Target capture next‐generation sequencing in non‐inversion haemophilia: an alternative approach

The spectrum of FVIII gene variants detected by next generation sequencing in 236 Chinese non-inversion hemophilia A pedigrees

INTRODUCTION

The reported variants of hemophilia A are mainly from European subjects and American subjects of European descent, and limited data are available from more diverse ethnic backgrounds. This study was performed to identify the causative variants in a large HA cohort from Chinese population.

MATERIALS AND METHODS

A total of 236 HA pedigrees were included. Molecular analysis of F8 gene was performed using next-generation sequencing (NGS) and then validated by Sanger sequencing and multiplex ligation probe amplification (MLPA) results. Variants were classified as pathogenic, likely pathogenic, variant of unknown significance, likely benign, and benign according to the American College of Medical Genetics and Genomics guidelines.

RESULTS

A total of 186 F8 variants were identified, with 139 (139/186, 74.73%) point mutations, 44 (44/186, 23.66%) small insertions/deletions (InDels), and 3 (3/186, 1.61%) large deletions, they included 80 pathogenic and 84 likely pathogenic variants. Of these variants, 119 had been reported previously, and 67 were novel. No potentially causative mutations were found in the targeted F8 region in seventeen HA pedigrees.

CONCLUSIONS

The spectrum of F8 variants identified in this study provides additional information about HA and enriches our knowledge of the variant spectrum in a wider range of ethnic backgrounds.

Molecular analysis of 76 Chinese hemophilia B pedigrees and the identification of 10 novel mutations

BACKGROUND

Hemophilia B (HB) is an X-linked recessive inherited bleeding disorder caused by mutations in the F9 gene that lead to plasma factor IX deficiency. To identify the causative mutations in HB, a molecular analysis of HB pedigrees in China was performed.

METHODS

Using next-generation sequencing (NGS) and an in-house bioinformatics pipeline, 76 unrelated HB pedigrees were analyzed. The mutations identified were validated by comparison with the results of Sanger sequencing or Multiplex Ligation-dependent Probe Amplification assays. The pathogenicity of the causative mutations was classified following the American College of Medical Genetics and Genomics guidelines.

RESULTS

The mutation detection rate was 94.74% (72/76) using NGS. Of the 76 HB pedigrees analyzed, 59 causative variants were found in 72 pedigrees, with 38 (64.41%) missense mutations, 9 (15.25%) nonsense mutations, 2 (3.39%) splicing mutations, 5 (8.47%) small deletions, 4 (6.78%) large deletions, and 1 intronic mutation (1.69%). Of the 59 different F9 mutations, 10 were novel: c.190T>G, c.199G>T, c.290G>C, c.322T>A, c.350_351insACAATAATTCCTA, c.391+5delG, c.416G>T, c.618_627delAGCTGAAACC, c.863delA, and c.1024_1027delACGA. Of these 10 novel mutations, a mosaic mutation, c.199G>T(p.Glu67Ter), was identified in a sporadic HB pedigree. Using in-silico analysis, these novel variants were predicted to be disease-causing. However, no potentially causative mutations were found in the F9 coding sequences of the four remaining HB pedigrees. In addition, two HB pedigrees carrying additional F8/F9 mutations were discovered.

CONCLUSION

The identification of these mutations enriches the spectrum of F9 mutations and provides further insights into the pathogenesis of HB in the Chinese population.