Site and type of mutations in the factor VIII gene in patients and carriers of haemophilia A

Haemophilia A is an X-linked bleeding disorder caused by reduced or absent FVIII (FVIII) protein caused by mutations in the FVIII gene. We have used S outhern blotting and chemical mismatch analysis (CMA) to identify the mutat ions causing haemophilia A in 59 local or referred patients or carriers of haemophilia A. Southern blot analysis of 87 families with FWIII: C < 5% ide ntified 31 as positive for the intron 22 inversion. Analysis of 19 of the i nversion-negative families and a further nine families with mild or moderat e haemophilia A by CMA resulted in the identification of a heterogeneous sp ectrum of mutations in the FVIII gene comprising 21 single base-pair substi tutions and nine deletions. Seventeen of the base-pair substitutions are mi ssense, two nonsense, and two are splice-site mutations. Two patients were found to have compound mutations with two mutations identified on a single X chromosome. Six of the point mutations and six of the deletions have not been reported previously in the haemophilia A mutation database. Unusually, a missense mutation, as well as deletion and splice-site mutations, was fo und to be associated with exon-skipping events.