Prothrombin deficiency is a bleeding disorder that slows the blood clotting process. People with this condition often experience prolonged bleeding following an injury, surgery, or having a tooth pulled. In severe cases of prothrombin deficiency, heavy bleeding occurs after minor trauma or even in the absence of injury (spontaneous bleeding). Women with prothrombin deficiency can have prolonged and sometimes abnormally heavy menstrual bleeding. Serious complications can result from bleeding into the joints, muscles, brain, or other internal organs. Milder forms of prothrombin deficiency do not involve spontaneous bleeding, and the condition may only become apparent following surgery or a serious injury.

When prothrombin deficiency is caused by genetic changes (mutations) to the F2gene, it is inherited in an autosomal recessive manner. This means that both copies of the F2 gene must be changed in order for a person to have symptoms of the disease. We inherit one copy of each gene from our mother and the other one from our father. Men and women with a disease-causing change in only one copy of the F2 gene are known as carriers of prothrombin deficiency (or factor II deficiency). When two carriers have children together, for each child there is a:

• 25% chance that the child will have prothrombin deficiency
• 50% chance that the child will be a carrier of prothrombin deficiency like the parents
• 25% chance that the child will have two working copies of the F2 gene, so the child will not have prothrombin deficiency and will not be a carrier

Carriers of prothrombin (factor II) deficiency typically do not show severe signs and symptoms of the disease, but some may have increased bleeding after surgery.

When prothrombin (factor II) deficiency is acquired, it is not caused by genetic changes in the F2 gene. In these cases, the disease typically does not run in families, unless the underlying cause of the associated disease is also passed from parents to children.