Amniotic-fluid acetylcholinesterase as a possible diagnostic test for neural-tube defects in early pregnancy

Prenatal Genetic Testing and Screening: A Focused Review

Given the advancements in prenatal testing, child neurologists are becoming involved in earlier stages of patient care, often being consulted during the gestational stage rather than during the postnatal period. Thus, it is essential that pediatric neurologists understand the strengths and limitations of prenatal testing when counseling families. In this review we separate prenatal testing into screening and diagnostic testing. On the one hand, screening testing is noninvasive and does not have an increased risk for miscarriage. Diagnostic tests, on the other hand, are invasive and include chorionic villus sampling and amniocentesis. Understanding that screening tests are not diagnostic is imperative, therefore, attention should be placed on the positive and negative predictive values when interpreting results within the clinical context. Given their invasive nature, prenatal diagnostic tests increase the risk for complications such as miscarriage. Diagnostic tests include biochemical marker testing, enzyme testing, karyotype, microarray, whole exome sequencing, and whole genome sequencing. With each test, pretest and post-test counseling is crucial for informed decision making, and the strengths and limitations should be discussed when obtaining consent. Prior to obtaining testing, clinicians must consider unexpected and unrelated findings of testing and must acknowledge that the patient always has the option to decline the test.

Understanding False Negative in Prenatal Testing

A false negative can happen in many kinds of medical tests, regardless of whether they are screening or diagnostic in nature. However, it inevitably poses serious concerns especially in a prenatal setting because its sequelae can mark the birth of an affected child beyond expectation. False negatives are not a new thing because of emerging new tests in the field of reproductive, especially prenatal, genetics but has occurred throughout the evolution of prenatal screening and diagnosis programs. In this paper we aim to discuss the basic differences between screening and diagnosis, the trade-offs and the choices, and also shed light on the crucial points clinicians need to know and be aware of so that a quality service can be provided in a coherent and sensible way to patients so that vital issues related to a false negative result can be appropriately comprehended by all parties.

Combined screening for open spina bifida at 11-13 weeks using fetal biparietal diameter and maternal serum markers

OBJECTIVE

Screening at 11-13 weeks with ultrasound biparietal diameter (BPD) can detect half of open spina bifida cases. Maternal serum α-fetoprotein (AFP) levels at 15-19 weeks are increased 3- to 4-fold, in open spina bifida. We assessed whether combined screening using BPD, AFP, and other serum markers at 11-13 weeks would increase detection.

STUDY DESIGN

Maternal AFP levels were measured on serum stored at 11-13 weeks in 44 open spina bifida and 182 unaffected pregnancies, and results were expressed in multiples of the median (MoM) for gestational age. All samples had been measured for free β-human chorionic gonadotropin (β-hCG) and pregnancy-associated plasma protein (PAPP)-A. A multivariate Gaussian model was used to predict screening performance from the serum data and BPD measurements on 80 cases, including 36 previously published.

RESULTS

The median AFP level in cases was 1.201 MoM, significantly higher than in unaffected pregnancies (P < .01, 1 tail). The median free β-hCG was significantly reduced to 0.820 MoM (P < .02), but the median PAPP-A was similar in cases and controls. Modeling predicted the following: BPD alone would detect 50% of cases for a 5% false-positive rate or 63% for 10%; adding AFP increases detection by 2%; and a combined test with BPD, AFP, and free β-hCG detects 58% for 5% or 70% for 10%.

CONCLUSION

Combining AFP and BPD with free β-hCG as part of first-trimester aneuploidy screening would also allow early detection about two-thirds of cases with open spina bifida.

Amniotic fluid glial fibrillary acidic protein (AF-GFAP), a biomarker of open neural tube defects

OBJECTIVE

Neural tube defects (NTDs) are usually identified by ultrasonography and confirmed by alpha-fetoprotein (AFP) assay and acetylcholinesterase (AchE) electrophoresis in amniotic fluid. Yet, both of these biomarkers can be found positive in other etiologies. Here, amniotic fluid glial fibrillary acidic protein (AF-GFAP), which was identified by a proteomic study, is shown to be a useful biomarker for NTD diagnosis.

METHOD

Amniotic fluid glial fibrillary acidic protein was measured by an ELISA assay in 138 cases of NTDs. Seventy samples from normal pregnancies used as controls and 27 samples giving false positive or false negative results either for AchE or AFP and corresponding to fetal death (n = 8), gastroschisis (n = 8), and unexplained etiologies (n = 11) were also tested.

RESULTS

Whatever the gestational age, GFAP was below 0.2 ng/mL in control samples, whereas 99.1% of open NTDs (29/29 in the anterior NTD group and 80/81 in the spina bifida group) were above this threshold. Closed NTDs were all negative (28/28). None of the other samples tested were positive, except in case of fetal death (8/8).

CONCLUSIONS

Amniotic fluid glial fibrillary acidic protein is a sensitive biomarker for open NTD diagnosis with a good negative predictive value for closed NTD. Compared with AFP and AchE, our results indicate that AF-GFAP alone is more efficient than this classical association.

Perfusion immunoassay for acetylcholinesterase: analyte detection based on intrinsic activity

A quantitative, two-column, HPLC-based assay requiring only 30 min to complete is reported. Amniotic fluid proteins are first fractionated on a size-exclusion column; the fraction containing the M(r) 280,000 neural acetylcholinesterase (AChE) is then diverted to a second column, an ImmunoDetection cartridge derivatized with an anti-AChE antibody. The immobilized antibody traps the enzyme, then substrate is flowed through the cartridge and the product is detected. For a positive result, the enzyme must have a molecular mass corresponding to the neural-AChE, be recognized by the antibody and be active in converting the substrate into product. The assay is sensitive in the clinically relevant range. The method provides rapid quantitative analysis using an automated instrument projected to be suitable for screening large numbers of samples.

