An investigation of three patients with Christmas disease due to an abnormal type of factor IX

Reclassifying hemophilia to include the definition of outcomes and phenotype as new targets

Hemophilia is classified into mild, moderate, and severe based on coagulation factor activity levels. Factor replacement and prophylaxis regimens in persons with hemophilia have helped to reduce bleeding and its related complications. With several newer treatments, some already approved and others soon to be, there may be a need to consider health-related quality of life in addition to bleed prevention as the goals of providing comprehensive care to persons with hemophilia. In this article, we discussed the reasons why such an approach may be relevant and call for the International Society of Thrombosis and Haemostasis to revisit the current classification of hemophilia.

Factor X Friuli Coagulation Disorder: Almost 50 Years Later

The story of factor X (FX) Friuli. Factor X Friuli was discovered in 1969 to 1970. However, the story of that disease was an international event since patients with this defect were studied in France and in Italy, and different diagnoses were reached-FVII; FX; combined prothrombin complex; and combined FII, FVII, and FX deficiencies. The diagnostic difficulties were due to the peculiar clotting pattern presented by these patients, namely, prolonged partial thromboplastin time, prolonged prothrombin time but normal Russell viper venom clotting time. Only suitable anti-FX antisera clarified the pattern. Altogether 12 homozygotes and 102 heterozygotes have been followed during 4 decades. Six homozygotes died, 2 of them due to HIV infection and 1 due to hepatitis B liver cirrhosis. The other 3 died of nontransfusion-related morbidity. Bleeding tendency has been moderate in agreement with the extrinsic or intrinsic system assay results-FX level of 4% to 5% is considered normal. Heterozygotes may present occasional bleeding manifestations usually during surgery or delivery. Molecular analysis have shown that the mutation responsible for the defect is a Pro343Ser substitution in exon 8. Chimeric FX Friuli mice have been useful in studying the effect of FX levels on embryonic or natal mortality of these animals. No new homozygote but several heterozygotes have been recently seen. The study of FX Friuli has revolutionized the diagnostic approach to FX deficiencies. The FX should be assayed by all assay systems. The FX Friuli has never been described in any other country, and all patients studied come from the Friuli Meduna River Valley.

Considerations on a tentative classification of FVII deficiency suited for practical clinical purposes

Adequate classifications of disorders are of paramount importance in the management of congenital bleeding disorders. Classification of congenital FVII deficiency should be simple, based on few tests using thromboplastins of different origin. The first thromboplastin to be used is a rabbit brain preparation since it has been proven that this is the one that, overall, yields the lowest activity level. This is particularly so since molecular biology techniques have supplied important information with regard to the structure-function relation but have failed to supply a satisfactory classification of the defect. Mutations in the same domain have yielded different forms of FVII deficiency. Furthermore, molecular biology techniques are time consuming and are not feasible in every laboratory. A classification of FVII deficiency based on clinical, clotting, and immunological assays is proposed. This classification is suited for practical clinical purposes and may represent a useful preparatory basis for molecular biology studies.

Comparison of the behavior of normal factor IX and the factor IX Bm variant Hilo in the prothrombin time test using tissue factors from bovine, human, and rabbit sources

A subset of hemophilia B patients have a prolonged bovine-brain prothrombin time. These CRM+ patients are classified as having hemophilia Bm. The prolongation of the prothrombin time has been reported only with bovine brain (referred to as ox brain in some literature) as the source of thromboplastin; prothrombin times determined with thromboplastin from rabbit brain or human brain are not reported to be prolonged. Factor IX from a hemophilia Bm patient (factor IX Hilo) was isolated. The activity of factor IX Hilo was compared to that of normal factor IX in prothrombin time assays when the thromboplastin source was of bovine, rabbit, or human origin. Factor IX, either normal or Hilo, prolonged a prothrombin time regardless of the tissue factor source. However, unless thromboplastin was from a bovine source, this prolongation required high concentrations of factor IX. Further, factor IX normal was as effective as factor IX Hilo in prolonging the prothrombin time when rabbit or human thromboplastin was used. With bovine thromboplastin, factor IX Hilo was significantly better than factor IX normal at prolonging the prothrombin time. The amount of prolongation was dependent on the amount of factor IX Hilo added. In addition, the prolongation was dependent on the concentration of factor X present in the sample. The prothrombin time changed as much as 20 seconds when the factor X concentration was varied from 50% to 150% to normal (fixed concentration of factor IX Hilo). These results demonstrate the difficulty of classifying the severity of a hemophilia Bm patient based on the bovine brain prothrombin time unless both the factor IX and factor X concentrations are known.

