Question:medium
Which of the following is the most specific marker for neural tube defects?
Which of the following is the most specific marker for neural tube defects?
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AFP screens, but which neural enzyme in amniotic fluid actually confirms an open NTD?
Updated On: Jun 24, 2026
- Acetylcholinesterase
- Pseudocholinesterase
- Alpha fetoprotein (AFP)
- Human chorionic gonadotrophin (HCG)
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The Correct Option is A
Solution and Explanation
The trick here is the word specific. Two markers point toward an open neural tube defect, but they do not perform the same job. Alpha fetoprotein is the screening marker: when the fetal neural tube is open, AFP spills into amniotic fluid and maternal serum, so maternal serum AFP goes up. The problem is that AFP also rises for many unrelated reasons, such as gastroschisis, twins, miscalculated dates, or fetal death, so a high value cannot prove an NTD.
Acetylcholinesterase is the confirmatory marker. It is an enzyme of nervous tissue, so it leaks into the amniotic fluid only when neural tissue is genuinely exposed, as in an open spina bifida or anencephaly. Because it is tied specifically to exposed neural tissue, detecting it in amniotic fluid is much more specific for an open neural tube defect than AFP. In practice, a raised maternal AFP is followed up by an amniotic AChE assay to confirm.
The other two choices do not belong. Pseudocholinesterase reflects liver synthesis and drug metabolism, not neural defects. HCG is a placental hormone used in Down syndrome screening, with no role in confirming NTDs.
Therefore the most specific marker is acetylcholinesterase.
\[\boxed{\text{Acetylcholinesterase}}\]
Acetylcholinesterase is the confirmatory marker. It is an enzyme of nervous tissue, so it leaks into the amniotic fluid only when neural tissue is genuinely exposed, as in an open spina bifida or anencephaly. Because it is tied specifically to exposed neural tissue, detecting it in amniotic fluid is much more specific for an open neural tube defect than AFP. In practice, a raised maternal AFP is followed up by an amniotic AChE assay to confirm.
The other two choices do not belong. Pseudocholinesterase reflects liver synthesis and drug metabolism, not neural defects. HCG is a placental hormone used in Down syndrome screening, with no role in confirming NTDs.
Therefore the most specific marker is acetylcholinesterase.
\[\boxed{\text{Acetylcholinesterase}}\]
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