This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Central Nervous System, Subject name: Pediatrics
Which marker is increased in amniotic fluid in neural tube defects? 
Select and explain. 
A. a fetoprotein, B. Acetylcholinesterase, C. bhCG, D. All of the above
A: a fetoprotein
Answer: A: a fetoprotein 
Explanation: Ans. is 'a' & 'b' i.e., a fetoprotein & Acetylcholinesterase * In intra embryonic life, neural tube is open at both end and freely communicate with amniotic cavity. Failure of closure of neural tube results in persistent of this communication. This allows excretion of following fetal substances into amniotic cavity -1) Alpha - fetoprotein2) Acetylcholinesterase* These serve as biochemical markers for NTDs for prenatal diagnosis.* In patients with elevated amniotic fluid AFP to differentiate between NTD and abdominal wall defect, acetylcholinesterase and pseudocholinesterase are measured.MarkerNeural tube defectAbdominal wall defectAcetylcholinesteraseHighLowPseudocholinesteraseLowHighRatio of Ach/ pseudocholinesterase>0.14<0.14