Identification of a new haemophilia BM case produced by a mutation located at the carboxy terminal cleavage site of activation peptide

We describe a novel point mutation due to C----G transversion at nucleotide 20518 in the exon VI of factor IX gene, resulting in the substitution of glycine (GGG) for arginine (CGG) at position 180 in the polypeptide. This point mutation was found in a patient with a haemophilia BM variant. We designated the altered factor IX produced by this new mutation as factor IXMadrid. This mutation blocks the cleavage site involved in the release of the activation peptide at Arg180-Val181. It also abolishes the Aval site (CTCGGG) in exon VI, which can be directly detected with the enzymatic DNA amplification technique (PCR) and offers the possibility of direct analysis in carrier and prenatal diagnosis in kindreds with this mutation.

Replacement of isoleucine-397 by threonine in the clotting proteinase factor IXa (Los Angeles and Long Beach variants) affects macromolecular catalysis but not L-tosylarginine methyl ester hydrolysis. Lack of correlation between the ox brain prothrombin time and the mutation site in the variant proteins

Previously, from the plasma of unrelated haemophilia-B patients, we isolated two non-functional Factor IX variants, namely Los Angeles (IXLA) and Long Beach (IXLB). Both variants could be cleaved to yield Factor IXa-like molecules, but were defective in catalysing the cleavage of Factor X (macromolecular substrate) and in binding to antithrombin III (macromolecular inhibitor). In the present study we have identified the mutation of IXLA by amplifying the exons (including flanking regions) as well as the 5' end of the gene by polymerase-chain-reaction (PCR) method and sequencing the amplified DNA by the dideoxy chain-termination method. Comparison of the normal IX and IXLA sequences revealed only one base substitution (T----C) in exon VIII of IXLA, with a predicted replacement of Ile-397 to Thr in the mature protein. This mutation is the same as found recently for IXLB. The observation that IXLB and IXLA have the same mutation is an unexpected finding, since, on the basis of their ox brain prothrombin time (PT, a test that measures the ability of the variant Factor IX molecules to inhibit the activation of Factor X by Factor VIIa-tissue factor complex), these variants have been classified into two different groups and were thought to be genetically different. Our observation thus suggests that the ox brain PT does not reflect the locus of mutation in the coding region of the variant molecules. However, our analysis suggests that the ox brain PT is related to Factor IX antigen concentration in the patient's plasma. Importantly, although the mutation in IXLA or IXLB protein is in the catalytic domain, purified IXaLA and IXaLB hydrolyse L-tosylarginine methyl ester at rates very similar to that of normal IXa. These data, in conjunction with our recent data on Factor IXBm Lake Elsinore (Ala-390----Val mutant), strengthen a conclusion that the peptide region containing residues 390-397 of normal Factor IXa plays an essential role in macromolecular substrate catalysis and inhibitor binding. However, the two mutations noted thus far in this region do not distort S1 binding site in the Factor IXa enzyme.

