Girolami A, et al. - Researchers examined thrombotic event incidence in patients heterozygous for FXII deficiency over a long period of observation. They followed 103 heterozygotes for FXII deficiency (49 female and 54 male) for 19.6 years (range 5–32 years) and included 103 unaffected family members of same sex and similar age as controls. The mean factor XII level was 48.5% (range: 35%–60%) in the heterozygotes and 96.5% (range 70–155%) in controls. Observations revealed no increased incidence of thrombotic events among heterozygotes for FXII deficiency vs unaffected family members over a long follow up.