Alpha-fetoprotein and acetylcholinesterase activity in first- and early second-trimester amniotic fluid

Normal ranges of amniotic fluid alpha-fetoprotein (AFP) and acetylcholinesterase activity (AChE) are described for gestational weeks 11-14 using rocket gel immunoelectrophoresis for AFP quantitation and a monoclonal antibody (4F19) enzyme antigen immunoassay for AChE activity measurement. The normal ranges were established by the examination of 281 amniotic fluid samples from 281 normal pregnancies. AFP was found to increase from a median level of 14.0 MIU/l at 11 weeks to a maximum at 13 weeks (median = 18.0 MIU/l) (P < 0.05), thereafter falling (not significant). No AChE test result exceeded 4.8 nkat/l. In addition, AFP and AChE values for three cases of fetal malformation, identified by the biochemical analyses of amniotic fluid, are given. These cases included two fetuses with a neural tube defect and one fetus with an abdominal wall defect. Amniocentesis was performed at 10, 11, and 14 weeks, respectively. The AFP and AChE values were all high.

Muscarinic acetylcholine responses in the early embryonic chick retina

The action of acetylcholine on cytoplasmic Ca2+ concentration ([Ca2+]i) was studied in early embryonic chick retinae. Whole neural retinae were isolated from embryonic day 3 (E3) chicks and loaded with a Ca(2+)-sensitive fluorescent dye (Fura-2). Increases in [Ca2+]i were evoked by the puff application of acetylcholine at concentrations higher than 0.1 microM. The Ca2+ response became larger in a dose-dependent manner up to 10 microM of acetylcholine applied. The rise in [Ca2+]i was not due to the influx of Ca2+ through calcium channels, but to the release of Ca2+ from internal stores. A calcium channel antagonist, nifedipine, which completely blocks the Ca2+ rise caused by depolarization with 100 mM K+, had no effects on the acetylcholine response and the Ca2+ response to acetylcholine occurred even in a Ca(2+)-free medium. The Ca2+ response to acetylcholine was mediated by muscarinic receptors. Atropine of 1 microM abolished the response to 10 microM acetylcholine, whereas d-tubocurarine of 100 microM had no effects. Two muscarinic agonists, muscarine and carbamylcholine (100 microM each), evoked comparable responses with that to 10 microM acetylcholine. The developmental change of the muscarinic response was examined from E3 to E13. The Ca2+ response to 100 microM carbamylcholine was intense at E3-E5, then rapidly declined until E8. The muscarinic Ca2+ mobilization we found in the early embryonic chick retina may be regarded as a part of the "embryonic muscarinic system" proposed by Drew's group, which appears transiently and ubiquitously at early embryonic stages in relation to organogenesis.

Antenatal diagnosis of pediatric surgical anomalies. Counseling the family

Improvements in screening and diagnostic techniques now mean that hundreds of congenital anomalies can be antenatally diagnosed. It is, however, impossible and inappropriate to submit all pregnant women to a barrage of investigations. Screening is necessary before specific invasive investigations are initiated. These include history, physical examination, MS-AFP screening, estriol and hCG screening, and a Level II ultrasonography scan. Once at-risk pregnancies have been identified, a multidisciplinary team approach is commenced and further studies including Level II ultrasonography, amniocentesis, chorionic villus sampling, or cordocentesis can be performed so that an accurate diagnosis is available. Counseling of the parents throughout is essential so that appropriate decisions regarding this and further pregnancies can be made.

The association between 'faint-positive' amniotic fluid acetylcholinesterase and fetal malformations

The finding of a 'faint-positive' acetylcholinesterase band in amniotic fluid samples of women at 15 weeks' gestation or above is associated with an increased risk of fetal abnormalities, most commonly gastroschisis. This finding warrants a targeted sonographic evaluation, in order to rule out significant fetal malformations.

A comparison of amniotic fluid alpha-fetoprotein and acetylcholinesterase in the prenatal diagnosis of open neural tube defects and anterior abdominal wall defects

Amniotic fluid samples received for routine prenatal diagnosis of open neural tube defects were used for a study to compare amniotic fluid acetylcholinesterase (AChE) determination using a monoclonal antibody (4F19) enzyme antigen immunoassay and amniotic fluid alpha-fetoprotein (AFP) measurement as diagnostic tests for open neural tube defects. The study was based on 9964 women with singleton pregnancies and known outcome (including 6 with anencephaly and 18 with open spina bifida) having an amniocentesis at 14-23 weeks of gestation. The AChE immunoassay yielded detection rates for anencephaly of 100 per cent (95 per cent confidence interval (CI) 54.07-100 per cent), for open spina bifida of 100 per cent (95 per cent CI 81.47-100 per cent), for anterior abdominal wall defects of 20 per cent (95 per cent CI 0.51-71.64 per cent), and a false-positive rate of 0.22 per cent (95 per cent CI 0.14-0.34 per cent) excluding anencephaly, open spina bifida, and anterior abdominal wall defects. For similar detection rates the false-positive rate of the AFP test was significantly higher, 0.74 per cent (95 per cent CI 0.58-0.94 per cent). On the basis of these findings, it is recommended that the technically simple AChE immunoassay should be used on all samples; the AFP test should only be used on the 0.5 per cent of the samples with concentrations of AChE activity > or = 8.5 nkat/l for clear samples and blood-stained samples becoming clear after centrifugation, and > or = 25.0 nkat/l for blood-stained samples that are discoloured after centrifugation; an AFP cut-off level of 2.0 MOM is recommended for this policy. Thereby, the detection rates for anencephaly, open spina bifida, and anterior abdominal wall defects would be 100, 100, and 20 per cent, respectively (95 per cent CIs 54.07-100, 81.47-100, and 0.51-71.64 per cent, respectively), and the false-positive rate would be 0.08 per cent (95 per cent CI 0.03-0.16 per cent) (excluding anencephaly, open spina bifida, and anterior abdominal wall defects).