Determination of factor IX allotypes for carrier identification in haemophilia B

The existence of two genetic variants (allotypes) of normal human factor IX is used for carrier detection in three families with severe and one with mild haemophilia B. By analysis of IX:Ag with two different monoclonal antibodies in 93 members of the families, allelic assignment is shown to be a complement in carrier diagnosis to genotypic DNA studies. Allelic assignment makes possible a reliable diagnosis based on phenotypic studies, though its usefulness is limited due to ethnic variation in allelic frequency. Determination of factor IX allotypes should be useful for carrier detection in many Swedish families with haemophilia B.

Two allotypes of factor IX present in haemophilia B

Factor IX antigen (IX:Ag) was measured with three different immunoradiometric assays (IRMAs) in 30 healthy people and 43 patients with haemophilia B of varying severity. Two of the IRMAs were based on monoclonal antibodies capable of differentiating between two genetically determined molecular variants of normal factor IX. Most patients with severe hemophilia B lacked demonstrable IX:Ag. The factor IX variant that is undetectable with one of the monoclonal antibodies used was present in 2 out of 6 families with moderate haemophilia B and in 1 out of 6 families with mild haemophilia B. The existence of allotypes of factor IX in hemophilia B may have practical implications for carrier detection and prenatal diagnosis.

Studies on immunological assay of vitamin-K dependent factors. III. A double monoclonal immunoradiometric assay for factor IX antigen

Two-site immunoradiometric assays (IRMAs) for factor IX antigen (IX:Ag) were developed using a monoclonal antibody (RFF-IX/1) on the solid-phase and either another monoclonal antibody (RFF-IX/4) or a human polyclonal inhibitor antiserum as tracer (M-M and M-I IRMA respectively). The lower sensitivity limits of these two assays for IX:Ag in normal reference plasma were 4 X 10(-4) (M-M IRMA) and 2 X 10(-4) (M-I IRMA) units/ml. In 20 samples of normal plasma, levels of factor IX coagulation activity (IX:C) and of factor IX antigen measured by both IRMAs were highly correlated. Mean values of approximately 1.0 units/ml were obtained in all three assays. In normal serum, IX:Ag levels were lower with means of 0.84 (M-M IRMA) and 0.83 (M-I IRMA) units/ml. 4/25 patients with haemophilia B were CRM neg., two were CRM + and the remaining 19 patients were CRMr variants. In two of these, IX:Ag was detectable by M-I IRMA whilst IX:C and IX:Ag measured by M-M IRMA were undetectable. In plasma from a fetus subsequently terminated on eugenic grounds, IX:C and IX:Ag by both M-M and M-I IRMA were undetectable. In warfarin-treated plasma (n = 12), the level of IX:C was low (mean 0.39 units/ml). The levels of IX:Ag measured by M-M IRMA (mean of 0.80 units/ml) and by M-I IRMA (0.70 units/ml) showed a discrepancy. M-M IRMA reflects the real amount of IX:Ag in warfarinized plasma because both monoclonal antibodies bind to epitopes distant from the light chain carboxylated region. Western blotting of denatured factor IX demonstrated that RFF-IX/1 binds an epitope that is lost after XIa activation. RFF-IX/4 binds the heavy chain. Antigen measured after activation but without denaturing showed loss of 60% reactivity after XIa activation but no change after RVV activation. These data indicate a binding site for RFF-IX/1 within the activation peptide (residues 146-180).

Polymorphism of normal factor IX detected by mouse monoclonal antibodies

Hemophilia B is an X-chromosomal recessive disease due to deficiency of coagulation factor IX. Three monoclonal antibodies against factor IX were prepared and used to develop immunoradiometric assays (IRMAs) of factor IX antigen (IX-Ag). IX-Ag was measured in 65 normal individuals with one IRMA based on polyclonal anti-IX antibodies and two IRMAs based on three monoclonal anti-IX antibodies. One of the monoclonal antibodies differed in specificity since it neutralized less than 50% of the clotting activity of factor IX (IX-C), whereas the other two monoclonal antibodies neutralized 80-95%. When the former antibody was used as the solid phase in IRMA, two groups of normal individuals were distinguished: group A with measurable IX-Ag, and group B without demonstrable IX-Ag. There were no differences between the groups either in IX-C or in IX-Ag measured with polyclonal antibodies. A subgroup comprising only women could be distinguished in group A, in whom intermediate IX-Ag concentrations were found. Family studies showed the group B variant of normal factor IX to be transmitted according to the pattern of X-linked recessive inheritance. The allelic frequency of group A was 0.66, and that of group B was 0.34.

