Bleeding propensities in HA patients are inversely correlated with their baseline (i.e., untreated) FVIII:C levels and are classified as mild (5%£FVIII:C<40%), moderate (1%£FVIII:C<5%), or severe (FVIII:C<1%).1,2 Because recurrent hemarthrosis causes crippling joint disease, prophylactic infusions with plasma-derived (pd)-or recombinant (r)-therapeutic-FVIII-proteins (tFVIIIs)—called “products” herein—begin for severe HA patients when toddlers. This evidence concerns the gene F8 and hemarthrosis.