There is a direct correlation between these preferred codons and the relative abundance of corresponding tRNAs.22 However, codon usage bias is species-specific and it is thus somewhat surprising that despite adapting usage to a Homo sapien bias, optimized FVIII transgenes have been associated with supraphysiological levels of FVIII in hemophilia A mice.19,21 Codon-optimization of genes is extensively used in the production of many recombinant therapeutic proteins. This evidence concerns the gene F8 and hemophilia.