Glomerular dysfunction leads to significant urinary loss of key antithrombotic proteins, such as antithrombin III and protein S, combined with increased hepatic synthesis of prothrombotic factors.6However, routine coagulation study results and thrombophilia testing in our infant were within the normal neonatal ranges and could not explain the extensive thrombosis observed, which progressed dramatically just over 5 days. Here, PROS1 is linked to Rare hereditary thrombophilia.