Prekallikrein deficiency

A condition characterized by the congenital or acquired deficiency of prekallikrein. This deficiency is usually not associated with bleeding. The congenital deficiency is very rare. Acquired deficiency may occur in diffuse intravascular coagulation, infections, and sickle cell disease. Prekallikrein deficiency is a blood condition that usually causes no health problems. In people with this condition, blood tests show a prolonged activated partial thromboplastin time (PTT), a result that is typically associated with bleeding problems; however, bleeding problems generally do not occur in prekallikrein deficiency. The condition is usually discovered when blood tests are done for other reasons.

Epidemiology

The prevalence of prekallikrein deficiency is unknown. Approximately 80 affected individuals in about 30 families have been described in the medical literature. Because prekallikrein deficiency usually does not cause any symptoms, researchers suspect that most people with the condition are never diagnosed.

Cause

Prekallikrein deficiency is caused by mutations in the KLKB1 gene, which provides instructions for making a protein called prekallikrein. This protein, when converted to an active form called plasma kallikrein in the blood, is involved in the early stages of blood clotting. Plasma kallikrein plays a role in a process called the intrinsic coagulation pathway (also called the contact activation pathway). This pathway turns on (activates) proteins that are needed later in the clotting process. Blood clots protect the body after an injury by sealing off damaged blood vessels and preventing further blood loss.

The KLKB1 gene mutations that cause prekallikrein deficiency reduce or eliminate functional plasma kallikrein, which likely impairs the intrinsic coagulation pathway. Researchers suggest that this lack (deficiency) of functional plasma kallikrein protein does not generally cause any symptoms because another process called the extrinsic coagulation pathway (also known as the tissue factor pathway) can compensate for the impaired intrinsic coagulation pathway.

Inheritance

Autosomal recessive inheritance, a 25% chance

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Symptoms

A few people with prekallikrein deficiency have experienced health problems related to blood clotting such as heart attack, stroke, a clot in the deep veins of the arms or legs (deep vein thrombosis), nosebleeds, or excessive bleeding after surgery. However, these are common problems in the general population, and most affected individuals have other risk factors for developing them, so it is unclear whether their occurrence is related to prekallikrein deficiency.

Diagnosis

Diagnosis is based on the presence of a great prolongation of partial thromboplastin time and normal prothrombin time and thrombin time. The long partial thromboplastin time is fully corrected by the addition of normal plasma or normal serum and presents the unusual feature of shortening on long incubation times. Platelet and vascular tests are normal. Immunological studies allow differentiation into two types, namely cases of true deficiency, which are approximately 70% of the total, and cases with abnormal forms. PK is a glycoprotein synthesized in the liver as a single-chain peptide of 88000 Da. It mostly circulates (∼75%) as a complex with high-molecular-weight kininogen. It is cleaved by FXIIa into a heavy chain and a light chain (catalytic domain), held together by disulfide bonds.

NIH genetic and rare disease info

• NIH info on Prekallikrein deficiency

Prekallikrein deficiency is a rare disease.

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