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 Southern blotting and chemical mismatch analysis (CMA) to identify the mutations causing haemophilia A in 59 local or referred patients or carriers of haemophilia A. Southern blot analysis of 87 families with FVIII : C < 5% identified 31 as positive for the intron 22 inversion. Analysis of 19 of the inversion-negative families and a further nine families with mild or moderate haemophilia A by CMA resulted in the identification of a heterogeneous spectrum of mutations in the FVIII gene comprising 21 single base-pair substitutions and nine deletions. Seventeen of the base-pair substitutions are missense, 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 found to be associated with exon-skipping events.