First-trimester amniotic fluid and extraembryonic coelomic fluid acetylcholinesterase electrophoresis

Acetylcholinesterase (AChE) gel electrophoresis was performed on samples of amniotic fluid and extraembryonic coelomic fluid obtained by high resolution transvaginal ultrasound-guided amniocentesis from 38 women between 8 and 12 weeks of pregnancy. AChE was positive in 33 per cent (12/36) of the amniotic fluid samples; the percentage of positive results decreased as gestation advanced. AChE was positive in 32 per cent (9/28) of the extraembryonic coelomic fluid samples. In 81 per cent (21/26) of matched samples, the AChE results were identical in the two fluids. Amniotic fluid and extraembryonic coelomic fluid AChE electrophoresis cannot be used to diagnose neural tube defects prior to 12 weeks of gestation.

Cholinesterases exhibiting aryl acylamidase activity in human amniotic fluid

Acetylcholinesterase (EC 3.1.1.7) and butyrylcholinesterase (EC 3.1.1.8) in human amniotic fluid were estimated in the presence of selective inhibitors. Amniotic fluid cholinesterases (mixture of acetylcholinesterase and butyrylcholinesterase) purified by procainamide-Sepharose affinity chromatography exhibited aryl acylamidase activity which was sensitive to serotonin inhibition (a property of aryl acylamidases associated with both acetyl- and butyrylcholinesterases) and tyramine activation (shown exclusively by aryl acylamidase associated with butyrylcholinesterase). Tyramine activation was unaffected in the presence of the selective acetylcholinesterase inhibitor BW284C51 whereas it was abolished in the presence of the selective butyrylcholinesterase inhibitor ethopropazine, suggesting the presence of both types of aryl acylamidases in amniotic fluid, one associated with acetylcholinesterase and the other associated with butyrylcholinesterase. Butyrylcholinesterase and the associated aryl acylamidase activity in the affinity purified enzyme was selectively immunoprecipitated by a polyclonal antibody raised against human serum butyrylcholinesterase. Estimation of the activity ratio of acetylcholinesterase to butyrylcholinesterase in a few samples of amniotic fluid showed that this could vary depending on the butyrylcholinesterase arising from contaminating blood in the samples. Gel electrophoresis under non-denaturing conditions and enzyme staining showed that butyrylcholinesterase band was detectable on the gel in all the samples whereas acetylcholinesterase band was below detectable levels in normal samples but visible in samples from pregnancies of neural tube defect fetuses. It is suggested that the use of selective cholinesterase inhibitors along with gel electrophoresis and immunoprecipitation studies may be useful in the assessment of cholinesterase activities in human amniotic fluid.

Rapid and sensitive discriminating determination of acetylcholinesterase activity in amniotic fluid with a choline sensor

A simple method for the separate determination of acetylcholinesterase and butyrylcholinesterase activities in amniotic fluid is reported. This determination is performed with an enzyme electrode involving an immobilized choline oxidase membrane associated with the amperometric detection of hydrogen peroxide. Acetylcholine or butyrylcholine, in the presence of samples containing acetylcholinesterase or butyrylcholinesterase are specifically hydrolyzed, the formation of choline being detected vs time by the sensor with no need for a selective inhibitor. The dynamic linear ranges for acetylcholinesterase and butyrylcholinesterase are respectively 100 microU to 10 mU and 30 microU to 3 mU per ml sample.

Presence of a soluble form of acetylcholinesterase in human ocular fluids

Samples of ocular fluid obtained from normal persons at necropsy and during eye surgery have been assayed for the presence of acetylcholinesterase. Measurable levels could be detected in all samples examined, but levels of acetylcholinesterase in vitreous humour were consistently higher than those in aqueous humour, indicating a possible retinal origin. Polyacrylamide gel electrophoresis revealed that the enzyme of ocular fluid had the same mobility as that of acetylcholinesterase from cerebrospinal fluid. It is probable that acetylcholinesterase is secreted from neuronal structures in the retina into the ocular fluid in an analogous manner to the secretion of acetylcholinesterase from brain neurones into cerebrospinal fluid.

A co-twin fetus papyraceus as a cause of elevated AFP and acetylcholinesterase in the amniotic fluid of the normal co-twin

An elevated amniotic fluid alpha-fetoprotein (AF-AFP) level together with a positive acetylcholinesterase (AChE) band is strongly predictive of neural tube defect (NTD) in the fetus. We report such results in a pregnancy in which the fetus was found to be normal after termination. Among the placental fragments was found a sac containing a prenatally undetected co-twin fetus papyraceus. We suggest that pregnant women with such laboratory results but lacking sonographic evidence of NTD should have a high-level untrasonographic investigation, as well as a thorough pathologic examination of both placenta and fetus in cases of termination.

Cholinesterases during development of the avian nervous system

1. Long before onset of synaptogenesis in the chicken neural tube, the closely related enzymes butyrylcholinesterase (BChE) and acetylcholinesterase (AChE) are expressed in a mutually exclusive manner. Accordingly, neuroblasts on the ventricular side of the neural tube transiently express BChE before they abruptly accumulate AChE while approaching the outer brain surface. 2. By exploiting AChE as a sensitive and early histochemical differentiation marker, we have demonstrated complex polycentric waves of differentiation spreading upon the cranial part of the chicken neural tube but a smooth rostrocaudal wave along the spinal cord. Shortly after expression of AChE, these cells extend long projecting neurites. In particular, segmented spinal motor axons originate from AChE-positive motoneurones; they navigate through a BChE-active zone within the rostral half of the sclerotomes before contacting BChE/AChE-positive myotome cells. At synaptogenetic stages, cholinesterases additionally are detectable in neurofibrillar laminae foreshadowing the establishment of cholinergic synapses. 3. In order to elucidate the functional significance of cholinesterases at early stages, we have investigated specific cholinesterase molecules and their mechanisms of action in vivo and in vitro. A developmental shift from the low molecular weight forms to the tetramers of both enzymes has been determined. In vitro, the addition of a selective BChE inhibitor leads to a reduction of AChE gene expression. Thus, in vivo and in vitro data suggest roles of cholinesterases in the regulation of cell proliferation and neurite growth. 4. Future research has to show whether neurogenetic functioning of cholinesterases can help to understand their reported alterations in neural tube defects, mental retardations, dementias and in some tumours.

