Spectrum and origin of mutations in sporadic cases of haemophilia A in China

Introduction About 30% of haemophilia A ( HA ) patients are sporadic cases. It is important to confirm the mutation origin and carrier status in these families. Aim To describe the spectrum and origin of the mutations in 393 Chinese sporadic HA families and identify potential mosaics among non‐carrier mothers. Methods AccuCopy quantification combined with long‐distance PCR was used for genotyping intron 22/1 inversion (Inv22/Inv1) and Inv22 mosaicism. F8 gene sequences were analysed by direct sequencing. Copy number variations of F8 gene were detected by AccuCopy method. Six short tandem repeats related to F8 gene were applied for linkage analysis. Mosaicism of point mutations/small deletions/insertions was determined by ddNTP primer extension method. Results Most of sporadic patients’ mothers are carriers, in 257 cases with integral family members, 60% have the mutations tracing back to their fathers, 12% to their mothers. 28% had de novo mutations with non‐carrier mothers as revealed by routine genetic studies. Mutation spectrum of sporadic families was different in groups with different origins of mutations. Point mutation (51%) was the predominant mutation type in pedigrees with de novo mutations. While, in families with mutations inherited from maternal grandfathers, Inv22 was the main type (51%). We found somatic mosaic in mothers of 30% (3/10) pedigrees with de novo Inv22 and 11.5% (3/26) pedigrees with point mutations. Conclusion The spectrum of F8 genetic variants identified in sporadic families was fairly diverse. The high prevalence of chimaeras in carriers suggests that more cautions should be taken in genetic counselling of sporadic haemophilia families.