Heterogeneity of hereditary and acquired factor X deficiencies by combined immunochemical and functional analyses

Limited information is available regarding molecular abnormalities associated with derived factor X deficiencies. In order to assess the types of molecular aberrations that may occur in this group of haemostatic diseases we have analysed plasmas of 33 individuals from 28 kindred exhibiting factor X deficiency. These included those of hereditary type, transiently acquired deficiency as well as factor X deficiency associated with amyloidosis. Plasmas were analysed by one-stage assays for factor X activation by the extrinsic coagulation pathway, intrinsic coagulation pathway and Russell's viper venom. Selected plasmas were analysed in two-stage assays. Normal factor X concentration by specific radioimmunoassay was 6.38 +/- 1.29 micrograms/ml. Factor X associated with factor X deficiency were grouped by their specific activities measured for the three activation pathways and antigen concentration. The results suggest that a broad spectrum of molecular aberrations exist in the factor X deficiency states. The most common group of factor X deficiency was associated with abnormal activation of factor X by all three pathways. Variants of factor X associated with primary amyloidosis and transient acquired deficiency appeared to be abnormal molecules and not just reduced factor X concentration. Hereditary abnormal factor X molecules include the spectrum of potential defective molecules. The relationship of factor X structure to function and the heterogeneity of these defective molecules is discussed.

Characterization of three abnormal factor IX variants (Bm Lake Elsinore, Long Beach, and Los Angeles) of hemophilia-B. Evidence for defects affecting the latent catalytic site

Abnormal factor IX variant proteins were isolated from the plasmas of three unrelated severe hemophilia-B families that had been previously shown to contain functionally impaired molecules immunologically similar to normal factor IX. The families studied were: (1) a patient with markedly prolonged ox brain prothrombin time, designated factor IX Bm Lake Elsinore (IXBmLE); (b) three patients (brothers) with moderately prolonged ox brain prothrombin time, designated factor IX Long Beach (IXLB); and (c) a patient with normal ox brain prothrombin time designated factor IX Los Angeles (IXLA). Each variant molecule comigrates with normal factor IX (IXN) both in the sodium dodecyl sulfate and in the nondenaturing alkaline gel electrophoresis. All three variant proteins are indistinguishable from IXN in their amino acid compositions, isoelectric points, carbohydrate distributions and number of gamma-carboxyglutamic acid residues. Each variant protein undergoes a similar pattern of cleavage by factor XIa/Ca2+ and by factor VIIa/Ca2+/tissue factor, and is activated at a rate similar to that observed for IXN. All of the three variant proteins also react with an anti-IXN monoclonal antibody that interferes with the binding of activated IXN(IXaN) to thrombin-treated factor VIIIC. However, in contrast to IXaN, the cleaved IXBmLE has negligible activity (approximately 0.2%), and cleaved forms of IXLA and IXLB have significantly reduced activity (approximately 5-6%) in binding to antithrombin-III/heparin, and in activating factor VII (plus Ca2+ and phospholipid) or factor X (plus Ca2+ and phospholipid) +/- factor VIII. These data, taken together, strongly indicate that the defect in these three variant proteins resides near or within the latent catalytic site. This results in virtually a complete loss of catalytic activity of the cleaved IXBmLE molecule and approximately 95% loss of catalytic activity of the cleaved IXLA and IXLB molecules.