Amniotic fluid acetylcholinesterase in the prenatal diagnosis of open neural tube defects and abdominal wall defects: a comparison of gel electrophoresis and a monoclonal antibody immunoassay

Stored amniotic fluid samples collected in Oxford and East Birmingham as part of the Collaborative Acetylcholinesterase Study were assayed for the presence of acetylcholinesterase (AChE) using a monoclonal antibody (4F19) enzyme antigen immunoassay. These results were compared with the results of a gel AChE which had been performed earlier. A total of 5689 samples from singleton pregnancies were analysed (including 36 with anencephaly, 77 with open spina bifida and 17 with anterior abdominal wall defects). The gel test yielded detection rates of 97% for anencephaly, 99% for open spina bifida and 94% for abdominal wall defects; the false positive rate (excluding pregnancies associated with serious abnormalities, miscarriages and intrauterine deaths) was 0.24%. The monoclonal test yielded similar results; using appropriate cut-off values to allow for differences in acetylcholinesterase levels in blood stained and clear samples, a similar false-positive rate of 0.22% was associated with detection rates of 97%, 95% and 71% respectively for the three types of defect. Although the detection rates and the false positive rate were slightly higher for the gel test, a result that might be explained by a decrease in AChE activity caused by storage of the samples, the monoclonal test has the advantages of requiring less interpretative expertise, it can be performed on a larger number of samples a day and it is not affected by contamination with fetal calf serum.

Amniotic fluid acetylcholinesterase measurement in the prenatal diagnosis of open neural tube defects. Second report of the Collaborative Acetylcholinesterase Study

Seventeen centres from Australia, Britain, France, and the United States collaborated in a study to compare amniotic fluid acetylcholinesterase (AChE) determination by gel electrophoresis and amniotic fluid alpha-fetoprotein (AFP) measurement as diagnostic tests for open neural tube defects. The study was based on 32,642 women with singleton pregnancies (including 428 with open spina bifida and 238 with anencephaly) who had an amniocentesis at 13-24 weeks' gestation. The AChE test yielded a detection rate for open spina bifida of 99 per cent (95 per cent confidence interval 98-100 per cent), 98 per cent for anencephaly (95 per cent confidence interval 96-100 per cent), and a false-positive rate of 0.34 per cent (95 per cent confidence interval 0.28-0.40 per cent) excluding miscarriages, intrauterine death, and serious fetal abnormalities. The false-positive rate was 0.30 per cent among the 13 centres that used a specific AChE inhibitor in the test. Comparable rates for the AFP test were less favourable. (For example, the open spina bifida detection rate was 90 per cent and the false-positive rate was 0.46 per cent using the cut-off levels specified in the U.K. Collaborative AFP Study.) The AChE false-positive rate was lower in samples that were not bloodstained (0.16 per cent) than in those that were (2.4 per cent). It was higher in women who had an amniocentesis on account of a raised maternal serum AFP level (0.56 per cent) than in those who had one for other reasons (0.29 per cent). The best results were obtained by a combination of the two tests, an effective and economical policy being to perform the AFP measurement on all amniotic fluid samples and an AChE test on samples with AFP levels greater than or equal to 2.0 multiples of the normal median (about 5 per cent of all samples). Using this policy, the open spina bifida detection rate was 96 per cent and the false-positive rate was 0.14 per cent (0.06 per cent for samples that were not bloodstained and 1.2 per cent for those that were; 0.40 per cent for women with raised serum AFP levels and 0.09 per cent for other women). This policy offers a useful improvement to the prenatal diagnosis of open spina bifida.

Towards the prevention of neural tube defects

The value of maternal periconceptional vitamin supplementation in preventing the conception of fetuses with neural tube defects has yet to be assessed in a properly designed study. Avoidance of the birth of affected infants continues to rest on second-trimester maternal serum alphafetoprotein screening. The performance of screening programmes in achieving this objective is reviewed.

Evaluation and quality control of a monoclonal antibody based enzyme antigen immunoassay of acetylcholinesterase in amniotic fluid

We have evaluated a new monoclonal antibody based enzyme antigen immunoassay (EAIA) for acetylcholinesterase in amniotic fluid, intended for the detection of open fetal abnormalities, especially open neural tube defects. With a sample volume of 50 microliters, the detection limit is 0.7 nkat/l and linearity is found up to an amount 200-times the detection limit. CV's are less than or equal to 6.6% within assays and less than or equal to 10.3% between assays; recoveries averaged 103%. The upper limit of the reference range for amniotic fluids from non-affected pregnancies is 8.5 nkat/l for clear specimens and 25.0 nkat/l for haemolysed specimens. Amniotic fluid specimens from 1473 patients (1388 normal and 85 pathological pregnancies) were examined with both the new EAIA and the original procedure using a polyclonal rabbit antiserum. The two procedures showed identical sensitivities and specificities of about 100%, except for amniotic fluid samples containing haemolysed blood. For the latter the new EAIA showed a specificity of 100% compared to 55.6% for the original procedure. We conclude that the new EAIA is accurate and reproducible and shows, compared with the original procedure, an increased specificity in the analysis of amniotic fluid samples containing haemolysed blood.

Amniotic fluid acetylcholinesterase ratios in prenatal diagnosis of fetal abnormalities

This study examined 141 pregnancies with acetylcholinesterase in the amniotic fluid to determine if an acetylcholinesterase/pseudocholinesterase ratio cutoff could be set to distinguish between neural tube defects, ventral wall defects, other fetal defects, and pregnancy problems. Amniotic fluid specimens with positive or faintly positive acetylcholinesterase bands were studied. They were scanned and analyzed for the acetylcholinesterase/pseudocholinesterase ratio. In 62 of 65 fluid samples from open neural tube defects, the acetylcholinesterase/pseudocholinesterase ratios were greater than 0.13. All cases with ventral wall defects (n = 29), fetal blood contamination (n = 16), or fetal ascites (n = 2) had acetylcholinesterase/pseudocholinesterase ratios less than 0.13. Samples of cystic hygroma fluid (n = 10) had acetylcholinesterase/pseudocholinesterase ratios greater than 0.13. Two patients with fetal teratomas had intermediate values. All patients with normal outcomes but positive acetylcholinesterase had ratios of less than 0.12. Acetylcholinesterase/pseudocholinesterase ratios are a valuable part of a prenatal program to accurately diagnose fetal abnormalities.

