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Haemophilia A (HA) is an X-linked recessive haemorrhagic disorder caused by a deficiency of coagulation factor VIII. Disease causative mutations are heterogeneous and spread all over the F8 gene sequence, with the exception of intron 22 inversion occurring in about 50% of severe patients. To define the specific mutational repertoire and mutation detection rate, we analysed F8 gene, by polymerase chain reaction and direct sequencing, in 128 unrelated patients from Southern Italy with severe ( n = 108), moderate ( n = 9) or mild ( n = 11) HA. We identified 120 mutations, including 64 cases of intron 22 inversion (53.3%), three of intron 1 inversion (2.5%), one large deletion (0,8%) and 52 point mutations (43.3%). In particular, 19/120 were novel and 7/52 point mutations (13.5%) occurred at CpG sites. We also investigated eight prothrombotic genetic variants in a subgroup of 74 severe HA patients to evaluate their possible protective effect on the severity of clinical expression. Methylenetetrahydrofolate reductase A1298C and plasminogen activator inhibitor-1 4G variants recurred more frequently in HA patients with a less-severe phenotype. Clinical impact of these findings needs large-scale studies to further define the role of these prothrombotic variants as possible modifier factors of HA phenotype. [ABSTRACT FROM AUTHOR]