A Novel Molecular Indicator for Inhibitor Development in Haemophilia A

Abstract

Aim: Previous studies have reported inhibitor development (ID) risk in those patients who have hemophilia A (HA) with missense mutations to be 3-10%. We investigated the association between ID risk and various features of missense mutations; including the impact directly related to amino acid group change. Materials and Methods: Missense mutations in the F8 gene, clinical findings of the patients including severity of HA, and ID status were obtained from the F8 gene variant database (http://www.factorviii-db.org/). Twenty amino acids were then classified into groups according to their side chains. All information regarding each specific mutation, as well as any impact of the mutation on the amino acid group change, was recorded. Additionally, localization (at which domain) of any changed amino acid in the F8 protein was noted. Combined Annotation Dependent Depletion (CADD), Rare Exome Variant Ensemble Learner (REVEL), Mendelian Clinically Applicable Pathogenicity and Deleterious Annotation using Neural Networks scores were applied to identify a significant cut-off value indicative of ID. Results: Three variations were identified that could be considered as useful in the prediction of ID in mild HA. The first being that among mild HA patients, 7.9% (n=70/883) with mutations causing no amino acid group changes showed ID. This rate, however, was only 2.9% in patients with mutations leading to amino acid group changes. Secondly; in patients with mutations causing no amino acid group changes affecting A2, A3 and C2 domains, ID risk was found to be higher than in patients with mutations leading to amino acid group changes. Thirdly; an association between ID and CADD and REVEL scores was observed. Conclusion: In mild HA patients, the characteristics of missense mutations in terms of amino acid group changes, and CADD and REVEL scores could be of considerable utility in the prediction of ID risk.