Secretion of acetylcholinesterase and butyrylcholinesterase from the guinea-pig isolated ileum

1. Strips of longitudinal muscle from guinea-pig ileum, retaining Auerbach's plexus, were superfused with oxygenated Krebs solution. Addition of 50 mM KCl led to a pronounced Ca2+-dependent increase in the activities of both acetylcholinesterase and non-specific cholinesterase (butyrylcholinesterase) in the perfusate but with no change in lactate dehydrogenase activity. 2. No release of acetylcholinesterase, either spontaneous or K+-evoked was observed in tissue freed of the nerve plexus, although release of butyrylcholinesterase still occurred. 3. Carbachol induced a marked Ca2+-dependent increase in the release of acetylcholinesterase but had no effect on the release of butyrylcholinesterase or lactate dehydrogenase. This carbachol-evoked increase in acetylcholinesterase release was blocked by hexamethonium but not by atropine. 4. Four readily soluble molecular forms of acetylcholinesterase and three soluble molecular forms of butyrylcholinesterase were present in innervated longitudinal muscle strips, but insignificant amounts of acetylcholinesterase were detected in denervated strips of muscle. Only one of the four molecular forms of acetylcholinesterase was recovered in the perfusates. 5. It is concluded that acetylcholinesterase is secreted from the nerves of Auerbach's plexus in response to depolarizing stimuli or to nicotinic cholinergic stimulation, while butyrylcholinesterase is secreted from non-neural elements, possibly the longitudinal muscle cells, of guinea-pig ileum in response to a depolarizing stimulus.

Prolonged elevation of alphafetoprotein and detectable acetylcholinesterase after death of an anomalous twin fetus

Persistence of elevated alphafetoprotein (AFP) levels and the presence of an acetylcholinesterase (AChE) band in amniotic fluid have been reported to occur up to 11 weeks following intrauterine fetal demise (IUFD) of one twin (Bass et al., 1986). We now report a case where such prolongation of these findings was observed in a case of unrecognized monochorionic, monoamniotic twinning, in which case cord entanglement resulted in IUFD at an estimated 10-12 weeks and 25-26 weeks. The fetus suffering early demise (Fetus B) had multiple congenital anomalies, including a neural tube defect. The presence of this defect and/or fetal demise and bleeding into the amniotic sac is entertained as continuing sources of documented elevated AChE and AFP 9-11 weeks after the initial fetal death. We re-emphasize the possibility of unrecognized twinning as a cause of abnormal maternal serum and amniotic fluid study results in the face of one apparently normal fetus.

Antenatal diagnosis of neural tube defects using a coated bead immunoassay for acetylcholinesterase in amniotic fluid

The development and validation of a coated bead immunoassay for amniotic fluid acetylcholinesterase is outlined. The assay has good precision (between assay CV of 6.8% within the normal range), and is linear up to 250 arbitrary units/L. The clinical validity of this assay has been assessed using a panel of amniotic fluid samples from normal and abnormal pregnancies. At an assay cut off level of 200 arbitrary units/L, all cases of neural tube defect-affected pregnancies were identified and the number of false positives was very small. False positives resulted from severe blood staining of the amniotic fluid. Since the monoclonal antibody used recognises red cell membrane acetylcholinesterase and the stored amniotic fluids had been frozen and thawed a number of times, the extent of this problem needs to be further assessed using freshly collected samples. The performance of this assay was found to be superior to the differential inhibitor colorimetric method and close to that of the electrophoretic procedure. The quantitative nature of the assay and the independence from operator technique makes it a useful adjunct to the measurement of amniotic fluid AFP in the prenatal diagnosis of neural tube defects.

Prevention and avoidance of congenital malformations

Many congenital abnormalities do not have either a Mendelian pattern of inheritance or an identifiable chromosome abnormality and are described as 'multifactorial' as it is assumed they are determined by several genes, each with added effects and modified to a greater or lesser extent by environmental factors. They include spina bifida and anencephaly, cleft lip or cleft palate or both, congenital heart defect and congenital dislocation of the hip, and they constitute a major community health problem. Developments in genetics, biochemistry and cytogenetics have presented new approaches to the prevention and avoidance of congenital abnormalities. The approaches available for the avoidance of congenital malformations include the avoidance of harmful environmental factors, the screening of the newborn and early treatment, genetic counselling and antenatal monitoring with selective termination. The prevention of neural-tube defects in 'high risk' mothers can be achieved by periconceptional vitamin supplementation. In Northern Ireland, of 438 fully supplemented women, only 4 (0.98%) infants or fetuses among 407 infants and fetuses examined had a neural-tube defect, whereas of 356 unsupplemented women, 16 (4.7%) infants or fetuses among 337 infants or fetuses examined had a neural-tube defect.

Amniotic fluid cholinesterase of valproate-induced exencephaly in the mouse: an animal model for prenatal diagnosis of neural tube defects

After a single administration of the antiepileptic drug valproic acid (VPA; i.p.:600 mg/kg) on day 8 of gestation in the mouse embryotoxicity and amniotic fluid (AF) cholinesterase (ChE) were evaluated on day 16 of gestation. VPA treatment induced an increase in embryolethality, neural tube defects (exencephaly), cleft palate, deformed vertebrae, open eyes, and a reduction in fetal weight. In VPA-exposed fetuses AF total ChE (TChE) activity of exencephalic fetuses was higher than that of normal fetuses. However, in 3 out of 110 normal fetuses of the control group TChE activity was found in the AF. There was no correlation between blood contamination of AF and its TChE activity, either in non-exencephalic control or treated embryos. Using ethopropazine as a "pseudo"-ChE inhibitor in vitro, the percentage of acetyl-ChE in blood-contaminated AF was similar to that of fetal rather than maternal serum, indicating that AF was contaminated with fetal and not with maternal blood. VPA-induced exencephaly in mice may provide an animal model to further investigate biochemical markers for prenatal diagnosis of neural tube defects.

