Genetic changes in severe haemophilia A: new contribution to the aetiology of a complex disease

Variants p.Pro2063Ser and p.Arg324* co-segregate in type 3 von Willebrand disease patients from Southern Brazil

INTRODUCTION

von Willebrand factor (VWF) is a multimeric plasma glycoprotein that plays an important role in haemostasis. von Willebrand disease (VWD) is an inherited heterogeneous bleeding disorder caused by either a quantitative or qualitative defect of VWF. Type 3 VWD, the most severe form of the disease, leads to complete quantitative VWF deficiency.

AIM

The present study aims to investigate the molecular pathogenesis of type 3 VWD patients from Southern Brazil.

METHODS

The VWF gene was sequenced in 26 cases clinically diagnosed with type 3 VWD by next-generation sequencing using Ion Torrent PGM.

RESULTS

In 25 patients, we were able to identify both disease-causing variants. We identified 72 different variants: 31 intronic and 41 exonic. Five novel variants were found: c.6976+5G>T; c.6885_6886insC; c.3378C>T (p.Cys1126); c.3346_3347insCCA; and c.2503G>T (p.Glu835*). Variants p.Pro2063Ser and p.Arg324* co-segregated in 17 patients, 15 of them in homozygosity.

CONCLUSION

Our results may contribute to the discussion on whether the variant p.Pro2063Ser is pathogenic or not. Finally, the presence of a common haplotype in patients bearing these two variants suggests a founder effect for this variant in our region.

Factor VIII mutations and inhibitor formation in a southern Brazilian population

A total of 110 patients with severe (n = 43), moderate (n = 15) or mild (n = 52) haemophilia A were studied in relation to their F8 gene mutation and inhibitor status. Nineteen percentage of them had anti-factor VIII antibodies. Significant heterogeneity in inhibitor prevalence considering the location of the patients' mutation was found, with higher frequencies in carriers of mutations in the C1 and B domains. Twelve specific mutations showed associations with inhibitor formation, seven deletions, two nonsense, two insertions and one missense changes. Bioinformatic analysis of the missense mutation confirmed the formation of a B-cell epitope in the protein. This information is important for comparative purposes with series of other ethnic constitutions, as well as for individual prevention of this serious clinical problem in the patient population.