<prompt> Increase acetylcholinesterase in amniotic fluid indicatesOpen neural tube defectsOesophageal atresiaDown syndromeEdward syndrome  <response>: Prenatal diagnosis of neural tube defectIn intra embryonic life, neural tube is open at both end and freely communicate with amniotic cavity.Failure of closure of neural tube results in persistant of this communication.This allows excretion of following fetal substances into amniotic cavity -Alpha - fetoproteinAcetylcholinesteraseThese serve as biochemical marmkers for NTDs for prenatal diagnosis. 