-based predicted genotype. These results indicate that this assay provides a rapid, accurate, and simple method for A^1,2BO^1,2 genotyping that serves as a useful supplement to standard serological ABO typing.