S-100 protein and neuron-specific enolase in amniotic fluid as markers of abdominal wall and neural tube defects in the fetus

The aim of this study was to determine whether there is increased leakage of neuron-specific enolase (NSE) and S-100 protein into amniotic fluid in pregnancies with neural tube defects, since both these proteins are produced by neural tissue, and to compare the value of these substances for detecting such defects with that of the more conventional techniques of alpha-fetoprotein (AFP) and acetylcholinesterase (AChE) gel electrophoresis. Amniotic samples from 25 mid-pregnancies (15-17 weeks' gestation) with neural tube defects (14 with open spina bifida and 11 with anencephaly) and from seven mid-pregnancies with abdominal wall defects were compared with a control material consisting of 80 amniotic fluid samples from 80 consecutive mid-pregnancy amniocenteses, with normal karyotypes and AFP concentrations. All of the above cases of abnormalities were primarily detected through increased AFP levels in the amniotic fluid. Amniotic fluid samples from 13 pregnancies with fetuses with autosomal chromosomal abnormalities and seven amniotic fluid samples contaminated with blood were also included in the investigation. It is concluded from the results that the conventional AFP assay combined with AChE gel electrophoresis is the best method for screening amniotic fluid for neural tube defects and defects of the abdominal wall. Neither NSE nor S-100 assay alone proved to be superior for the detection of these cases in mid-trimester amniotic fluid. The S-100 assay, however, could give additional information in cases where AChE gel electrophoresis is not decisive; for example, in samples contaminated with blood.

Maternal serum alpha-fetoprotein is a marker for fetal anomalies in pediatric surgery

Maternal serum alpha-fetoprotein (MS-AFP) screening has become part of routine obstetric care. Although elevated MS-AFP was originally associated with neural tube defects (NTD), it is also able to detect several fetal anomalies of interest to a pediatric surgeon, ie, ventral abdominal wall defects, intestinal atresias, and sacrococcygeal teratomas. Previously, decreased MS-AFP had only been associated with fetal trisomies, but not surgically correctable lesions. In the present study, we review our recent experience with both elevated and decreased MS-AFP as a marker to detect fetal anomalies of concern to the pediatric surgeon. Forty-one fetal anomalies were associated with 333 pregnancies referred for follow-up after abnormal MS-AFP screening results from November 1985 through November 1986. One hundred ninety-six were elevated and 139 were decreased. In most cases, evaluation included counseling, repeat MS-AFP, level II ultrasound, and amniocentesis. This revealed elevated MS-AFP to be associated with 32 (16.3%) anomalies (2 NTD, 5 anencephalics, 5 ventral abdominal wall defects, 1 stage IV-S neuroblastoma, 1 renal anomaly, 1 ventriculomegaly, 15 fetal demises, and 2 fetal-maternal bleeds). Decrease in MS-AFP was associated with nine (6.4%) anomalies (2 congenital diaphragmatic hernias, 3 Down's syndrome, 1 Turner's syndrome, 2 duodenal atresias, and 1 choroid plexus cyst). In this study, MS-AFP detected several fetal anomalies known to be associated with abnormal MS-AFP and three anomalies not previously described (congenital diaphragmatic hernia, neuroblastoma, and choroid plexus cyst). Elevated as well as decreased MS-AFP are significant and should be pursued by a full prenatal evaluation.(ABSTRACT TRUNCATED AT 250 WORDS)

Neural tube defect-specific acetylcholinesterase: its properties and quantitation in the detection of anencephaly and spina bifida

Amniotic fluid from neural tube defect-affected pregnancies (NTD) contains three forms of acetylcholinesterase (AChE), the major species of which is present only in trace amounts in normal pregnancies or those associated with a non-NTD fetal malformation. The activity of this 'specific' AChE is increased 62-fold in the presence of NTD and its measurement provides a sensitive and specific test for the biochemical detection of this disorder. The sedimentation coefficient of 'NTD specific' AChE (10.3S) indicates that it is a tetrameric species, and that the two additional forms present, (4.0S and 5.5S) are monomer and dimer, respectively. Gel filtration studies also support these findings. Combining these data, the molecular masses of monomer, dimer and tetramer are shown to be 78, 126 and 256 kDa (+/- 10%). 'NTD-Specific' AChE does not react with the detergent Triton X-100, indicating that it is a soluble, and probably secreted, species without membrane associating properties.

Association of neural tube defects with omphalocele in chromosomally normal fetuses

Omphalocele is frequently associated with other congenital malformations or a chromosome abnormality. Previously published series of omphalocele have emphasized the association of congenital heart defects or chromosomal abnormalities. We present five cases of omphalocele with concurrent neural tube defect from among the 15 cases of omphalocele evaluated between 1981 and 1985. Fourteen of 15 were detected prenatally. A sixth case is presented in which both a neural tube defect and an omphalocele were suspected on a prenatal ultrasound, but only the latter was found on autopsy. We recommend that a systematic evaluation be performed on every fetus with an omphalocele to include amniotic fluid alpha fetoprotein, acetylcholinesterase levels, chromosome study, and careful ultrasonography looking for evidence of other abnormalities, especially neural tube defects, before counseling the parents.

Determination of neuron specific enolase in amniotic fluid and maternal serum for the prenatal diagnosis of fetal neural tube defects

Maternal serum neuron-specific enolase was tested as a marker for fetal nural tube defect. In around 50% of pregnancies with affected fetus the level was elevated. The increase was also found in the amniotic fluids. Normal fetal serum did not display elevation of neuron-specific enolase.

