Severe and uncontrollable

bleeding contributes to an increased morbidity and mortality among patients with MHA and inhibitors. Inhibitors are frequently provoked by intensive treatment with therapeutic FVIII concentrates for surgery or trauma [8-11]. A cohort study of 41 patients with MHA that received perioperative FVIII replacement reported a 186-fold (95% CI 25–1403) increased risk of inhibitor development for surgery as the reason for first intensive exposure [11]. This extremely high risk arose by the extreme contrasts in the analysis: the time period of 3 months post surgery was compared to all other periods of 3 months during the study. As patients with MHA need therapeutic FVIII concentrates infrequently and months may pass without any exposure to FVIII concentrate, this comparison overestimates the risk that is inflated tremendously. Time post surgery Vismodegib was compared to time periods without any exposure to FVIII concentrates at all! This teaches us Selleck ICG-001 that the analysis of clinical risk factors in MHA inhibitor development requires a thoughtful methodological approach. Efforts should be made to compare patient groups that have similar baseline likelihood to develop inhibitors and only differ in the single factor that is under investigation (e.g. FVIII treatment for surgery vs. FVIII treatment for other reasons). Especially the number of previous EDs in both groups should

be as similar as possible. The inhibitor

risk of continuous infusion has been the subject of intense debate, as inhibitors were frequently observed following intensive treatment administered by continuous infusion [10, 11]. Other studies could not confirm this association [9, 12]. A large cohort study analysing 1079 continuous infusions in 742 patients with haemophilia A (severe, moderate or mild) established that the absolute inhibitor risk was limited as only nine patients (1.2%) developed an inhibitor [58]. There are over 500 reported causative missense mutations for MHA reported in the Haemophilia MCE A database (http://hadb.org.uk/). In patients with missense mutations the presence of circulating endogenous FVIII protein maintains a state of immunological tolerance towards FVIII. Nevertheless, there are certain missense mutations that predispose to inhibitor development in MHA [7, 59, 60] that are clustered in the A2 domain and the C1–C2 domains, e.g. Arg593Cys, Asn618Ser, Asp274Gly, Arg2150His, Arg2159Cys, Trp2229Cys. These missense mutations may contribute to T-cell epitopes that can bind to common HLA-II types. Furthermore, it appears that a class switch in the amino acid substitution (from small/hydrophobic, neutral, acidic or basic to any other of these classes) increases the inhibitor risk, as was recently established in a study of 720 patients with haemophilia and missense mutations [61].