Genetic changes in severe haemophilia A: new contribution to the aetiology of a complex disease.

Haemophilia A is an X-linked bleeding disorder caused by reduced or absent clotting factor VIII (FVIII) activity, determined by heterogeneous mutations in the F8 gene. Identification of these pathogenic mutations is important for genetic counseling and the assessment of clinical manifestations. Although more than 700 mutations of the F8 gene have been reported as responsible for severe haemophilia (FVIII: C<1%), the corresponding data is currently insufficient for southern Brazilian populations, and world reviews concerning these changes are scarce. Thirty-six unrelated severe haemophilia A patients who showed negative results for introns 22 and 1 inversions were studied for gross exon deletions and mutations there and in adjacent regions. Missense mutations were examined using molecular structural methods. The presence of FVIII inhibitors was also investigated. The results were compared with the information available from respectively 2878 and 1952 patients from all over the world. Twenty-nine different genetic changes were found, 16 of them novel. Seventeen of the carriers developed FVIII inhibitors, and molecular analysis suggested that Asp542Gly and Ser109Pro may interfere with calcium binding, whereas Leu2297Arg clearly affects the molecule's electrostatic surface. The main aetiological factor in the severe form of haemophilia seems to be missense mutations. Of all genetic changes occurring in these patients, large deletions are the most important in inhibitors formation.