Pseudocholinesterase deficiency is a condition that causes increased sensitivity to certain muscle relaxant drugs used during general anesthesia (choline esters). These drugs relax the muscles used for movement, including those used for breathing. Normally, the muscles are able to move again a few minutes after the drugs are given. People with pseudocholinesterase deficiency may not be able to move or breathe on their own for a few hours after these drugs are given. They therefore may need mechanical ventilation until the drugs are cleared from the body. People with this condition may also have increased sensitivity to other types of drugs as well as to some agricultural pesticides.

Pseudocholinesterase deficiency can be inherited (genetic) or acquired. When it is inherited, it is autosomal recessive and caused by mutations in the BCHE gene. Acquired pseudocholinesterase deficiency may have various causes such as chronic infection, kidney or liver disease, malnutrition, major burns, cancer, or various medications.

Inherited pseudocholinesterase deficiency can be caused by mutations in the BCHE gene. This gene provides instructions for making the pseudocholinesterase enzyme, known as butyrylcholinesterase. This enzyme is made by the liver and circulates in the blood. It is involved in breaking down (metabolizing) choline ester drugs. Mutations that cause pseudocholinesterase deficiency either impair the function or production of butyrylcholinesterase. This impairs the body's ability to effectively metabolize choline ester drugs, leading to the abnormally prolonged effects of these drugs.

Acquired pseudocholinesterase deficiency is not inherited and cannot be passed to the next generation. This form of the condition is caused by impairment of the enzyme's function due to factors such as kidney or liver disease, malnutrition, major burns, cancer, or certain drugs.

The inherited form is autosomal recessive. This means that to be affected, a person must have a mutation in both copies of the responsible gene (BCHE) in each cell. Affected people inherit one mutated copy of the gene from each parent, who is referred to as a carrier. Carriers of an autosomal recessive condition typically do not have any signs or symptoms (they are unaffected). When 2 carriers of an autosomal recessive condition have children, each child has a:

• 25% chance to be affected
• 50% chance to be an unaffected carrier like each parent
• 25% chance to be unaffected and not a carrier

In some cases, carriers of BCHE gene mutations take longer than usual to clear choline ester drugs from the body - but not as long as those with two mutated copies of the gene.

Acquired pseudocholinesterase deficiency is not inherited, occurring due to illness, injury, or certain medications.

People with pseudocholinesterase deficiency should warn their relatives to be tested before surgery since the condition is often inherited. People who have relatives who have died for unknown reasons during surgery should be screened for the deficiency prior to undergoing surgery.

People with known pseudocholinesterase deficiency should avoid exposure to sources of choline esters. Treatment of prolonged respiratory paralysis following surgery often involves mechanical ventilatory support until the paralysis resolves on its own. In most cases, recovery happens without the need for medical assistance.