The binding was only partially possible to inhibit with the addition of each molecule, however, and was therefore considered primarily unspecific. Thirteen patients with a current negative Bethesda titre had a previous selleckchem history of inhibitors, but no exposure to ITI-therapy (see Fig. 1). Six (46.2%) of these subjects had experienced high-responding

inhibitors with a mean peak titre of 15.6 BU mL−1 (range: 5.0–37.5 BU mL−1, median: 11.5 BU mL−1), whereas the others were low-responders. In two of the plasma samples of the latter subjects, an antibody response was detected in the ELISA assay, whereas this was not the case for the others. The median age did not differ significantly (P = 0.29) in patients without (median: 13.5 years, mean: 15.7 years, range: 1–68 years) and with (median: 14.0 years, mean: 23.2 years, range: 0–74 years) Bethesda-negative selleck kinase inhibitor ELISA-positive antibodies. However, within the subgroup without a history of inhibitory antibodies (n = 122), there was a significant difference in median age of patients with NNA (median: 30.0 years, mean: 28.0 years, range: 1–65 years) compared with patients without NNA (median: 14.0 years, mean: 17.0 years, range: 0–74 years) (P = 0.021). This was not the case in the subgroup with a history of inhibitors (n = 79) (P = 0.43). No significant difference in NNA prevalence was

found, in either the total cohort (n = 201) or any of the two subgroups (with and without history of inhibitors, see Fig. 1), when comparing patients carrying a high-risk mutation, defined as inversions, nonsense mutations or large deletions, with those selleck chemical with a low-risk mutation. Likewise, there was no correlation between race

and NNA development in any cohort analysed (data not shown). As noted above, 53 (67.9%) families had been previously characterized as discordant with respect to an inhibitory antibody response, 8 (10.3%) families concordant with a positive inhibitor titre found in all siblings and 17 families (21.8%) concordant without a history of inhibitors. However, when considering the total FVIII antibody response, the number of discordant families was reduced to 47 (60.3%) and the number of families with an antibody response in all siblings increased to 20 (25.6%), as 10 of the discordant and two of the concordant negative (i.e. no previous antibody response) families showed a FVIII antibody response in all subjects. For example, in one family with three siblings carrying a small deletion mutation, only one had a history of inhibitory FVIII antibodies, but with inclusion of results from the ELISA assays, all three brothers showed an antigenic response towards FVIII (data not shown). In four of the 17 families without a previous inhibitor, at least one sibling had a positive antibody response. In our cohort of 201 patients with severe haemophilia A, the prevalence of NNA (i.e.