Spatiotemporal relationship of embryonic cholinesterases with cell proliferation in chicken brain and eye

Close relationships between acetylcholinesterase (AcChoEase; acetylcholine acetylhydrolase, true cholinesterase, EC, 3.1.1.7) and butyrylcholinesterase (BtChoEase, acylcholine acylhydrolase, pseudocholinesterase, EC, 3.1.1.8) with cell proliferation were observed in the early chicken brain. These include the following: BtChoEase is transiently accumulating in patchy fashion on the ventricular side of the neuroepithelium shortly before AcChoEase appears in cell bodies along the opposing mantle layer. The amount of BtChoEase in retina and brain is greatest in the early phase (E3-E5, or incubation periods of 3-5 days); in retina it decreases about 2 days later than in brain. However, AcChoEase expression increases with time, in inverse order to that of BtChoEase. In both tissues decrease of cell proliferation is closely followed by decrease in BtChoEase. A double-labeling technique of cholinesterase staining together with [3H]thymidine autoradiography reveals proliferation zones that are diffusely stained by BtChoEase but not by AcChoEase. Patches intensely stained for BtChoEase accompany clusters of cells in final stages of mitosis on their way to the differentiation zone, where they begin expressing AcChoEase. By applying different thymidine pulses, we identify an 11-hr lag from the last thymidine-uptake to full AcChoEase expression. (iv) These findings are confirmed by studying lens development, where areas of proliferation and differentiation are well separated. The spatiotemporal pattern of the transition of neuroblasts from a proliferating into a differentiating state correlates with the expression of BtChoEase just before and during mitosis and that of AcChoEase about 11 hr after mitosis. Thus cholinesterases could be involved in the regulation of this transition.

Causes of windowing-induced dysmorphogenesis (neural tube defects and early amnion deficit spectrum) in chicken embryos

Previous reports suggest that windowing the shells of chicken eggs during the first day of incubation frequently results in dysmorphogenesis of the central nervous system. We report here data that further delineate the neural tube defects associated with this animal model. In addition, we describe another birth defect syndrome associated with windowing: the early amnion deficit spectrum (EADS). Several components of the egg are altered structurally by windowing: the shell, outer and inner shell membranes, yolk, and air space at the blunt end of the egg. A new air space is formed over the embryo as the original one at the blunt end is obliterated. A series of studies (pH, oxygen and carbon dioxide tensions, relative humidity, temperature, and deformation of the yolk documented with magnetic resonance imaging) examining individual steps of the windowing procedure and additional techniques that stimulate windowing suggest that mechanical stress causes isolated neural tube defects and dehydration causes amnion defects. These amnion defects are associated with other embryonic abnormalities suggestive of deformations consistent with EADS.

Positive amniotic fluid acetylcholinesterase: distinguishing between open spina bifida and ventral wall defects

The ratio of amniotic fluid acetylcholinesterase to pseudocholinesterase was determined by scanning densitometry on 43 amniotic fluid samples with positive acetylcholinesterase associated with open fetal defects. The mean ratio was 0.587 (range 0.204 to 0.979) in 21 amniotic fluid samples from pregnancies affected with open spina bifida and 0.052 (range 0.026 to 0.075) in 12 pregnancies affected with ventral wall defects. These data confirm previous observations and indicate that scanning densitometry of electrophoretic gels is a useful method for distinguishing between open spina bifida and ventral wall defects in the fetus.

Determination of cholinesterase and acetylcholinesterase in amniotic fluid. Uses in prenatal diagnosis and quality control

The determination of acetylcholinesterase (AChE) has been shown to be as specific as alphafetoprotein (AFP) for the prenatal detection of open neural tube defects although AFP remains the method of choice. This paper describes a semi-automated technique for the analysis of acetylcholinesterase in amniotic fluid that: A) reduces the cost of the procedure; B) allows for a larger number of samples to be run at a time; and C) provides for more accurate and reproducible procedures and results. Six fetuses with neural tube defects (2 with gastroschisis and 3 where one twin was dead) were detected and found to have elevated AChE, TChE and 2 bands by electrophoresis. Quality control procedures using both pure enzyme and amniotic fluid with low and high levels of the enzyme are described. The analysis of 340 amniotic fluids of normal pregnancies indicates that the normal value for AChE is 5.17 +/- 2.63 mU/ml (97% confidence interval for the mean 4.84-5.49 mU/ml. A group of 27 abnormal pregnancies provides evidence that fetal vomiting and regurgitation, fetal demise, multiple cysts syndrome, idiopathic IUGR, arthrogryposis multiplex, hydrocephaly (stenosis of aqueductus), trisomy 21, trisomy 18, hydronephrosis, pyloric stenosis, heart malformation, ectopia cordis and multiple gestation produce elevated levels of pseudocholinesterase (PChE) in amniotic fluid. The use of pseudocholinesterase levels in amniotic fluid for prenatal diagnosis is proposed and discussed in view of its elevated levels in abnormal pregnancies where AChE is normal. The normal values for PChE are 23.86 mU/ml (mean) and 5.83 for standard deviation. Electrophoretic analysis was performed on all samples with values higher than one standard deviation above the mean.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential diagnosis of sonographically detected tumours in the fetal cervical region

Differential diagnosis of sonographically detected fetal neck tumours is difficult. The sonographic criteria for encephalomyelocele, lymphangioma/hygroma, teratoma, sarcoma, haemangioma, neuroblastoma and goitre are given on the basis of the authors' own observations and information from the literature. Elevation of alpha-fetoprotein in the amniotic fluid is a frequent but non-specific finding. Chromosome analysis after amniocentesis can be a useful supplementary procedure for assessing the prognosis and deciding upon the delivery procedure. Sonographic detection of a tumour in the fetal neck region enables preparations to be made for dystocia and postnatal dyspnoea of the newborn. The obstetrician must cooperate closely with paediatricians, neurologists, surgeons and ENT specialists.

Amniotic fluid gel acetylcholinesterase determination in prenatal diagnosis: dark field illumination as a method for improving the detection of precipitation bands

This paper describes a sensitive method for the detection of precipitation bands in the qualitative acetylcholinesterase (AChe) gel test. This method--dark field illumination--is compared with two existing methods of detection: epi-illumination of unstained gels and transillumination of dithio-oxamide stained gels. The comparison has been carried out on a selected series of 271 amniotic fluid samples, taken before the 22nd week of gestation. All 96 samples from normal pregnancies were scored as negative with all three visualization methods. For the detection of neural tube defects (NTD) and omphaloceles, dark field illumination proved to be more efficient than epi-illumination or dithio-oxamide staining. In case of another congenital defect, we obtained a positive result with dark field illumination, and a negative one with the other detection methods. It is concluded that dark field illumination was shown to be the most sensitive method for the detection of precipitation bands.

