Case 3: Risk Factors for Inhibitor Development

• Unclear why some patients develop inhibitors

• An inhibitor risk score can be used to distinguish severe hemophilia A patients with a high risk of inhibitors from those with an intermediate or low risk

• The risk score sums the independent weights of three predictors present at initial treatment

• Intensive treatment of 5 or more consecutive days of FVIII (3 points)
• Family history of inhibitors (2 points)
• FVIII gene mutation* type (2 points)

• Higher the score, the greater the risk of developing inhibitors

*Factor VIII gene mutation type was divided into high-risk mutations (large deletions of over 200 base pairs, nonsense mutations, intron 22 or one inversions) and low-risk mutation types (small deletions/insertions of < 200 base pairs, missense mutations, and other mutations including splice site defects or promoter mutations).

Ter Avest PC, et al. J Thromb Haemost. 2008;6:2048-2054.