Family studies of patients with reduced ristocetin aggregation and abnormalities of factor VIII and/or platelet function.

Factor VIII procoagulant activity (VIIIc), antigen (vWa), mobility of the antigen on two dimensional immunoelectrophoresis and platelet function were studied in 9 families with reduced ristocetin induced platelet aggregation rate (RIPA) and/or deficiency of plasma factor(s) required for ristocetin aggregation of washed normal platelets (vWf). the families could be subdivided into 4 groups. Group I showed dominant inheritance and reduced levels of VIIIc and vWa characteristic of typical von Willebrand's disease. All patients had reduced vWf and in 7 of 10 RIPA was reduced. Group II showed normal levels of VIIIc but reduced vWa. All showed reduced vWf but RIPA was reduced in one patient only. There was a good correlation between vWf and vWa and VIIIc in both groups. The bleeding time correlated with vWf in group I but not group II. Group III showed normal or nearly normal VIIIc and vWa but there was an increased mobility of vWa compared to normals and to groups I and II. RIPA was markedly reduced as was the vWf in one patient. Group IV is represented by one child with a strong family history of bleeding, who had reduced RIPA and defective platelet release reaction. The vWf in this child was normal and the ratio between VIIIc and vWa was similar to that seen in carriers of haemophilia. This spectrum of abnormalities of ristocetin aggregation justifies the use of the term 'von Willebrand's syndrome'.

Use of rabbit antisera in the preparation of factor-XII-free platelet-rich and platelet-poor plasma.

Antibodies were raised in rabbits against purified human factor XII and insolubilized on Sepharose. This preparation of insolubilized anti-factor XII antibody was used to prepare factor-XII-free human platelet-rich and plate-poor plasma for use in the study of platelet coagulant activities.

The role of factor XI in the coagulant activity of platelets.

Washed platelets were ruptured by freezing and thawing; a coagulant activity was released which would correct the clotting time of factor XI (FXI)-deficient plasma only in the presence of kaolin. Platelets from a FXI-deficient patient treated in a similar fashion also released a coagulant activity which could be absorbed onto Sepharose-heparin and eluted similarly to plasma FXI. Collagen was employed to induce a coagulant activity in platelet-poor plasma (PPP) and platelet-rich plasma (PRP) in the presence and absence of antibodies developed to purified FXI and FXII. The presence of FXII antibody had little effect on the activity induced in PRP. However, the presence of FXI antibody eliminated the difference between PPP and PRP. An activity was induced when FXI-deficient PRP was incubated with collagen and none with PPP. One type of collagen failed to induce a coagulant activity.

Platelet release abnormality associated with a variant of von Willebrand's disease.

A family with a platelet release abnormality (PRA) is described. The only son also showed a reduced rate of platelet aggregation in response to ristocetin, markedly reduced levels of von Willebrand's factor (vWf, ristocetin cofactor), and increased mobility of factor VIII-like antigen, features which were suggestive of von Willebrand's disease (vWd). No inhibition of vWf was found in his plasma. Family studies showed no evidence of vWd in the mother. The father's investigations showed a low rate of ristocetin aggregation on one of the two occasions when it was tested and low vWf on two of four occasions. Despite repeated testing, the findings in the father did not conclusively rule out the possibility of mild vWd, and it was impossible to determine whether the vWd in the son was inherited or arose as a mutation. The findings in this family suggest a possible relationship between abnormalities of the factor VIII complex and defective platelet function.

Assessment of the value of factor VIII procoagulant and antigen ratio in the diagnosis of carriers of haemophilia.

The detection rate of carriers of haemophilia was evaluated using the ratio of factor VIII procoagulant activity (VIIIc) to factor VIII antigen (VIIIag). In normals the corelation coefficient of VIIIc to VIIIag was 0.82. In 15 obligatory carriers of haemophilia whose VIIIc and VIIIag levels were studied in the authors' labotatory there was no correlation between VIIIc and VIIIag and the ratio of VIIIc to VIIIag was below the lowest normal value in 12 (80%). In all five obligatory carriers whose VIIIc levels were estimated in the referring institution and VIIIag levels in the authors' laborary the ratio was below the lowest normal value. In 17 sisters of haemophiliacs studied here or referred for estimation of VIIIag only, an abnormal ratio was found in seven. Of 25 mothers of haemophilic children without a family history of haemophilia carriers is close to that expected on theoretical grounds but the interpretation of the results is complicated by the small numbers of patients all of whose studies were performed entirely in the authors' laboratory. In two normal individuals, one of who was on a contraceptive pill, there were no fluctuations of the ratio of VIIIc to VIIIag during the menstrual cycle. In one obligatory carrier with a normal ratio there was also no fluctuation. It is concluded here that a measurement of the ratio of VIIIc to VIIIag is a valuable adjuvant in genetic counselling in haemophilia.

Ristocetin in the diagnosis of von willebrand's disease: a comparison of rate and percent of aggregation with levels of the plasma factor(s) necessary for ristocetin aggregation.

Percent aggregation and the aggregation rate of platelet rich plasma (PRP) in response to ristocetin (1.75 mg/ml) were measured in 20 normals and 16 patients with von Willebrand's disease (v Wd), with and without the addition of acetylsalicylic acid (ASA). Percent aggregation did not clearly distinguish between normals and patients with vWd. Aggregation rate was normal in only 2 of 16 patients, and after incubation of PRP with ASA 1 of these 2 remained normal. The corrective effect of dilutions of platelet poor plasma (PPP) on the ristocetin response of washed platelets (von Willebrand's factor, vWf) was measured in 21 normals and 12 patients with vWd. All patients with vWd had abnormal levels. There was a significant correlation between aggregation rate and vWf in patients with vWd but not in normals. Both tests appear to measure closely related defects, and the aggregation rate is as specific as the vWf level for the diagnosis of clinically affected patients.