[Hereditary deficiency of factor XI in a Portuguese family, the propositus of which had Behçet's disease (author's transl)].

The finding of a hereditary deficiency of factor XI in a Portuguese family confirms that this abnormality is not confined to Ashkenazi Jews. Its transmission is autosomal, recessive and of variable expression, and in this particular family it appeared to be asymptomatic. When infused post-operatively in fresh frozen plasma, Factor XI has a half-life of about 24 hours and a recovery rate of almost 100%. The propositus, a 57-year-old woman, appears to have been "protected" by a homozygous deficiency of Factor XI against the thromboembolic complications of a Behçets disease which had been present for 30 years. Plasma exchange and perfusions of fresh frozen plasma were probably responsible for the regression observed in the symptoms (particularly ocular symptoms) of the disease, then in active phase.