Acetylcholinesterase in human amniotic fluid: An index of fetal neural development?

Evaluation of the potential effect of transgenic rice expressing Cry1Ab on the hematology and enzyme activity in organs of female Swiss rats

To assess the safety of transgenic rice expressing Cry1Ab protein to vertebrates, the effect of Cry1Ab rice on broad health indicators in blood and various organs of Swiss rats were analyzed. The 30 and 90 day safety studies of Cry1Ab rice on female Swiss rats revealed that Cry1Ab rice had no significant effect on the several elements of blood lymph including hemogram, calcium ion concentration and apoptosis rate of lymphocytes, indicating that Cry1Ab protein could not affect the blood lymph of Swiss rat. Similarly, Cry1Ab rice had no effect on enzyme activities in a variety of organs of Swiss rat. However, Cry1Ab rice did have significant effects on the blood biochemistry indexes including urea, triglyceride (TG), glutamic oxalacetic transaminase (AST) and alkaline phosphatase (ALP) after the rats were fed with Cry1Ab rice for 30 days, but not after 90 days, indicating that Cry1Ab protein may influence blood metabolism for a short duration. Quantitative real-time PCR (qPCR) analysis of the 6 genes encoding enzymes responsible for the major detoxification functions of liver revealed that Cry1Ab rice exerted no influences on the levels of these transcripts in liver of Swiss rat, indicating that significant differences registered in part of the blood biochemical parameters in the 30 day study might result from other untested organs or tissues in response to the stress of exogenous Cry1Ab protein. The results suggest that Cry1Ab protein has no significant long-term (90 day) effects on female Swiss rat.

Acetylcholinesterase in Hirschsprung's disease

The association between the congenital absence of colonic ganglion cells and an increased acetylcholinesterase (AChE) expression in the affected tissue is of diagnostic importance in Hirschsprung's disease (HSCR). Investigation of AChE's function in development may also help unravel some of the complex pathophysiology in HSCR. Normal nerves do not stain for AChE, but increased AChE expression is associated with the hypertrophied extrinsic nerve fibres of the aganglionic segment in HSCR. Although a high degree of histochemical diagnostic accuracy exists, results are not always uniform, and false positives and false negatives are reported. False negative results are primarily related to age, and an absence of AChE reaction does not exclude HSCR in neonates within the first 3 weeks after birth. AChE staining results may lack uniformity, resulting in a number of technical modifications that have been made to improve standardization of AChE staining. At least two distinct histological patterns are described, types A and B. The interpretation of increased AChE staining patterns in ganglionated bowel at the time of surgical pull-through remains a problem in patients with HSCR. The development of rapid staining techniques has helped to identify normal ganglionated bowel with greater certainty. The presence of fine AChE neurofibrils in the ganglionated segment has contributed to the debate surrounding intestinal neuronal dysplasia. Quantitative assay of cholinesterase activity confirms the pattern of histochemical staining. AChE is particularly increased in relation to butrylcholinesterase, with one molecular form, the G4 tetrameric form, predominating. It is likely that the raised levels of AChE in aganglionic tissue are the transcriptional consequence of the abnormalities in signalling molecules that characterize HSCR. Evidence suggests that this AChE is functioning in a nonenzymatic capacity to promote cell adhesion and differentiation and that the hypertrophied nerves and neurofibrils may be the result of this increased AChE expression.

Tissue distribution of human acetylcholinesterase and butyrylcholinesterase messenger RNA

Cholinesterase inhibitors occur naturally in the calabar bean (eserine), green potatoes (solanine), insect-resistant crab apples, the coca plant (cocaine) and snake venom (fasciculin). There are also synthetic cholinesterase inhibitors, for example man-made insecticides. These inhibitors inactivate acetylcholinesterase and butyrylcholinesterase as well as other targets. From a study of the tissue distribution of acetylcholinesterase and butyrylcholinesterase mRNA by Northern blot analysis, we have found the highest levels of butyrylcholinesterase mRNA in the liver and lungs, tissues known as the principal detoxication sites of the human body. These results indicate that butyrylcholinesterase may be a first line of defense against poisons that are eaten or inhaled.