Prenatal diagnosis of neural-tube defects with a monoclonal antibody specific for acetylcholinesterase

An immunoassay for acetylcholinesterase (AChE), based on a monoclonal antibody (AE-2), gave the following results when applied to a panel of amniotic fluids: (a) among 651 samples with normal outcome and normal alphafetoprotein (AFP) values there were 2 (0.31%) false positives; (b) of 9 samples with normal outcome and raised AFP values 1 had a raised AChE titre; (c) all 48 samples from anencephaly cases had raised AChE values; (d) among 49 samples from open spina bifida cases (2 of which had normal AFP values), 48 had raised AChE titres. It is suggested that a monoclonal-antibody-based immunoassay may displace polyacrylamide gel electrophoretic analysis of AChE as a complementary test to AFP in prenatal diagnosis of neural-tube defects, since it is a quantitative test largely independent of operator skill and experience.

Maternal serum alpha-fetoprotein screening for neural tube defects. Report of a combined study in Germany and short overview on screening in populations with low birth prevalence of neural tube defects

The basis of maternal serum alpha-fetoprotein (AFP)-screening for neural tube defects is discussed. A report is given of a large scale screening study in the Federal Republic of Germany combining the experiences in Giessen and Hannover on over 50,000 pregnant women, about evenly distributed among both centers. Published and known forthcoming data from other low incidence populations, particularly of European countries, are reviewed briefly. The conclusion is reached that general screening could effectively be instituted and in the final result should also be cost-beneficial.

Cholinesterase evaluation in the prenatal diagnosis of open neural tube defects

Alpha-fetoprotein (AFP) and cholinesterase levels in amniotic fluid were determined and the efficiency of these laboratory tests in the prenatal diagnosis of neural tube defects was examined. Using the AFP test with cut-off levels correlated to gestational age, we have detected 8 cases of neural tube defects and one case of abdominal wall defect in about 1,200 pregnancies; false-negative values were absent. Acetylcholinesterase (AChE) and butyrylcholinesterase activities were measured and the electrophoretic pattern of AChE was examined in 100 amniotic fluid samples. The diagnosis of neural tube defects was always confirmed. There were no diagnostic problems due to blood-contaminated amniotic fluid samples. The results obtained using different quantitative methods for the determination of cholinesterase activity, as well as the potential use of these tests in routine examinations, are discussed.

Quantitative determination of acetylcholinesterase by enzyme antigen immunoassay: methodological aspects and clinical use

We here describe the optimization of an immunochemical measuring method for acetylcholinesterase (AChE) found in different human body fluids. The principle is the binding of a polyclonal antibody to a solid support (microtitre plate), followed by quantitation of the enzymatic active antigen, by its own enzymatic activity. The test is mainly thought as a diagnostic tool for the prenatal detection of neural tube defects (NTD). The assay is optimized with respect to antibodies and a number of physical parameters. The test is accurate and reliable, and it yields quantitative results. Further we show it to give neither false positive nor false negative values in the prediction of NTD. The assay also performs well on other sample-materials. We suggest that the test will be routinely used alongside amniotic alpha-fetoprotein (AFP) determinations to ensure the correct prenatal diagnosis of NTD.

Prenatal assessment of anterior abdominal wall defects and their prognosis

Eighty-eight cases of abdominal wall defect with and without other lesions were ascertained by reviewing all labour room records in the West of Scotland, all surgical admissions to the Royal Hospital for Sick Children, Yorkhill, and all post mortems at Royal Hospital for Sick Children between 1978 and 1981. The affected cases comprised 39 terminations of pregnancy (17 of anterior abdominal wall defect without neural tube defect), 20 spontaneous stillbirths and 29 livebirths. All 10 cases of body stalk anomaly, 37.5 per cent of 16 gastroschisis cases and 53 per cent of 62 exomphalos cases had additional severe abnormalities. Abnormal karyotypes were present in seven out of 19 exomphalos cases but all karyotypes from 10 gastroschisis and 6 body stalk anomaly cases were normal. No correlation was found between the maternal serum AFP levels, the amniotic AFP levels and acetylcholinesterase results and the size of the lesion. It is proposed that anterior abdominal wall defects detected prenatally should have chromosome analysis and careful ultrasound to exclude associated severe anomalies before coming to a decision about termination. This policy was implemented in six pregnancies complicated by fetal gastroschisis without severe associated anomalies which were identified in the second trimester and continued to term. Immediate surgical repair was achieved in each case, although two of the infants succumbed from later complications of gastroschisis closure and one from respiratory distress syndrome. The remaining three infants made a satisfactory recovery.

Glial fibrillary acidic protein in amniotic fluids from pregnancies with fetal neural tube defects

The glial fibrillary acidic protein (GFAP) is the subunit protein of intermediate filaments in astrocytes and closely related cell types. By means of an enzyme immunoassay we have determined the concentration of GFAP in amniotic fluids from normal pregnancies and from pregnancies complicated by various fetal malformations. The group of 20 cases of fetal anencephaly had a significantly higher mean amniotic fluid GFAP concentration (115 micrograms/l +/- 133.6 (S.D.), range 6-378 micrograms/l) than the control group of 117 normal pregnancies (13 micrograms/l +/- 5.5 (S.D.), range 0-31 micrograms/l), (P less than 0.001). Two cases of fetal encephalocele likewise had very high amniotic fluid GFAP concentrations. None of the other cases of fetal malformations investigated, including 12 cases of spina bifida, had increased amniotic fluid GFAP concentrations. We conclude that determination of the amniotic fluid GFAP concentration may give additional information in the prenatal diagnosis of fetal nervous system malformations.