Question

Which is the best marker for an open neural tube defect?

• A. Acetylcholinesterase
• B. Pseudocholinesterase
• C. Alpha-fetoprotein (AFP)
• D. hCG

Hint:

AFP screens, but a neural-specific enzyme confirms an open defect.

Answer 1

The Correct Option is A

Approach this by separating screening from confirmation. An open neural tube defect spills fetal nervous-system contents into the amniotic fluid, so the ideal marker is one that is unique to neural tissue.

Alpha-fetoprotein is the first thing measured. It is produced by the fetal liver and yolk sac, and high levels in maternal serum or amniotic fluid flag a possible open defect. The catch is poor specificity: AFP also climbs with twins, ventral wall defects such as gastroschisis, intrauterine death, and simple dating errors. A raised AFP therefore raises suspicion but cannot prove an NTD.

To confirm, the laboratory looks for amniotic fluid acetylcholinesterase. This enzyme is essentially restricted to neural tissue, so finding it in the amniotic fluid points directly at exposed, open neural tube. Its presence converts a suspicious AFP into a confident diagnosis, which is exactly why it is regarded as the best (most specific) marker.

The remaining choices do not belong to neural screening at all. Pseudocholinesterase is a plasma enzyme relevant to prolonged paralysis after succinylcholine, and hCG is a placental hormone used in Down syndrome and trophoblastic disease workups.
\[\boxed{\text{Acetylcholinesterase}}\]