A factor VIII inhibitor in a mild hemophiliac

Impact of Choice of Treatment for Bleeding Episodes on Inhibitor Outcome in Patients With Mild/Moderate Hemophilia A and Inhibitors

Patients with mild/moderate hemophilia A (MHA) may develop inhibitors to factor VIII (FVIII). In this condition, FVIII clotting activity (FVIII:C) baseline levels may remain stable for some patients, but may be reduced to less than 0.01 U/mL for others. Several risk factors for the development of inhibitors in MHA have been proposed. Genetic factors, such as mutations in the FVIII gene, may play a central role; however, other influences, such as intensive treatment with FVIII products, may also be important. Optimal treatment regimens have yet to be determined, not only for the eradication of inhibitors, but also for the management or surgical prophylaxis of hemorrhages associated with this condition. Several treatment options for the control of bleeding in patients with MHA and inhibitors (MHAI) are currently available, and the choice of therapeutic strategy should be given careful consideration; some treatments may produce an anamnestic response, thus delaying the return to FVIII:C baseline levels and adversely affecting the duration of the severe bleeding phenotype. To increase our knowledge of MHAI, a retrospective collection of data is currently being performed among hemophilia centers in France and Belgium. Based on five examples of patients with MHAI collated from preliminary study data, we illustrate the impact on inhibitor outcome of the therapeutic choices used to treat bleeding episodes in these patients.

Intensive exposure to factor VIII is a risk factor for inhibitor development in mild hemophilia A

BACKGROUND

Inhibitors are rare in boys with mild hemophilia A (MHA; factor (F)VIII:C > 5%) but may arise following intense FVIII exposure, e.g. continuous infusion (CI).

OBJECTIVES

To determine the impact of intense FVIII exposure in inhibitor formation in MHA at our institution and to compare this with previous reports.

PATIENTS AND METHODS

We reviewed FVIII exposure and inhibitor development in boys (ages 0-18 years) with MHA followed at our institution from 1996 to 2001 and conducted a Medline search (1966-2002) on the experience of inhibitor development following intensive/CI exposure to FVIII.

RESULTS

We identified 54 boys with MHA. Twenty-nine (54%) had been exposed to FVIII. Seven had received FVIII by CI. Four developed inhibitors; three high titer (at ages 10 years, 16 years and 17 years) and one low titer (at 1 month old). All four had received a CI of recombinant (r) FVIII of at least 6 days within 6 weeks of developing inhibitors. Baseline FVIII levels fell to < 1% in all cases and the three with high-titer inhibitors developed severe bleeding. Immune tolerance therapy (ITT) was attempted in two boys and was successful in one. Our literature search identified 35 cases (only four children) with MHA developing inhibitors following intense FVIII exposure often in the context of surgery.

CONCLUSIONS

The incidence of inhibitors in our MHA population was 7.4%. If expressed according to exposure the incidence was significantly higher: 14% (4/29) for any exposure to FVIII and 57% (4/7) for exposure by CI. A prospective study to address whether CI is associated with an increased incidence of inhibitor development in MHA is warranted.

Successful treatment of high titer inhibitors in mild hemophilia A with avoidance of factor VIII and immunosuppressive therapy

We describe two patients with mild hemophilia A (MHA) who developed high titer inhibitor (HTI) following intensive recombinant factor VIII (rFVIII) concentrate replacement for surgery and trauma. Intranasal desmopressin was instituted shortly following immunosuppressive therapy (IST) and activated prothrombin complex concentrate (APCC) in one case, and following APCC alone in the second case. Avoidance of factor VIII (FVIII) coupled with intranasal desmopressin prophylaxis three times a week resulted in undetectable inhibitor levels. Both patients have had no further bleeding episodes and have been maintained on desmopressin prophylaxis prior to activity for the past 2 to 3 years. Recombinant factor VIIa (rFVIIa) was used successfully prior to a second surgery in one patient without complication.

