ARTERIAL AND VENOUS THROMBOSIS IN 2 ITALIAN FAMILIES WITH THE FACTOR-V ARG(506)-]GLN MUTATION

APC resistance, due to a point mutation in factor V at amino acid posi tion Arg(506), has been identified as a major cause of inherited throm bophilia. Here we report the presence of the factor V Arg(506) --> Gln mutation in 2 Italian families. In 1 family 3 subjects heterozygous a nd 2 subjects homozygous for the factor V Arg(506) --> Gln mutation we re identified. The only subject who developed a thrombotic event was a 20-yr-old girl who was found to be homozygous for the factor V Arg(50 6) --> Gln mutation. In the second family 10 subjects were identified to be heterozygous for the factor V Arg(506) --> Gln mutation; among t hem 2 developed a thrombotic event. In the same family 2 individuals w ere found to be homozygous for the mutation: the first had a myocardia l infarction at age 25 yr and the second suffered from multiple episod es of deep venous thrombosis and had a stroke at age 24 yr. These data show that the risk of developing deep venous thrombosis for the carri ers of the factor V Arg(506) --> Gln mutation is high in the families investigated. Furthermore our data imply that the factor V Arg(506) -- > Gln mutation in its homozygous form may relate to myocardial infarct ion and stroke.