Genetic risk stratification to reduce inhibitor development in the early treatment of hemophilia A: a SIPPET analysis

A recent randomized trial, the Survey of Inhibitors in Plasma-Product Exposed Toddlers (SIPPET), showed a higher risk of inhibitor development with recombinant factor VIII (rFVIII) than plasma-derived concentrates (pdFVIII). We investigated whether risk stratification by F8 mutation identifies patients who do not suffer this deleterious effect of rFVIII. Among 235 randomized patients with severe hemophilia A previously untreated with FVIII concentrate, 197 with null mutations were classified as high risk and 38 with non-null mutations were classified as low risk. With pdFVIII, no inhibitors occurred in those with low genetic risk, whereas high-risk patients had a cumulative incidence of 31%. The risk among low- and high-risk patients did not differ much when they were treated with rFVIII (43% and 47%, respectively). This implies that patients with low genetic risk suffer disproportionate harm when treated with rFVIII (risk increment 43%), as also shown by the number needed to harm with rFVIII, which was 6.3 for genetically high-risk patients and only 2.3 for low-risk patients. Risk stratification by F8 mutation does not identify patients who can be safely treated with rFVIII, as relates to immunogenicity. This trial was registered at the European Clinical Trials Database (EudraCT) as #2009-011186-88 and at www.clinicaltrials.gov as #NCT01064284.