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

The importance and evolution of bleeding disorder registries

Registries are excellent sources of data to address questions that are typically not evaluated in randomized clinical trials, including natural history, disease prevalence, treatment approaches and adverse events, and models of care. Global and regional registries can provide data to identify differences in outcomes and in haemophilia care between countries, economic settings, and regions, while facilitating research and data sharing. In this manuscript, we highlight five bleeding disorder registries: Country registries from Australia and China, Paediatric Network on Haemophilia Management (PedNet) data on children who have received emicizumab, data from the European Haemophilia Safety Surveillance (EUHASS) system, and data on women and girls with haemophilia from the World Federation of Haemophilia (WFH) registries. Data from these and other bleeding disorder registries have been and will continue to be used to advance patient care, understand treatment patterns and adverse reactions, and identify areas of increased need and focus.

Pleiotropic effects of different exonic nucleotide changes at the same position contribute to hemophilia B phenotypic variation

BACKGROUND

The disease-causing effects of genetic variations often depend on their location within a gene. Exonic changes generally lead to alterations in protein production, secretion, activity, or clearance. However, owing to the overlap between proteins and splicing codes, missense variants can also affect messenger RNA splicing, thus adding a layer of complexity and influencing disease phenotypes.

OBJECTIVES

To extensively characterize a panel of 13 exonic variants in the F9 gene occurring at 6 different factor IX positions and associated with varying severities of hemophilia B (HB).

METHODS

Computational predictions, splicing analysis, and recombinant factor IX assays were exploited to characterize F9 variants.

RESULTS

We demonstrated that 5 (38%) of 13 selected F9 exonic variants have pleiotropic effects. Although bioinformatic approaches accurately classified effects, extensive experimental assays were required to elucidate and deepen the molecular mechanisms underlying the pleiotropic effects. Importantly, their characterization was instrumental in developing tailored RNA therapeutics based on engineered U7 small nuclear RNA to mask cryptic splice sites and compensatory U1 small nuclear RNA to enhance exon definition.

CONCLUSION

Overall, albeit a multitool bioinformatic approach suggested the molecular effects of multiple HB variants, the deep investigation of molecular mechanisms revealed insights into the HB phenotype-genotype relationship, enabling accurate classification of HB variants. Importantly, knowledge of molecular mechanisms allowed the development of tailored RNA therapeutics, which can also be translated to other genetic diseases.