Emicizumab prophylaxis was associated with a significantly lower rate of bleeding events than no prophylaxis among participants with hemophilia A with inhibitors. (Funded by F. Hoffmann-La Roche and Chugai Pharmaceutical; HAVEN 1 ClinicalTrials.gov number, NCT02622321 .).

Coumarin derivatives such as warfarin represent the therapy of choice for the long-term treatment and prevention of thromboembolic events. Coumarins target blood coagulation by inhibiting the vitamin K epoxide reductase multiprotein complex (VKOR). This complex recycles vitamin K 2,3-epoxide to vitamin K hydroquinone, a cofactor that is essential for the post-translational gamma-carboxylation of several blood coagulation factors. Despite extensive efforts, the components of the VKOR complex have not been identified. The complex has been proposed to be involved in two heritable human diseases: combined deficiency of vitamin-K-dependent clotting factors type 2 (VKCFD2; Online Mendelian Inheritance in Man (OMIM) 607473), and resistance to coumarin-type anticoagulant drugs (warfarin resistance, WR; OMIM 122700). Here we identify, by using linkage information from three species, the gene vitamin K epoxide reductase complex subunit 1 (VKORC1), which encodes a small transmembrane protein of the endoplasmic reticulum. VKORC1 contains missense mutations in both human disorders and in a warfarin-resistant rat strain. Overexpression of wild-type VKORC1, but not VKORC1 carrying the VKCFD2 mutation, leads to a marked increase in VKOR activity, which is sensitive to warfarin inhibition.

Emicizumab prophylaxis administered subcutaneously once weekly or every 2 weeks led to a significantly lower bleeding rate than no prophylaxis among persons with hemophilia A without inhibitors; more than half the participants who received prophylaxis had no treated bleeding events. In an intraindividual comparison, emicizumab therapy led to a significantly lower bleeding rate than previous factor VIII prophylaxis. (Funded by F. Hoffmann-La Roche and Chugai Pharmaceutical; HAVEN 3 ClinicalTrials.gov number, NCT02847637 .).

In a Plenary Paper, Young et al describe impressive favorable outcomes of emicizumab prophylaxis in children with hemophilia A and factor VIII inhibitors, reporting a 99% reduction in annualized bleeding, with 77% of patients having no treated bleeding events.

Anticoagulant compounds, i.e., derivatives of either 4-hydroxycoumarin (e.g., warfarin, bromadiolone) or indane-1,3-dione (e.g., diphacinone, chlorophacinone), have been in worldwide use as rodenticides for Ͼ50 years. These compounds inhibit blood coagulation by repression of the vitamin K reductase reaction (VKOR). Anticoagulant-resistant rodent populations have been reported from many countries and pose a considerable problem for pest control. Resistance is transmitted as an autosomal dominant trait although, until recently, the basic genetic mutation was unknown. Here, we report on the identification of eight different mutations in the VKORC1 gene in resistant laboratory strains of brown rats and house mice and in wild-caught brown rats from various locations in Europe with five of these mutations affecting only two amino acids (Tyr139Cys, Tyr139Ser, Tyr139Phe and Leu128Gln, Leu128Ser). By recombinant expression of VKORC1 constructs in HEK293 cells we demonstrate that mutations at Tyr139 confer resistance to warfarin at variable degrees while the other mutations, in addition, dramatically reduce VKOR activity. Our data strongly argue for at least seven independent mutation events in brown rats and two in mice. They suggest that mutations in VKORC1 are the genetic basis of anticoagulant resistance in wild populations of rodents, although the mutations alone do not explain all aspects of resistance that have been reported. We hypothesize that these mutations, apart from generating structural changes in the VKORC1 protein, may induce compensatory mechanisms to maintain blood clotting. Our findings provide the basis for a DNA-based field monitoring of anticoagulant resistance in rodents.

Key Points• High-dose intensive factor VIII treatment increases the risk for inhibitor development in patients with severe hemophilia A.• In patients with severe hemophilia A, factor VIII prophylaxis decreases inhibitor risk, especially in patients with low-risk F8 mutations.The objective of this study was to examine the association of the intensity of treatment, ranging from high-dose intensive factor VIII (FVIII) treatment to prophylactic treatment, with the inhibitor incidence among previously untreated patients with severe hemophilia A. This cohort study aimed to include consecutive patients with a FVIII activity < 0.01 IU/mL, born between 2000 and 2010, and observed during their first 75 FVIII exposure days. Intensive FVIII treatment of hemorrhages or surgery at the start of treatment was associated with an increased inhibitor risk (adjusted hazard ratio [aHR], 2.0; 95% confidence interval [CI], 1.3-3.0). High-dose FVIII treatment was associated with a higher inhibitor risk than low-dose FVIII treatment (aHR, 2.3; 95% CI, 1.0-4.8). Prophylaxis was only associated with a decreased overall inhibitor incidence after 20 exposure days of FVIII. The association with prophylaxis was more pronounced in patients with low-risk F8 genotypes than in patients with high-risk F8 genotypes (aHR, 0.61, 95% CI, 0.85, 95% CI, respectively). In conclusion, our findings suggest that in previously untreated patients with severe hemophilia A, high-dosed intensive FVIII treatment increases inhibitor risk and prophylactic FVIII treatment decreases inhibitor risk, especially in patients with low-risk F8 mutations. (Blood. 2013;121(20):4046-4055)

Prophylactic application of clotting factor concentrates is the basis of modern treatment of severe hemophilia A. In children, the early start of prophylaxis as primary or secondary prophylaxis has become the gold standard in most countries with adequate resources. In adults, prophylaxis is reasonably continued when started as primary or secondary prophylaxis in childhood to maintain healthy joint function. Initial data support that adult patients with already existing advanced joint arthropathy benefit from tertiary prophylaxis with significantly lowered number of bleeds, almost complete absence of target joints, and less time off from work. Current prophylactic regimens, although very effective, do not completely prevent joint disease in a long-term perspective. Joint arthropathy in primary prophylaxis develops over many years, sometimes over a decade or even longer time periods. The ankle joints are the first and most severely affected joints in those patients and thus may serve in outcome assessment as an indicator of early joint arthropathy when followed by ultrasound or magnetic resonance imaging. Optimized outcome and best use of available resources is expected from individualization of therapy regimens, which comprises the individual’s bleeding pattern, condition of the musculoskeletal system, level of physical activity and the pharmacokinetic profile of the substituted coagulation factor, and most recently includes novel products with extended half-lives.

This systematic review was designed to provide more precise effect estimates of inhibitor development for the various types of F8 gene mutations in patients with severe hemophilia A. The primary outcome was inhibitor development and the secondary outcome was high-titerinhibitor development. A systematic literature search was performed to include cohort studies published in peer-reviewed journals with data on inhibitor incidences in the various F8 gene mutation types and a mutation detection rate of at least 80%.