F10 and hyperinsulinemic hypoglycemia, familial, 4: Homozygous deficiency of prothrombinase cofactor FV is rare and is associated with mild to severe hemorrhagic symptoms (45), whereas FX deficiency is one of the most severe rare coagulation defects, causing bleeding symptoms such as hematomas, and umbilical cord, gastrointestinal, and central nervous system bleeding (46).