Here, we challenged the ExSpeU1s in the F8 exon 5 as a model of context in which the authentic 5’ss is surrounded by various cryptic 5’ss (Figure 1A), a scenario further complicated by the occurrence of nucleotide changes at the 5’ss that are associated with coagulation factor VIII (FVIII) deficiency (Haemophilia A, HA) (Bolton-Maggs and Pasi, 2003). This evidence concerns the gene F8 and hemophilia A.