Mutational spectrum and deep intronic variants in the factor VIII gene of haemophilia A patients. Identification by next generation sequencing.

Haemophilia A (HA) is caused by a broad spectrum of different mutation types in the factor VIII gene (F8). In our patient cohort of more than 2600 HA patients as well as in other published studies, the most frequent cause are missense mutations in different F8 exons or the recurrent intron 22 inversion. Some exons and several specific nucleotide positions represent hot spots for point mutations in the examined cohort. About 4 % of cases remain without mutation after routine HA diagnostic methods including inversion PCRs, Sanger sequencing and multiplex ligation-dependent probe amplification (MLPA). Deep intronic mutations cannot be detected by current standard HA diagnostics but have been reported for several genetic disorders. However, next generation sequencing (NGS) of the whole genomic sequence of the F8 gene allows to identify deep intronic variants. Conclusion: In general, NGS provides an effective approach to screen for different HA causing mutation types in the F8 gene.