Comparison of two methods for amniotic fluid cholinesterases identification in the qualitative test for prenatal diagnosis of neural tube defects

Abstract

Neural tube defects (NTD) are one of the more common congenital abnormalities with a generally accepted multifactorial origin, including a persistent environmental factor as well as a genetic factor, but with the precise cause still not known. Prenatal diagnosis of NTD uses a marker that is not a product of a defective gene or an abnormal chromosome, but is based upon the detection of elevated a,-fetoprotein (AFP) in the amniotic fluid [l]. The introduction of the qualitative amniotic fluid acetylcholinesterase test, in 1979, by Smith et al and Chubb et al [2,3] has gained wide acceptance as a secondary biochemical diagnostic test for the prenatal detection of NTD, thus improving the accuracy of the diagnosis. Qualitative description of the type of acetylcholinesterase in human amniotic fluid shows a typical form of this enzyme only in cases of open neural tube defects, but not in normal pregnancies [4-61. Gel electrophoresis separates non-specific cholinesterase from acetylcholinesterase on the basis of differential mobility: amniotic fluid from normal pregnancies has a single band which is a non-specific cholinesterase (ChE; EC 3.1.1.8), while NTD pregnancies have, additionally, a slightly faster-moving band which is acetylcholinesterase (AChE; EC 3.1.1.7) [7-121. AChE may be distinguished, additionally, from the non-specific ChE by the response to specific inhibitors [13]. AChE was originally chosen as a potential biochemical marker of NTD because of changes in its concentration associated with the development of the nervous