Incidence, significance, and subtypes of hemophilia BM in a large population of hemophilia B patients

Eleven patients with hemophilia BM were found out of a population of 66 patients with hemophilia B. Factor IX activity in the hemophilia BM varied between less than 1% and 1.6% of normal but factor IX antigen was normal or only slightly reduced in each instance. Thrombotest clotting time was variably prolonged and was not corrected by the addition of normal plasma. Thrombotest mixing experiments and dilution curve studies confirmed the presence of the inhibitor in every patient. There are at least two forms of hemophilia BM, a severe one and a mild one. In the first form, Thrombotest is severely prolonged (90-120 s). In the other, the prolongation is mild or moderate (60-80 s). A positive correlation exists between the antigen-activity difference (delta antigen-activity) and the prolongation of Thrombotest both in the propositi and in obligatory carriers. The criteria for the diagnosis of hemophilia BM are the following: prolonged PTT, prolonged Thrombotest, lack of correction of Thrombotest by the addition of normal plasma while PTT is fully corrected. The lack of correction of Thrombotest in the presence of a full correction of PTT, is the unique clotting feature.

[Clinical studies of familial hereditary factor VII deficiency (author's transl)]

The discovery of a severe factor VII deficiency with increased bleeding tendency resulted in investigations of 22 members of the family. In the propositus and in two of his siblings a severe hypoproconvertinemia was demonstrated, a partial deficiency was found in ten persons. Studies of the family confirmed that this disorder is transmitted by an autosomal gene with intermediate penetrance. The mutated gene produces a severe deficiency in the homozygote and partial deficiency in the heterozygote. The parents of the homozygote patients were consanguineous. Hemorrhagic diathesis was noted only in patients with a severe factor VII deficiency. Causes for the variability of the clinical manifestations are discussed.

New methods in coagulation

Recent advances in the elucidation of the molecular biochemistry of the coagulation proteins have provided the foundation for the development of synthetic substrates. These substrates are oligopeptide with either a chromophore or fluorophore group attached to the C-terminal end. They may be used in the laboratory to assay for a number of the serine proteases involved in either coagulation or fibrinolysis. Also, by suitably modifying the assay system, the various inhibitors can be quantitated. These substrates promise to revolutionize the coagulation laboratory allowing for more precise quantitation of trace enzymes and also improved standardization and precision of coagulation assays. In addition to these substrates, the introduction of a number of immunologic procedures into the diagnostic laboratory have been of major importance in elucidating the heterogeneity of hereditary coagulation defects. By correlating the immunologic assays, coagulation assays and clinical picture, a number of subgroups of hereditary deficiencies have been identified. Also, the immunologic assays have provided a means for identifying the carrier state of hemophilia A and have significantly contributed to the improved diagnosis of von Willebrand's disease. The use of ristocetin cofactor assays, when used in conjunction with the Factor VIII antigens, have enable the laboratory to more accurately diagnose the majority of patients with von Willebrand's disease. Ristocetin cofactor may be assayed utilizing either formalin fixed or washed platelets and recently a snake venom has been introduced to assay for this particular aspect of the Factor VIII complex. Platelet specific proteins (i.e., platelet factor 4 and beta-thromboglobulin) may be assayed utilizing either radioimmunoassays or in the case of platelet factor 4 modified coagulation assays. These proteins provide evidence of in vivo platelet activation and hopefully may, in the future, be correlated with platelet kinetics.

Hemophilia B with associated factor VII deficiency: a distinct variant of hemophilia B with low factor VII activity and normal factor VII antigen

Factor VII activity and cross-reacting material was assayed in fresh and deep frozen non-contacted plasma in 43 patients with Hemophilia B belonging to different kindreds. Factor VII activity was found to be slightly decreased (about of 50% normal) in 12 patients, regardless of the thromboplastin used. In an additional patient (hemophilia BM) factor VII was slightly decreased in 1 : 10 diluted plasma but was normal in further diluted plasma. In the remaining 30 patients factor VII activity was normal. No significant variation was found between fresh and deep frozen plasmas. Factor VII antigen or cross-reacting material was normal.