High-titre factor VIII inhibitor in two children with mild haemophilia A

A frequently encountered complication of therapy given to patients with severe haemophilia A is the development of antibodies to infused factor VIII. While much less common, inhibitors also occur in patients with mild or moderate severity haemophilia A. Often thought to be of low titre and transient, several cases of high-titre inhibitors have been described in patients with mild or moderate haemophilia A. Generally these occur in adults or adolescents following significant infused factor VIII exposure. A review of reported cases revealed only two cases of high-titre inhibitor formation in mild haemophilia A patients younger than 10 years of age. We wish to report our experience with an additional two children with mild haemophilia A and high titre inhibitors, and offer suggestions for the management of these children.

Factor VIII inhibitors in mild and moderate-severity haemophilia A

Inhibitors are an uncommon complication of mild haemophilia, occurring in 3-13% of patients and usually arising during adulthood. The risk of inhibitor development in this group appears to be associated with relatively few high-risk factor VIII genotypes clustered in the A2 and C2 domains, especially the Arg593-Cys and the Trp2229-Cys mutations. Kindreds with these mutations have an inhibitor incidence of up to 40%. These mutations may induce a stable conformational change in the factor VIII molecule rendering it antigenically distinct from wild-type factor VIII. Inhibitors in mild haemophilia usually cross-react with endogenous factor VIII reducing the basal VIIIC to < 0.01 IU/ml, and causing spontaneous bleeding. This bleeding is sometimes severe and life-threatening, two-thirds of patients developing a pattern of soft tissue, gastrointestinal (GI) and urinogenital bleeding reminiscent of acquired haemophilia. Bleeding has been treated with human and porcine factor VIII, bypass therapy and DDAVP. Recombinant factor VIIa and DDAVP have the advantage that they do not induce an anamnestic rise in inhibitor titre. About 60% of these inhibitors disappear in the remainder over a median of 9 months. Few of these inhibitors recur, suggesting that most such patients have become tolerant. The inhibitors persist long-term and remain troublesome in about 40% of patients. The limited data available on immune tolerance induction in this group indicate a generally poor response to this approach. Two of nine achieved tolerance, with a partial response in a further four. Inhibitors are an uncommon but life-threatening complication of haemophilia. This complication should be considered when selecting the treatment modality for patients with a family history of inhibitors, and DDAVP used whenever possible.

The Missense Mutation Arg593 → Cys Is Related to Antibody Formation in a Patient With Mild Hemophilia A

The development of inhibitory antibodies to factor VIII in patients affected by a mild form of hemophilia A (factor VIII < 0.05 IU/mL) is considered a rare event. In this study, we evaluated the relationship between genotype and anti-factor VIII antibody formation in a patient with mild hemophilia A. Mutation analysis showed that a missense mutation in the factor VIII gene leading to replacement of Arg593 by Cys in the A2 domain of factor VIII was associated with hemophilia A in this patient. The anti-factor VIII antibodies present in the patient's plasma were characterized using metabolically labeled factor VIII fragments expressed in insect cells. The anti-factor VIII antibodies, composed of subclasses IgG2 and IgG4, reacted with both the fragment corresponding to the factor VIII heavy chain and the A2 domain. The Arg593 → Cys substitution was introduced into the cDNA encoding the A2 domain of factor VIII and the resulting construct was expressed in insect cells. Strikingly, the metabolically labeled A2 domain carrying the Arg593 → Cys mutation was not recognized by the anti-factor VIII antibodies present in the plasma of the patient. These data indicate that the anti-factor VIII antibodies are exclusively directed against exogenous factor VIII. This strongly suggests that the Arg593 → Cys substitution results in recognition of wild-type factor VIII as nonself and is thereby related to the formation of anti-factor VIII antibodies after factor VIII replacement therapy in this particular patient.

Factor VIII antibody in a patient with mild haemophilia

We present the rare occurrence of an inhibitor of factor VIII procoagulant arising in a patient with mild haemophilia A and rheumatoid arthritis. The inhibitor was transient and behaved like a low titre, type II factor VIII procoagulant inhibitor similar to previously reported cases (Biggs et al, 1972b). In vitro studies confirmed the type II-like interaction of this inhibitor with the factor VIII procoagulant molecule. Factor VIII procoagulant antigen level was equal to the factor VIII procoagulant activity, which excluded dysproteinaemia as the cause. This patient's HLA type has no known association with abnormal immune responsiveness or autoimmune disease, and his clinical course as well as in vitro studies were similar to the eight previously reported cases of factor VIII procoagulant inhibitors arising in mild haemophilia A.