PROS1 and Rare hereditary thrombophilia: In children with high-risk thrombophilia, the annual recurrence rates were 5.4% (95% CI, 2.6–10%) in children with antithrombin deficiency, but only 1.3% (95% CI, 0.3–3.8%) and 0.7% (95% CI, 0.08–2.4%) in protein C and protein S deficient patients, respectively.