Factor IX inhibitors in haemophilia B: A report of National Haemophilia Registry in China

INTRODUCTION

The development of inhibitors against factor FIX (FIX) is the most serious complication of FIX replacement therapy in haemophilia B (HB) patients. Currently, only few cohorts of HB inhibitor patients have been reported worldwide.

AIM

This Chinese nationwide study of HB inhibitor patients explored their risk factors for FIX inhibitor development and experience on their management.

METHODS

We retrospectively analysed patient characteristics, F9 genotypes, treatment strategies and outcomes of HB inhibitor patients registered to the Chinese National Registry and Patient Organization Registry.

RESULTS

Forty-four unique HB inhibitor patients were identified in 4485 unique HB patients registered by year 2021 to the two Registries. Inhibitor diagnosis were usually delayed and the low prevalence (.98%) may suggest some inhibitor patients were not identified. Their median age at inhibitor diagnosis was 7.5 (IQR, 3.0-14.8) years. Most patients (95.5%) had high-titre inhibitors. Allergic/Anaphylactic reactions occurred in 59.1% patients. Large deletions and nonsense mutations were the most common F9 mutation types in our FIX inhibitor patients. Patients with large F9 gene deletions were more likely to develop inhibitors (p = .0002), while those with missense mutations had a low risk (p < .0001). Thirteen (29.5%) patients received immune tolerance induction (ITI) therapy using low-dose prothrombin complex concentrate regimens. Twelve completed ITI with three (25.0%) achieving success. Nephrotic syndrome developed in two (16.7%) patients during ITI.

CONCLUSION

This study reports the largest Chinese cohort of HB inhibitor patients. Large deletions were most significantly associated with inhibitor development. Low-dose ITI might be feasible for FIX inhibitor eradication.

Risk factors associated with inhibitor development in Chinese patients with haemophilia B

INTRODUCTION

Inhibitor development is a severe complication of factor IX substitution treatment for haemophilia B (HB). Current research examined the association between inhibitor development and F9 genotypes and polymorphisms in immune response genes in Chinese HB patients.

MATERIALS AND METHODS

11 inhibitor-positive HB patients and 41 inhibitor-negative HB patients were enrolled. Direct sequencing, copy number variation (CNV) detection and fragment length analysis were applied to identify F9 genotypes and 15 polymorphisms in immune response genes.

RESULTS

7 patients developed high titer inhibitors, with 5 of them having histories of consecutive exposure to FIX products on demand for at least 5 days. Allergic reactions/anaphylaxis to prothrombin complex concentrates (PCC) occurred in 3 patients before inhibitors were detected. Five nonsense mutations (E54X, R75X, Q185X, R298X and R379X), two large deletions (E1~6del and E1~8del) and one missense mutation (S411G) were identified in patients with inhibitors. Missense mutations had a low odds ratio for FIX inhibitors development (IOR) of 0.078 (P = 0.02), while nonsense mutation presented a high IOR of 8.500 (P = 0.0044). The frequency of allele T in CD44(95102) (A/T) was significantly higher in inhibitor-negative patients, with OR of 0.324 (P = 0.04).

CONCLUSIONS

Nonsense mutations conferred a higher risk for while allele T in CD44(95102) (A/T) might play a protective role against inhibitor development in Chinese HB patients.