False-positive amniotic fluid acetylcholinesterase analysis in the third trimester

Thirty-two third-trimester amniotic fluid samples were studied according to the indication for amniocentesis, result of acetylcholinesterase (AChE) analysis, and outcome, in order to address the issue of the effectiveness of AChE testing late in gestation. The results indicate that third-trimester AChE analysis is less effective than second trimester in distinguishing open neural tube defects (ONTDs) and ventral wall defects (VWDs) from other abnormalities. False-positive results occurred in cases of isolated hydrocephaly (four of seven cases), polyhydramnios, and intrauterine growth retardation (IUGR). Caution is recommended in interpreting third-trimester AChE tests, particularly when neither an ONTD nor a VWD is observed by ultrasound.

Association of generalized dystrophic epidermolysis bullosa with positive acetylcholinesterase and markedly elevated maternal serum and amniotic fluid alpha-fetoprotein

A case of fatal generalized dystrophic epidermolysis bullosa is described in a prematurely born female whose mother had strikingly elevated mid-trimester serum and amniotic fluid alpha-fetoprotein concentrations, a positive amniotic fluid acetylcholinesterase band, and negative serial ultrasound studies. This case lends further support to an association between autosomal recessive generalized dystrophic epidermolysis bullosa and increased levels of alpha-fetoprotein, positive amniotic fluid acetylcholinesterase, and normal ultrasound findings.

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.

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.

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: implications of an inconclusive result

The implications of an "inconclusive" acetylcholinesterase test (a faint but true band) in amniotic fluid were studied over a 2 1/2-year period in our laboratory. One thousand one hundred fifty-four amniotic fluid samples were tested for acetylcholinesterase and alpha-fetoprotein; the rate of an inconclusive acetylcholinesterase result was 3.3% (38 of 1154). Fourteen such results were found in patients with a high amniotic fluid alpha-fetoprotein level (23.3%), and 24 results were associated with normal amniotic fluid alpha-fetoprotein levels (2.19%). The rates of congenital fetal malformation associated with an inconclusive acetylcholinesterase result in the two groups were 57.14% and 37.5%, respectively. In amniotic fluid samples obtained before 15 weeks' gestation, there was a higher rate of inconclusive acetylcholinesterase tests (9.29%), but a lower percentage of malformed fetuses were found compared with later in pregnancy (2.46% and 56%, respectively). Thus we suggest the terminology "equivocal" for early specimens and "suspicious" for later specimens. If obtained in early second trimester and the ultrasound scan is normal, such findings implicate the need for a careful search for fetal malformations. A positive pregnancy outcome may be expected in most cases.

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.

The association of congenital skin disorders with acetylcholinesterase in amniotic fluid

We describe a fetus with epidermolysis bullosa dystrophica and a fetus with aplasia cutis congenita who were normal by careful ultrasound examination but whose midtrimester amniotic fluids exhibited elevated concentrations of alpha-fetoprotein and presence of acetylcholinesterase. These cases show that serious fetal skin pathology can be a source of amniotic fluid acetylcholinesterase and elevated alpha-fetoprotein concentration and should be considered as part of the differential diagnosis of these amniotic fluid findings.

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.

Routine amniotic fluid alphafetoprotein assay: experience with 40,000 pregnancies

Of 40,000 initial amniotic fluid samples, 0.7% had an alphafetoprotein (AFP) level greater than or equal to +3 standard deviations above the mean. The risk of an open neural tube defect (NTD) or other serious fetal abnormality was 61% when AFP levels measured greater than or equal to +3 and 87% for levels greater than or equal to 5 standard deviations. If the acetylcholinesterase (AChE) was positive, this risk was 84% and 95% for AFP levels of greater than or equal to +3 and greater than or equal to +5 SD, respectively, and 29% and 62% for the same levels if the AChE was negative. If the second amniocentesis AFP was also greater than or equal to +3, the risk of an abnormality was 96%. In this series, there were 93 open neural tube defects, and all were identified. The true false-positive rate was 1 per 13,000 of the cases screened. The recurrence risk for an NTD was 1.8%, and the incidence of NTDs in women having amniocentesis only for maternal age was 1.5 per 1,000.

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)

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.

