The Analysis of the FIX‐inhibitor Risks Associated With the F9 Genotype in Patients With Haemophilia B Exposes the Involvement of Nonsense Mediated‐decay: Argentinean and International Series

INTRODUCTION: Haemophilia B (HB) associates with deleterious variants in F9. HB management with FIX-concentrate infusions may be ineffective in 3%-9% patients who develop FIX-inhibitors. AIM: To present our HB-series (n = 136) including all Argentinean patients with FIX-inhibitors (n = 13). To estimate F9-genotype-associated FIX-inhibitor risks from our series (GMH), and HB-international databases, FIX-UCL and EAHAD. METHODS: F9-genotyping was performed by conventional protocols; or by short-read-NGS on a new F9-panel. FIX-inhibitor risks were estimated by case(inh+)/control(inh-) studies using OR(95%CI). RESULTS: The spectrum of F9-genotypes from our GMH-series resulted similar to the one compiled in international databases, prevailing missense (45%), and nonsense (21%) in severe-HB and missense defects (> 80%) in non-severe-HB. Our set of HB-patients with FIX-inhibitors mostly included large-deletions and nonsense mutations, and 38.5% developed allergic reactions. Case/Control studies mainly aligned FIX-inhibitor risks in all three datasets. Considering severe-HB in GMH(n = 91)//FIX-UCL(n = 349)//EAHAD(n = 590), we observed a high-risk group that comprised entire-F9-deletions with highly-significant ORs of 24//12//35, all-large-deletions, 7//7//17 and nonsense mutations, 3//3//2; and a low-risk group confined to missense F9-variants with highly-significant protective ORs, 0.04//0.11//0.03, whilst other F9-variants did not differ from the null-hypothesis. Equal analysis from all-severities HB patients closely agreed with these results. An analysis of NS and FIX-inhibitor risks suggested the involvement of nonsense-mediated decay (NMD) in F9: nonsense (F9-exons_1-7) vs nonsense (F9-exon_8) resulted in highly-significantly incremented risks in both FIX-UCL(n = 124)//EAHAD(n = 171), ORs of 4(2-9)//4(3-6). CONCLUSION: Our study provides robust estimations of F9-genotype-associated FIX-inhibitor risks in HB-patients and exposed the involvement of NMD.