Pseudocholinesterase deficiency


Pseudocholinesterase deficiency

Description, Causes and Risk Factors:

Pseudocholinesterase deficiency is a condition in which a person's body is abnormally slow at breaking down a certain class of drugs used for surgical anesthesia. Known as choline esters, the most commonly used of these drugs is called succinylcholine (suxamethonium). This drug is used by doctors to induce muscle relaxation and temporary paralysis, often for the purpose of inserting a breathing tube. After receiving a normal dose of succinylcholine, people with pseudocholinesterase deficiency will experience a longer than normal period of breathing paralysis. Typically medical teams who administer these drugs would be equipped to handle such an event.

People who are carriers of pseudocholinesterase deficiency - that is, people who have one copy of the gene with a mutation and one normal copy - show a slightly prolonged period of breathing paralysis after receiving choline ester drugs. This period lasts longer than 5 minutes but less than an hour. For people with two mutated copies of the gene, this episode lasts more than an hour and can last as long as three hours.

Pseudocholinesterase deficiency can be caused by mutations in the BCHE gene. This gene provides instructions for making the pseudocholinesterase enzyme, also known as butyrylcholinesterase, which is produced by the liver and circulates in the blood. The pseudocholinesterase enzyme is involved in the breakdown of choline ester drugs. It is likely that the enzyme has other functions in the body, but these functions are not well understood. Studies suggest that the enzyme may be involved in the transmission of nerve signals.

Some BCHE gene mutations that cause pseudocholinesterase deficiency result in an abnormal pseudocholinesterase enzyme that does not function properly. Other mutations prevent the production of the pseudocholinesterase enzyme. A lack of functional pseudocholinesterase enzyme impairs the body's ability to break down choline ester drugs efficiently, leading to abnormally prolonged drug effects.

Pseudocholinesterase deficiency can also have non-genetic causes. In these cases, the condition is called acquired pseudocholinesterase deficiency; it is not inherited and cannot be passed to the next generation. Activity of the pseudocholinesterase enzyme can be impaired by kidney or liver disease, malnutrition, major burns, cancer, or certain drugs.

Acquired causes of pseudocholinesterase deficiency include the following:

People, such as neonates, elderly individuals, and pregnant women, with certain physiologic conditions may have lower plasma pseudocholinesterase activity. Pathologic conditions that may lower plasma pseudocholinesterase activity include the following:

    Chronic infections (tuberculosis).

  • Extensive burn injuries.

  • Liver disease.

  • Malignancy.

  • Malnutrition.

  • Organophosphate pesticide poisoning.

  • Uremia.

Less than 1 in 1000 people have pseudocholinesterase deficiency. It is more common among the some Alaskan Eskimos, where it may affect as many as 10%. In the Persian Jewish community, 1 in 10 individuals is a carrier of the mutation screened by Counsyl. Among white Americans, the mutation screened by Counsyl is thought to affect 1 in 3,000.

Symptoms:

Individuals with pseudocholinesterase deficiency have a shortage or absence of the enzyme pseudocholinesterase in their blood serum. If the drug succinylcholine (or another anesthetic derivative of choline) is given during surgery, the respiratory muscles become paralyzed and the patient stops breathing (apnea). Artificial respiration (mechanical ventilation) may be necessary until the drug is eliminated from the body and the affected individual is able to resume breathing. If the person with pseudocholinesterase deficiency is not exposed to a choline-derived anesthetic, he or she may never be aware of having a deficiency of the enzyme pseudocholinesterase.

Diagnosis:

Although the diagnosis is suspected after an episode of prolonged respiratory paralysis following administration of succinylcholine, the diagnosis of pseudocholinesterase deficiency is confirmed by a laboratory test.Serum cholinesterase is a test for the enzymes acetylcholinesterase (also known as RBC cholinesterase) and pseudocholinesterase (also known as butyrylcholinesterase or plasma cholinesterase), which act to break down acetylcholine, a chemical critical in the transmission of nerve impulses. This test may be performed prior to anesthesia with succinylcholine (a paralyzing agent that is eliminated by these enzymes) to exclude a genetic deficiency of these enzymes. This is often done in individuals who have a family history of a prolonged drug effect during anesthesia.

A simplified screening test of pseudocholinesterase enzyme activity can be performed using the acholest test paper. When a drop of the patient's plasma is applied to the substrate-impregnated test paper, a colorimetric reaction occurs. The time it takes the exposed acholest test paper to turn from green to yellow is inversely proportional to the pseudocholinesterase enzyme activity in the plasma sample.

Treatment:

Pseudocholinesterase deficiency is a clinically silent condition in individuals who are not exposed to exogenous sources of choline esters.

Patients with prolonged paralysis following administration of succinylcholine can be treated in the following ways:

    Prophylactic transfusion of fresh frozen plasma can augment the patient's endogenous plasma pseudocholinesterase activity. This practice is not recommended because of the risk of iatrogenic viral infectious complications. However, perioperative transfusion of fresh frozen plasma administered to correct a coagulopathy may mask an underlying pseudocholinesterase deficiency.

  • Mechanical ventilatory support is the mainstay of treatment until respiratory muscle paralysis spontaneously resolves. Recovery eventually occurs as a result of passive diffusion of succinylcholine away from the neuromuscular junction.

  • Administration of cholinesterase inhibitors, such as neostigmine, is controversial for reversing succinylcholine-related apnea in patients who are pseudocholinesterase deficient. The effects may be transient, possibly followed by intensified neuromuscular blockade.

NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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