Predictive value of amniotic acetylcholinesterase analysis in the diagnosis of fetal abnormality in 3700 pregnancies

The value of acetylcholinesterase (AChE) analysis as an adjunctive test to amniotic alpha fetoprotein (amAFP) for the diagnosis of fetal abnormality has been investigated in a series of 3785 amniotic fluid samples. Quantitative analysis of AChE performed retrospectively on a selected group of 541 amniotic fluid samples failed to discriminate between normal and open neural tube defect pregnancies. Qualitative analysis of AChE by polyacrylamide gel (PAG) electrophoresis in the same series of 541 fluids correctly identified 251 of the 255 pregnancies with open neural tube defect and 29 of the 31 pregnancies with false positive amAFP results. The failure of the test to diagnose 4 cases of open neural tube defect was probably attributable to the age and condition of the stored AF samples. Routine diagnostic testing of AChE isoenzymes in a further 3244 AF samples successfully identified all 170 cases of open neural tube defect and 20 cases with other fetal defects. Thirteen fluids gave false positive AChE results (0.4 per cent) compared to 59 of the series in which there were false positive amAFP results (1.8 per cent). Six of the 13 false positive AChE cases had AChE bands of low intensity which would not be regarded as diagnostic of fetal abnormality, and in five the AChE band may have been the result of significant blood contamination. False positive AChE results contributed to the decision to abort three apparently normal fetuses, but a normal AChE result undoubtedly helped to save a number of pregnancies with false positive amAFP results. Our experience suggests that repeating the amniocentesis may help in resolving the rare diagnostic difficulty of a positive AChE result with or without an elevated amAFP in the absence of ultrasound evidence of fetal abnormality, particularly where there is blood contamination of the amniotic fluid sample.

A prospective study of amniotic fluid cholinesterases: comparison of quantitative and qualitative methods for the detection of open neural tube defects

The value of quantitative and qualitative methods of cholinesterase (ChE) analysis in the detection of open neural tube defect (NTD) has been assessed in a prospective survey of 1495 mid-trimester amniotic fluids. Using a quantitative method the mean ChE values were much lower in fluids from pregnancies of normal outcome but it was not possible to discriminate these fluids completely from those associated with NTD pregnancies, particularly when the specimens were contaminated with blood. Similarly, measurement of acetylcholinesterase (AChE) activity alone by three different methods also failed to eliminate the overlap between the two groups. In contrast, polyacrylamide gel electrophoresis revealed only a single band of ChE activity in 1408 out of 1410 fluids from pregnancies with a normal outcome whilst amniotic fluids from all 60 cases of open NTD, 6 out of 7 cases of exomphalos and 3 out of 4 cases of intra-uterine death gave the characteristic second faster-running AChE band. A qualitative gel method which requires the same amount of ChE activity to be loaded from each amniotic fluid is an effective method for pre-natal diagnosis of NTDs.

Routine amniotic fluid alpha-fetoprotein measurement in 34,000 pregnancies

Of 34,000 initial amniotic fluid samples, 0.7% had an alpha-fetoprotein level greater than or equal to +3 SD above the mean. The risk of an open neural tube defect or other serious fetal abnormality was 60% when alpha-fetoprotein levels measured greater than or equal to +3 and 86% for levels greater than or equal to +5 SD. In this series there were 72 open neural tube defects, and all were identified. The true false positive rate was 0.9 per 10,000 cases screened.

A clinical approach to the use of predictive values in the prenatal diagnosis of neural tube defects

The rationale of calculating predictive values to interpret the amniotic fluid alpha-fetoprotein (AFP) test has been examined and applied to amniotic fluid AFP testing from one Canadian center. Such predictive value ccalculations may be misleading if they fail to make use of the actual magnitude of the test result or the results of other investigations. The alculation of predictive values has thus been extended to take into account magnitude of the test results, the clinical history, and the results of other investigations. The interpretation of an abnormal amniotic fluid AFP test that is followed by a normal result of a careful ultrasound scan of the fetal back is that there is a 54.5% chance that the fetus has spina bifida if there is a previous history of spina bifida. There is a 12.5% chance if there is a negative family history. These calculations lead to informed genetic counseling and rational decision making with regard to the continuation of the pregnancy.

