What is AChE (Acetylcholinesterase)?
Acetylcholinesterase (AChE) is a special enzyme that breaks down acetylcholine (ACh) — a chemical messenger (neurotransmitter) responsible for carrying signals between nerves and muscles in the nervous system.
Without AChE, acetylcholine would keep stimulating the nerves, causing continuous muscle contractions and affecting normal nerve communication.
The AChE test is mainly done for two important reasons:
- Prenatal screening (amniotic fluid test): To help detect neural tube defects (NTDs) in the fetus such as spina bifida or anencephaly.
- Neurological and toxicology studies: To assess nerve and muscle function or to diagnose poisoning by organophosphate pesticides or nerve agents, which block the enzyme’s activity.
Where is AChE Produced in the Body?
AChE is naturally produced in several parts of the body, including:
- Neurons (nerve cells): Main site of production, especially at neuromuscular junctions — the points where nerves connect to muscles.
- Red Blood Cells (RBCs): AChE is also found in RBC membranes and helps in diagnosing poisoning cases.
- Brain tissues: Present throughout the nervous system to control signal transmission.
- Amniotic fluid (during pregnancy): When the fetus has an open neural defect, AChE leaks from fetal neural tissue into the amniotic fluid — making it detectable through the test.
Main Functions and Importance of AChE
AChE plays several vital roles in the nervous and muscular systems:
- 1. Breakdown of Acetylcholine:
It stops nerve impulses by quickly breaking down acetylcholine after a nerve signal has been transmitted. This prevents continuous nerve stimulation. - 2. Muscle Control:
After every muscle contraction, AChE ensures that the muscle relaxes properly by clearing acetylcholine from the nerve endings. - 3. Prenatal Screening Role:
The enzyme’s presence in amniotic fluid can indicate neural tube defects in a developing fetus, making it an important test in pregnancy. - 4. Toxicology Use:
Organophosphate compounds (found in certain insecticides or nerve gases) block AChE, leading to dangerous accumulation of acetylcholine. Measuring AChE levels helps diagnose and manage such poisoning cases.
Causes of Low AChE Levels
Low AChE activity in the blood may occur due to:
- Organophosphate poisoning: Exposure to pesticides or nerve agents that inhibit AChE.
- Genetic enzyme deficiency: Some people inherit conditions that reduce AChE production.
- Severe liver disease: Since the enzyme is synthesized in the liver, liver damage can lower AChE levels.
Symptoms of Low AChE Levels
When AChE levels are too low, acetylcholine builds up in the body, causing overstimulation of nerves and muscles. Common symptoms include:
- Muscle twitching or spasms
- Muscle weakness or paralysis
- Difficulty breathing (due to respiratory muscle paralysis)
- Excessive salivation or sweating
- Pinpoint pupils (common in pesticide poisoning cases)
If untreated, severe poisoning can lead to respiratory failure — a life-threatening emergency.
Causes of High AChE Levels
High AChE levels are usually seen in amniotic fluid during pregnancy and indicate potential fetal abnormalities such as:
- Neural Tube Defects (NTDs):
Open defects in the fetus’s brain or spinal cord cause leakage of AChE into the amniotic fluid. - False-positive elevations:
Sometimes, levels may appear falsely high due to contamination of the sample with fetal blood or other biological material.
Symptoms Linked to High AChE Levels (During Pregnancy)
The mother usually does not experience any symptoms.
However, a high AChE level in the amniotic fluid suggests that the fetus may have:
- Spina bifida: An open spinal defect where the spinal cord doesn’t close properly.
- Anencephaly: A severe defect where major parts of the brain and skull are missing.
- Other neural tube defects (NTDs): Open defects of the brain or spinal cord that can be detected early through testing.
Reference Ranges of AChE
AChE levels vary depending on the type of sample:
- Amniotic Fluid AChE:
Normally absent.- Positive result: Indicates a neural tube defect, especially if AFP (Alpha-Fetoprotein) levels are also high.
- Blood AChE (RBC levels):
- Normal Range: Approximately 3,100 – 6,500 U/L (values may differ between labs).
- Decreased levels: Suggest organophosphate poisoning or enzyme deficiency.
Sample Type Required
The sample type depends on the purpose of testing:
- Amniotic fluid sample:
Used in prenatal screening to detect neural tube defects in the fetus. - Blood sample (plasma or RBCs):
Used in neurological or toxicological evaluations to check for poisoning or nerve function issues.
Test Preparation
- For pregnant women:
Amniotic fluid is usually collected through amniocentesis, typically performed between the 15th and 20th week of pregnancy. No special preparation is required, but it should be done under medical supervision. - For blood AChE testing:
A simple blood sample is taken.
Patients should inform the doctor about any chemical exposure or pesticide contact before the test.
When to Consult a Doctor
You should consult a doctor if:
- You experience muscle twitching, difficulty breathing, or weakness after pesticide exposure.
- You are pregnant and your AFP test shows abnormal results — your doctor may recommend an AChE test to confirm.
- There is suspected nerve agent exposure or unexplained neurological symptoms.
Important Word Explanations
- Acetylcholine (ACh): A neurotransmitter that carries signals between nerves and muscles.
- Neural Tube Defects (NTDs): Birth defects affecting the brain, spine, or spinal cord (like spina bifida).
- Organophosphate: A group of chemicals found in some pesticides that can block AChE activity.
- Amniotic Fluid: The protective liquid surrounding the fetus during pregnancy.
- Anencephaly: A severe birth defect involving the absence of major parts of the brain and skull.
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