Immunological heterogeneity of haemophilia B: a multicentre study of 98 kindreds

An electroimmunoassay with a precipitating rabbit anti-human factor IX antiserum and an inhibitor neutralization assay with a non-precipitating homologous antibody were used to measure factor IX antigen (IX:Ag) in 117 patients from 98 kindreds with haemophilia B; and to investigate in a mixed population the incidence of different immunological types of the disease. Although the two assays showed an excellent correlation, the electroimmunoassay was selected for its simplicity as a criterion for classification. 52 kindreds, referred to as haemophilia B-, were characterized by severe deficiency of factor IX coagulant activity (less than 0.01--0.03 u/ml) and unmeasurable IX:Ag (less than 0.12 u/ml): this genetic variant of the disease appears to be related to a complete or marked suppression of factor IX synthesis. In 16 kindreds, a severe or moderately severe IX:C deficiency was associated with normal or increased levels of IX:Ag (haemophilia B+): among them, a subgroup of five kindreds could be identified by the additional abnormality of a prolonged Thrombotest clotting time (haemophilia BM). These patients are likely to be the expression of normal or increased synthesis of a factor IX molecule markedly defective in the site(s) responsible for coagulant activity. Reduced levels of IX:Ag (0.12--0.65 u/ml, characterized the remaining 30 kindreds, presenting with IX:C levels ranging from less than 0.01 to 0.21 mu/ml. In 28 there was a significant excess of IX:Ag over IX:C, suggesting a reduced capacity to synthesize the factor IX molecule accompanied by a variable defect in the coagulant site; the remaining two kindreds, which showed a concomitant reduction of IX:C and IX:Ag, are likely to be examples of a true reduction of factor IX synthesis.

Immunologic studies of factor IX (Christmas factor). II. Immunoradiometric assay of factor IX antigen

A solid-phase two-site immunoradiometric assay has been developed which measures factor IX antigen levels as low as 0.0004 u per ml of plasma. In normal individuals, the factor IX antigen level correlated with the factor IX procoagulant level. In haemophilia B, 14 patients had markedly reduced antigen levels (less than 0.06 u/ml) and five had normal levels (greater than 0.60 u/ml).

Inhibitor-neutralisation assay and electro-immuno assay of human factor IX (Christmas factor)

A rabbit antibody specifically precipitating human factor IX has been used in the assay of factor IX antigen. The results obtained with two different methods (inhibitor-neutralisation assay and electro-immunoassay) have been compared in a group of healthy individuals and in a group of hemophilia B patients and carriers. In general, identical results are obtained with both methods, except in some hemophilia B+ carriers and patients, where the electroimmuno assay gives 1.5-2.0 times higher levels. Results obtained by electroimmuno assay are more accurate and reproducible than those obtained by inhibitor-neutralisation assay, which is of importance for its potential use in carrier detection.

Factor IX antigen by radioimmunoassay. Abnormal factor IX protein in patients on warfarin therapy and with hemophilia B