Identification of acetylcholinesterase and cholinesterase in amniotic fluid by immune absorption technique

A method for immunological detection of acetylcholinesterase (AChE) and cholinesterase (ChE) in amniotic fluid is described. By addition of a small amount of antihuman-erythrocyte membrane antibody or anti-pseudocholinesterase antibody to the sample before electrophoresis the two esterase bands on polyacrylamide gel (PAG) can be absorbed away. Similar staining results can also be obtained by specific inhibition of the two esterases with either BW 284C51 (AChE inhibitor) or Lysivane (ChE inhibitor). In cases with a faint AChE band and in cases with blood contamination the immune absorption technique makes interpretation easier. Nearly identical staining results have been obtained by the immune absorption technique and the inhibition technique in the following samples with an AChE band: 34 samples from pregnancies with severe fetal malformation or intrauterine death (2 cases), 4 fetal serum samples, 4 samples of cerebrospinal fluid, 4 samples of fetal erythrolysate and 4 samples of adult erythrolysate. It can be concluded that an antibody prepared against erythrocyte AChE cross-reacts with AChE in cerebrospinal fluid, and that this antibody can be used for demonstration of AChE in amniotic fluid.

Prenatal diagnosis of neural tube defects: experiences with acetylcholinesterase gel electrophoresis

We assessed the qualitative test for AChE in addition to AFP for the diagnosis of NTD in 420 AF samples selected from 16,000 second trimester amniocenteses. Three-hundred and thirty were from normal and ninety from abnormal pregnancies. There were three false positives by this test, two from stored samples containing fetal blood and one from a clear specimen; all had normal outcomes and two had had abnormal AFPs. Forty-seven of forty-seven NTDs were positive by AChE and included 26 cases of anencephaly, 16OSBs, and 5 encephaloceles. In addition, about half of the cases of omphalocele, fetal demise, cystic hygroma, and hydrops gave positive results. One case of congenital nephrosis was negative. We conclude that AChE gel electrophoresis is a useful adjunctive test when AFP levels measure +3 SD above the mean. Although no false negative occurred in this series identified by elevated AFP or increased risk for NTDs, the number in unselected pregnancies is not known.

Improved discrimination in the detection of neural tube defects: five biochemical tests compared

Five biochemical tests, which have been proposed as possible adjuncts to the measurement of amniotic fluid alphafetoprotein for the identification of neural tube defects, have been measured in 49 normal and 46 neural tube defect affected pregnancies. One test, the alphafetoprotein component non-reactive with concanavalin A, was ineffective in differentiating normal and abnormal. The remaining four procedures, the activity of acetyl and total cholinesterase, the concentration of alpha 2 macroglobulin and the electrophoretic identification of acetyl cholinesterase effectively separated the normal and abnormal populations. The relative merits of these four latter tests in the evaluation of false positive and false negative amniotic fluid alphafetoprotein results, as well as in liquor samples with high alphafetoprotein levels associated with abnormalities not of neural origin, are discussed.

Acetylcholinesterase in neural tube defects: a model using chick embryo amniotic fluid

Acetylcholinesterase was measured in amniotic fluid from normal chick embryos and embryos with neural tube defects. Neural tube defects were induced in the chick embryos by three procedures, removal of albumen, mechanical disruption of the closed neural tube or injection of tetanus toxin. The concentration of acetylcholinesterase in amniotic fluid from untreated normal embryos changed throughout the period examined (5-14 days incubation) but was stable at 0.5 U1(-1) over the time period 6-11 days. Amniotic fluid taken from treated embryos with neural tube defects at 8 days always contained a higher concentration of acetylcholinesterase than fluid from sham operated but otherwise normal embryos, mean 40.9 U1(-1), S.E.M. = 10. U1(-1), versus 1.0 U1(-1), S.E.M. = 0.2 U1(-1). The range of values (6.1-393 U1(-1)) was clearly separated from the normal values, range 0.0-5.5 U1(-1). In 13 cases with developmental abnormalities other than neural tube defects, the concentration of acetylcholinesterase was elevated in only one. Two different forms of acetylcholinesterase, as shown by gel electrophoresis, were present in fluid form both normal and defective embryos. These forms were also present in blood plasma, cerebrospinal fluid and in the high speed supernatant from brain extracts, the latter tissue contained an additional form of greater electrophoretic mobility. After irreversible inhibition, enzyme activity in amniotic fluid recovered slowly; only half the control value was reached by 140 h compared with complete recovery in the tissues of the embryo within 19 h. Histochemical staining for acetylcholinesterase showed that the spinal cord in the region of the lesion contained high concentrations of the enzyme. The possible sources of acetylcholinesterase in amniotic fluid are discussed. This chicken model of neural tube defects provides support for the use of acetylcholinesterase tests in the detection of neural tube defects clinically, and provides a model for experimentation with this system.

