Factor XII deficiency

Factor XII deficiency is a rare disorder in which the body makes too little factor XII, also called Hageman factor, a plasma glycoprotein that takes part in the early steps of the blood clotting cascade and activates factor XI. Despite that role the protein appears not to be essential for clotting in the body, so most people with the condition have no symptoms and no unusual bleeding. It is usually found by accident, when routine blood tests before surgery show an abnormally long activated partial thromboplastin time and a laboratory assay then confirms very low or absent factor XII. The inherited form usually follows autosomal recessive inheritance through changes in the F12 gene on chromosome 5, while an acquired form can accompany nephrotic syndrome, liver disease, sepsis, shock or disseminated intravascular coagulation. Clinically it matters mainly because it has to be told apart from the hemophilias and other bleeding disorders. Older reports linked it to blood clots and to repeated miscarriage, but those links remain unproven. The congenital form needs no treatment, and the acquired form is managed by treating the underlying illness. It was first described in 1955 in a patient named John Hageman.