The Multifactorial Etiology of Inhibitor Development in Hemophilia: Genetics and Environment

• Immune responses to FVIII sequence variants encoded by ns-SNPs do not contribute appreciably to inhibitor development in African Americans.• African American HA subjects with an intron-22 inversion had a 2-to 3-times-higher inhibitor incidence than whites with the same mutation.African American hemophilia A (HA) patients experience a higher incidence of neutralizing anti-factor VIII (FVIII) antibodies ("inhibitors") vis-à-vis white patients. Nonsynonymous single-nucleotide polymorphisms (ns-SNPs) in the F8 gene encoding FVIII-H484, FVIII-E1241, and FVIII-V2238 are more prevalent in African Americans. This study tested the hypothesis that immune responses to these sites provoke inhibitors. Blood samples were obtained from 174 African American and 198 white HA subjects and their F8 gene sequences determined. Major histocompatibility complex class II binding and T-cell recognition of polymorphic sequences were evaluated using quantitative binding assays and HLA-DRB1 tetramers. Peptides corresponding to 4 common ns-SNPs showed limited binding to 11 HLA-DRB1 proteins. CD4 T cells from 22 subjects treated with FVIII products having sequences at residues FVIII-484, 1241, and 2238 differing from those of putative proteins encoded by their F8 genes did not show high-avidity tetramer binding, whereas positive-control staining of tetanus-specific CD4 T cells was routinely successful. African Americans with an intron-22 inversion mutation showed a 2-3 times-higher inhibitor incidence than whites with the same mutation (odds ratio 5 2.3 [1.1-5.0, P 5 .04]), but this did not correlate with any of the ns-SNPs. We conclude that immune responses to "sequence-mismatched" FVIII products are unlikely to contribute appreciably to the inhibitor incidence in African Americans. (Blood. 2015;126(7):895-904)

Section: Discussionmentioning

confidence: 99%

Factor VIII gene variants and inhibitor risk in African American hemophilia A patients

Gunasekera

Ettinger

Fletcher

et al. 2015

“…[6][7][8] Studies on genetic determinants of inhibitor development have indicated numerous genetic markers, such as the type of causative F8 gene mutation, single nucleotide polymorphisms (SNPs) in the HLA locus and in other immunoregulatory genes, ethnic background, and family history of inhibitors, to be involved in the etiology of this treatment complication.…”

Section: Introductionmentioning

confidence: 99%

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

Gorski

Blighe

Lotta

et al. 2016

Key Points• Exome sequencing of severe hemophilia A patients with/ without inhibitors identified rare, damaging variants in immunoregulatory genes.• Replication confirmed the association of rs3754689 in a conserved haplotype region surrounding the LCT locus with inhibitor development.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 5 17) and without (n 5 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 5 .028) in a highly conserved haplotype region surrounding the LCT locus on chromosome 2q21 with inhibitor development. (Blood. 2016;127(23):2924-2933

“…Risk factors for early inhibitor development include a family history of inhibitors, nonwhite ethnicity, factor VIII mutation, and intense factor VIII replacement therapy. [1][2][3] It is usually assumed that most factor VIII inhibitors arise after relatively few factor VIII exposure days, early in the patient's life, and that the risk of inhibitor development is subsequently very low. [4][5][6] Reports to the United Kingdom National Hemophilia Database (NHD) suggest that new inhibitors may present throughout life in patients with severe hemophilia and that this risk increases in older patients.…”

Section: Introductionmentioning

confidence: 99%

Incidence of factor VIII inhibitors throughout life in severe hemophilia A in the United Kingdom

Hay

Palmer²,

Chalmers

et al. 2011

159

The age-adjusted incidence of new factor VIII inhibitors was analyzed in all United Kingdom patients with severe hemophilia A between 1990 and 2009. Three hundred fifteen new inhibitors were reported to the National Hemophilia Database in 2528 patients with severe hemophilia who were followed up for a median (interquartile range) of 12 (4-19) years. One hundred sixty (51%) of these arose in patients > 5 years of age after a median (interquartile range) of 6 (4-11) years' follow-up. The incidence of new inhibitors was 64.29 per 1000 treatment-years in patients < 5 years of age and 5.31 per 1000 treatment-years at age 10-49 years, rising significantly (P ‫؍‬ .01) to 10.49 per 1000 treatmentyears in patients more than 60 years of age. Factor VIII inhibitors arise in patients with hemophilia A throughout life with a bimodal risk, being greatest in early childhood and in old age. HIV was associated with significantly fewer new inhibitors. The inhibitor incidence rate ratio in HIVseropositive patients was 0.32 times that observed in HIV-seronegative patients (P < .001). Further study is required to explore the natural history of later-onset factor VIII inhibitors and to investigate other potential risk factors for inhibitor development in previously treated patients. (Blood. 2011;117(23):6367-6370)