Factor IX, isolated from normal human plasma, was homogenous by polyacrylamide gel electrophoresis in urea and sodium dodecyl sulfate. On the latter, it migrated as a single polypeptide chain with or without reducing agents and had an apparent mol wt of 62,000. After iodination by chloramine-T, a single peak of 125I was found on gels. Immunoelectrophoresis in agarose with rabbit antifactor IX sera gave a single arc against both isolated and partially purified factor IX preparations. The rabbit antibody was specific as it failed to inhibit the activities of prothrombin or factors VII or X in normal plasma. At an additional 20-fold dilution, factor IX activity was inhibited 50%. In a double-antibody radioimmunoassay, excess rabbit anti-human factor IX precipitated 90-95% of the 125I-human factor IX. Control without specific antibody gave 6-8%. Dilutions of a pool of normal human plasma paralleled dilutions of the isolated preparation and were used for the standard curve. Of 39 plasma samples from normal donors, the mean factor IX antigen level was 93% of that of a separate normal pool. The radioimmunoassay detected the abnormal factor IX produced in patients on warfarin therapy. After Al(OH)3 adsorption of warfarin treated patient's plasma, factor IX antigen, but not activity, was present in the supernate. Samples from 28 patients on warfarin gave a mean factor IX clotting activity of 27% with a mean antigen of 69%. The antigen level from the warfarin group was significantly lower than the antigen level of the normal group (P less than 0.001). The factor IX antigen level was then assessed in 36 patients from 29 pedigrees with hemophilia B. The median antigen level was 17% of normal. The distribution of the antigen level was wide with two patients around 100% of normal; only two had levels below the limits of resolution of the radioimmunoassay as currently performed (less than 2%). Within each of the five pedigrees in which more than one affected member was tested, activity and antigen levels were the same. The degree of neutralization of the antibody's inhibition of normal plasma by patient's plasma was highly correlated. Additional evidence for the detection of abnormal protein was provided by immunodiffusion of plasmas concentrated by lyophilization. Reactions of complete identity occurred between normal, a warfarin treated and a hemophilia B subject's plasmas.

An immunological investigation of hemophilia B with a tentative classification of the disease into five variants

23 patients with hemophilia B have been investigated by means of several immunological methods. 16 patients (69.9%) had no detectable factor XI antigen. Five had a normal factor IX antigen and the electrophoretic mobility of this abnormal factor IX was similar to that of its normal counterpart. One of these five patients had hemophilia Bm, since ox brain thromboplastin clotting time was severely prolonged. The remaining two patients had reduced or decreased factor IX antigen. Several patients showed a slight protongation of ox brain thromboplastin time due to an associated slight factor VII deficiency. On the basis of these results, a tentative classification of hemophilia B into five variants is proposed, namely: hemctor IX antigen; hemophilia Bra, or with reduced factor IX antigen; hemophilia Bm, or with normal factor IX antigen and severely prolonged ox brain thromboplastin; hemophilia B patients is feasible only by means of a battery of tests, namely:factor IX activity assay, factor IX antigen determination, ox brain thromboplastin clotting time, factor VII activity assay.

An immunological investigation of factor VIII associated antigen in combined factor V and factor VIII deficiency

The behavior of factor VIII associated antigen of three patients with combined factor V and factor VIII deficiency has been evaluated in several immunological systems. Factor VIII associated antigen resulted to be normal or higher than normal in all three patients in the radial immunodiffusion and in the electroimmunoassay systems. In the bidimensional electrophoresis system only one factor VIII precipitate was evident and such factor VIII precipitate showed the same electrophoretic mobility as normal factor VIII antigen. These findings firmly establish the fact that the factor VIII defect in congenital combined factor V and factor VIII deficiency is of the hemophilia type.

Decrease of normotest/thrombotest discrepancy in non-contacted coumarin plasma after glass or ellagic acid activation

Activation of coumarin plasmas in glass tubes for 60 min resulted in a clear shortening of Thrombotest clotting times. Normotest clotting times were shortened too but to a much lesser extent. As a consequence the Normotest (NT)/Thrombotest (TT) discrepancy which was quite large at 0 time, became progressively smaller. This phenomenon was observed both in undiluted and 6:10 diluted plasma. After ellagic acid activation a similar phenomenon was noted even though a less pronounced shortening of Thrombotest was noted. These data suggest that Thrombotest is very sensitive to contact phase and to factor VII activation and not to any coumarin-induced inhibitors.

Cross-reacting material in genetic variants of haemophilia B

Cross-reacting factor IX material (CRM) was immunologically detected in the plasma of 38 normal individuals and 21 out of 22 haemophilia B patients using a rabbit antibody to factor IX. The same reacting material was detected in only nine of these patients using a human antibody. These results indicate that the plasma of the majority of haemophilia B patients contains a protein-lacking biological activity but having antigenic determinants in common with normal factor IX.