Spectrum of Molecular Defects in 216 Chinese Families With Hemophilia A: Identification of Noninversion Mutation Hot Spots and 42 Novel Mutations

Hemophilia A (HA) is an X-linked bleeding disorder caused by heterogeneous mutations in the factor VIII gene ( F8). Our aim is to identify the causative mutations in a large HA cohort from China. We studied 216 unrelated HA families. Molecular analyses of F8 were performed using a combination of molecular techniques, including polymerase chain reaction, direct sequencing, and multiplex ligation-dependent probe amplification. The deleterious consequences of the unreported missense mutations were evaluated using various bioinformatics approaches. Causative mutations in F8 were identified in 209 families, intron 22 inversion (Inv22) was identified in 89 severe families, and intron 1 inversion (Inv1) was positive in 5 severe families; 95 mutations were detected among 115 noninversion families, of which 42 were novel, including 29 null variations and 13 missense mutations for which causality was demonstrated via bioinformatics. Among the 53 previously reported mutations, more nonsense (5 of 9) and missense (10 of 26) mutation sites were found to occur at Arginine (Arg) sites and multiple small deletions/insertions (5 of 10) located within the poly-A runs of the B domain. The majority of these sequence variants frequently recurred in the database. The odds ratios for the likelihood of developing inhibitors significantly increased in the presence of nonsense mutation. Our F8 defect spectrum was heterogeneous. Small deletions/insertions in the poly-A runs of the B domain and nonsense and missense mutations at Arg sites were identified as mutation hot spots. Nonsense mutation increased the risk of developing inhibitors.