Gel electrophoresis of maternal and fetal serum cholinesterases from normal pregnancies and of those affected by neural tube defects

The cholinesterase isozymes of maternal and fetal sera from normal pregnancies and those in which the fetus had a neural tube defect were studied using flat-bed vertical polyacrylamide gel electrophoresis. Normal maternal and fetal sera had multiple bands of cholinesterase activity, including the two bands in the position of those found in amniotic fluid from NTD pregnancies. The one difference between maternal and fetal sera was that the faster of these two "amniotic fluid bands" was acetylcholinesterase in fetal serum, as in the neural tube defect amniotic fluids, but non-specific cholinesterase in maternal serum. In artificial mixtures this difference could be used to differentiate between maternal and fetal blood-contamination of amniotic fluids, but in samples naturally contaminated at amniocentesis this test did not always agree with the Kleihauer findings. Both maternal and fetal sera had additional weak acetylcholinesterase activity in the most anodally migrating enzyme bands, but all other enzyme activity was non-specific cholinesterase. No difference was observed in the isozymes of fetal serum from normal fetuses and those with neural tube defects, or of maternal serum from normal and neural tube defect pregnancies.

Amniotic fluid acetylcholinesterase: a retrospective and prospective study of the qualitative method

After retrospective evaluation with stored samples, the qualitative acetylcholinesterase (AChE) test has been used prospectively in conjunction with alpha-fetoprotein (AFP) assay on 986 amniotic fluid specimens received in this laboratory during 1980. The main value of AChE is in classifying fluids in which the AFP level is near the threshold between normal and abnormal. Among abnormal pregnancies with raised AFP levels, neural-tube defects can generally be distinguished from other abnormalities by careful appraisal of the AChE gel pattern, but confirmation of these other fetal abnormalities may require high resolution diagnostic ultrasonography and perhaps fetoscopy. Neural-tube defects with false negative AFP levels can be detected by AChE, but AChE gives occasional false positives so that it cannot be relied on in isolation for the diagnosis of neural-tube defects.

Prenatal diagnosis--a compilation of diagnosed conditions

This article provides physicians with an up-to-date listing of 182 fetal conditions diagnosed prenatally. This information is presented in two key tables: the first an alphabetical listing of the conditions and the second a grouping of them according to disease categories. The latter table also presents the technique(s) used to establish the diagnosis, as well as pertinent references. Chromosomal abnormalities, diagnosed from amniotic fluid cell karyotypes, have not been individually tabulated in either table. Current techniques utilized for prenatal diagnosis are presented (see Comment).

Acetylcholinesterase and butyrylcholinesterase measurement in the pre-natal detection of neural tube defects and other fetal malformations

Acetylcholinesterase activity in amniotic fluid was measured at 30 degree C by a reaction rate method employing acetyl-beta-methyl thiocholine as substrate and ethopropazine as a selective inhibitor of butyrylcholinesterase. This assay proved more specific than previously reported methods. Activity was greater in five cases of anencephaly (4.8-9.7 U/l) and nine cases of spinal bifida (5.1-8.6 U/l) than in 50 pregnancies with normal outcome (mean activity 2.0 +/- 0.9 (S.D.) U/l). There was no overlap between results from normal and neural-tube-defect groups, and the results showed no significant correlation with gestational age. Butyrylcholinesterase activity in amniotic fluid was measured using butyrylthiocholine as substrate. In accordance with previous reports, levels were elevated in pregnancies affected by neural tube defects. The ratio butyrylcholinesterase/acetylcholinesterase activity showed similar values for anencephalic, spina bifida and normal pregnancies; however, the two cases of exomphalos investigated could be clearly distinguished from all other groups on this basis.

Particulate acetylcholinesterase in amniotic fluid and its implications for neural tube defect screening

Acetylcholinesterase activity in mid-trimester amniotic fluid has been determined by a quantitative spectrophotometric method and a qualitative electrophoretic technique in a limited (76 samples) retrospective study. Differential centrifugation studies on amniotic fluid from normal pregnancies demonstrated the presence of particle-associated acetylcholinesterase sedimenting only at relatively high centrifugal forces. It is postulated that this particle-associated activity was a contributory factor to an observed false-positive incidence of 6.6% when quantitative acetylcholinesterase measurement was used to discriminate between normal pregnancies and those associated with neural tube defects. Discrimination on the basis of electrophoretic analysis of acetylcholinesterase resulted in no misclassification of pregnancies. Particulate acetylcholinesterase would not be expected to influence the interpretation of the electrophoretic pattern due to its size-related exclusion from gel pores. The implication of these observations in the accurate prenatal diagnosis of neural tube defects is discussed.

