n extremely rare autosomal recessive bleeding disorder characterized by low levels of circulating prothrombin. There are 2 main types: type I deficiency, known as true prothrombin deficiency or 'hypoprothrombinemia,' is defined as plasma levels of prothrombin being less than 10% of normal with a concomitant decrease in activity. Type II deficiency, known as 'dysprothrombinemia,' is characterized by normal or low-normal synthesis of a dysfunctional protein.