Whole-exome sequencing to identify genetic risk variants underlying inhibitor development in severe hemophilia A patients.

The development of neutralizing antibodies (inhibitors) against coagulation factor VIII (FVIII) is the most problematic and costly complication of FVIII replacement therapy that affects up to 30% of previously untreated patients with severe hemophilia A. The development of inhibitors is a multifactorial complication involving environmental and genetic factors. Among the latter, F8 gene mutations, ethnicity, family history of inhibitors, and polymorphisms affecting genes involved in the immune response have been previously investigated. To identify novel genetic elements underling the risk of inhibitor development in patients with severe hemophilia A, we applied whole-exome sequencing (WES) and data analysis in a selected group of 26 Italian patients with (n = 17) and without (n = 9) inhibitors. WES revealed several rare, damaging variants in immunoregulatory genes as novel candidate mutations. A case-control association analysis using Cochran-Armitage and Fisher's exact statistical tests identified 1364 statistically significant variants. Hierarchical clustering of these genetic variants showed 2 distinct patterns of homozygous variants with a protective or harmful role in inhibitor development. When looking solely at coding variants, a total of 28 nonsynonymous variants were identified and replicated in 53 inhibitor-positive and 174 inhibitor-negative Italian severe hemophilia A patients using a TaqMan genotyping assay. The genotyping results revealed 10 variants showing estimated odds ratios in the same direction as in the discovery phase and confirmed the association of the rs3754689 missense variant (OR 0.58; 95% CI 0.36-0.94; P = .028) in a highly conserved haplotype region surrounding the LCT locus on chromosome 2q21 with inhibitor development.