Prenatal diagnosis of neural tube defects: predictive value of AF-AFP in a low-risk population

Amniotic fluid alpha-fetoprotein (AF-AFP) determinations were performed on 1,215 women who were at low risk for fetal neural tube defects and who were undergoing mid-trimester amniocentesis for cytogenetic indications, primarily age-related aneuploidy. Maternal sera obtained before amniocentesis and amniotic fluids were assayed in duplicate for alpha-fetoprotein by radioimmunoassay. Of the 1,215 low-risk women, eight (0.7%) had significant elevations of AF-AFP (greater than or equal to +5 SD). In none of the cases was the elevation associated with a fetal neural tube defect. Two cases with elevated AF-AFP were associated with chromosome aberrations; one with impending fetal demise; one with fetal blood contamination; and one case was due to a laboratory error. In one case, no source for the elevated AFP was found, and a normal infant was delivered at term. In the final two cases, the cause of the elevated AF-AFP was a fetal abdominal wall defect (one gastroschisis and one omphalocele). The predictive value of an elevated AFP varies with the population screened, and is reduced by routine ultrasonography before amniocentesis, which at least identifies anencephaly. In a low-risk population, an elevated AF-AFP is most often not associated with a fetal neural tube defect. Because of the low predictive value and the nonspecificity of AF-AFP, genetic counselors should reconsider the recommendation of routine AF-AFP in low-risk maternal populations.

Polyacrylamide gel electrophoresis of amniotic fluid cholinesterases: a good prenatal test for neural tube defects

The qualitative assay of the cholinesterases (ChE) in amniotic fluid on polyacrylamide gel gave a single major band (cholinesterase) in all samples from normal pregnancies, and two major bands (cholinesterase and acetylcholinesterase) in all cases from fetuses with open neural tube defects. Five fluids which were true false positive on alpha-fetoprotein (AFP) assay (elevated AFP in a clear fluid but normal fetus) had a single band, and two fluids which were false negative on AFP testing (normal AFP but spina bifida fetus) had two bands. The second 'diagnostic' ChE band sometimes occurred, together with other extra bands, in some fluids which were very severely contaminated by maternal or fetal blood, but in four of six fluids from normal fetuses where fetal blood staining was sufficient to cause the AFP to be elevated, there was only one ChE band. It is suggested that the qualitative assay of ChE should be performed in addition to AFP in the prenatal diagnosis of neural tube defects.

Prenatal diagnosis of neural tube defects. V. The value of amniotic fluid cholinesterase studies

Total cholinesterase activity in amniotic fluid obtained from 150 fetuses was measured. Elevated values were found in 94% of samples from fetuses known to have neural tube defects (spina bifida, anencephaly) when compared to nonbloody samples from normal fetuses. Contamination of amniotic fluid with blood was observed to elevate total cholinesterase activity in some, but not all, such specimens. Total cholinesterase activity did not vary with gestational age between 15 and 24 weeks. These data were compared to our large alpha-fetoprotein (AFP) assay experience used for the prenatal detection of neural tube defects. We concluded that the assay of total cholinesterase activity in amniotic fluid could be a useful adjunct to the AFP assay, especially in those samples contaminated with blood.

Amniotic fluid acetylcholinesterase and prenatal diagnosis

Raised specific acetylcholinesterase (AChE) activity in amniotic fluid was consistently found to be associated with fetal intrauterine death and neural tube defects, but in just under half of the samples from pregnancies with spina bifida, the increase was marginal. Elevated AChE levels were occasionally found in fluid samples contaminated by maternal blood, and in nearly half of the samples which were a brown or yellow-brown colour but where there was a normal fetus. Nine fluids, five of which were contaminated with fetal blood, had a false positive result on alpha-fetoprotein (AFP) assay (elevated AFP levels and a normal fetus), but showed normal AChE activities. It is suggested that AChE estimation might be useful in prenatal diagnosis as a second test for those fluids which have an elevated AFP level.