[Unusual behavior of serum markers in risk evaluation for trisomy 21]

Screening of Down syndrome using serum markers is based on statistic risk determination calculated from the results of markers. An increased risk of fetal Down syndrome is associated with high hCG levels and low AFP levels in maternal serum. In the daily practice, the use of these two markers also leads to observation of different analytical patterns. We reviewed these patterns according to published data and our own experience. Some patterns are well documented (neural tube defects or trisomy 18) some of them remain unexplored. Numerous difficulties are encountered in the clinical use of these markers patterns: lack of consensus for their analytical definition, problems in interpretation, lack of regular dispositions.

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.

[Electrophoresis of cholinesterases of the cerebrospinal fluid in the Guillain-Barré syndrome]

Polyacrylamide gel electrophoresis of cholinesterase from cerebrospinal fluid was performed in 22 patients with Guillain-Barré syndrome. Fifteen of these patients had an abnormal cerebrospinal fluid with emergence of a second electrophoretic migration band corresponding to non-specific cholinesterase. Among 182 patients with a variety of diseases who served as controls, only one presented with this abnormality. From these data the sensitivity and specificity of cerebrospinal fluid cholinesterase electrophoresis were calculated at 68 and 99 percent respectively. The second migration band seems to appear early in the course of the disease and disappears when the patient is cured. Moreover, the occurrence of this band is correlated with the severity of the condition, as shown by a greater number of patients under artificial ventilation and by a longer stay in intensive care unit. Cerebrospinal fluid electrophoresis could be used as a prognosis factor.

[Results of pregnancies characterized by a decrease in the level of alpha-fetoprotein in the maternal blood]

Pregnancy outcome was followed in 123 women showing maternal serum alpha-fetoprotein, less than or equal to 0.50 MOM. In 28 cases AFP was secondarily considered as normal either after ultrasonography and correction of gestation age or after a second sample normal result. In 95 cases AFP level was confirmed lowered; perinatal outcome was normal in 70 cases and abnormal in 25. Among these 25 cases, 3 autosomal trisomies occurred, 2 trisomies 18 and 1 trisomy 21; in the 22 other cases, we observed antepartum risk factors (10 cases with impending premature labor or premature labor, 9 cases with chronic hypertension, 2 cases with Ag HBs hepatitis and 1 case with diabetes).

[Alpha-fetoprotein and trisomy 21]

In 31 affected pregnancies with Down syndrome, the median maternal serum alpha-fetoprotein value was lower than normal, 0.76 MoM, and median amniotic fluid value was quite normal, 0.98 MoM. Selecting an arbitrary cutoff-point of 0.5 MoM, 4.1 percent of normal gestations show values less than 0.5 MoM. Authors discuss problems about screening for fetal Down's syndrome by measuring maternal serum AFP levels.

[Biochemical markers of neural tube closure defects during the second half of pregnancy]

Increasing number of amniocentesis done during the second half of gestation with indication "signe d'appel" made necessary for authors to study amniotic fluid markers in late pregnancy. Normal evolution curve must be established with samples obtained after 20 weeks gestation. Study reveals more false-negative results with AFP than before 20 weeks. AChE remains constantly positive in cases with NTD, band aspect being specific. For other malformations, AChE positivity seems inconstant, with a different aspect. Some normal gestation cases can be associated with faint AChE band.

[Unusual increase in amniotic fluid alpha fetoprotein and trisomy 13]

From 10 observations of trisomy 13, 3 presented an elevated amniotic fluid alpha-fetoprotein level considered as unusual in 2 cases, superior to cut-off level in the other case. Macroscopic examination of the three fetus could not reveal a cause of AFP elevation, neural tube defect or abdominal wall defect. The authors discuss the role of an undetected abnormality such as minor scalp defect with very thin membrane and for one case false-negative result of Kleihauer test.

[Prenatal diagnosis of 4 cases of spina bifida in mothers treated with valproate]

The potential risk of spina bifida (SB) after fetal exposure to Valproate led the authors to apply the following protocol: in case of first trimester exposure to Valproate, prenatal diagnosis is offered and consists of both amniotic fluid examination and fetal ultrasound to detect open spina bifida. In the period 1983 to June, 1986, this program allowed early detection of three cases of SB and pregnancy termination. Another case escaped the programme: neural tube defect was detected lately and the child had to be operated upon. These four cases of SB underline the necessity of prenatal diagnosis with combined use and confrontation of ultrasound examination and biochemical amniotic fluid tests.

[Contribution of amniocentesis to prenatal screening of neural tube closing defects: evaluation of 10 years of a center's experience]

The authors report retrospective data on analysis of amniotic fluid DFTN markers (AFP and AChE) from 306 cases. Data were obtained from 261 amniocentesis done because there was a recurrence risk of DFTN and from 45 amniocentesis done because an anomaly as DFTN was diagnosed with ultrasonography. Results first show that the risk of recurrence is 3.03% in Rhône-Alpes area. In utero exposure to valproate appears as new indication for amniocentesis, in view of the possible association between Spina-Bifida and prenatal-valproate exposure (1/8 in the study). In contrast to anencephaly, Spina Bifida can be difficult to diagnose with ultrasonography before 20 weeks and require amniocentesis with AFP and AChE study.

[Amniotic fluid acetylcholinesterase and prenatal diagnosis of neural tube defects. II. Qualitative test]

The qualitative acetylcholinesterase (AChE) test has been used in conjunction with alpha-fetoprotein (AFP) assay on 255 amniotic fluid samples: 191 from normal pregnancies, 44 from abnormal pregnancies (foetal anomalies or intrauterine death). In all cases of normal amniotic fluid obtained before 25 weeks, gel revealed a single major band of non specific cholinesterase, even in fluids contaminated by maternal of foetal blood, whereas 5 fluids contaminated by foetal blood were false positive on AFP. In 8 normal specimens with clear aspect, obtained after 25 weeks, gel revealed a second (AChE) faint band, inhibited by BW 284 C 51. That result shows the risk of false-positive for samples obtained in late pregnancy. All 20 cases of neural tube defect gave a characteristic AChE band: large and intense band. In 9 cases of abdominal wall defect, 3 presented an AChE faint band, just as 2 cases of atresia and 2 cases of hydronephrosis. Negative AChE results were found un 1 case of congenital nephrosis, 3 cases of hydrocephaly and 1 case of teratoma. The main value of qualitative AChE test seems today in diagnosing neural tube defects with a greater sensibility and in classifying bloody fluids in which the AFP is at or above the cut-off level.

[Acetylcholinesterase of amniotic fluid: application to prenatal diagnosis of neural tube closing defects. I. Quantitative tests]

Acetylcholinesterase (AChE) in amniotic fluid from 165 normal pregnancies and 38 abnormal pregnancies was measured, using a direct assay of AChE activity after inhibition of ChnS with ethopropozine ("Lysivane"). Samples from normal pregnancies of 16-24 weeks gestation have a mean AChE activity of 2,7 U/1 and those obtained at 26-40 weeks have a mean level of 0,6 U/l. Contamination of amniotic fluid with fetal or maternal blood was observed to elevate AChE activity leading to uninterpretable results. Assays in artificial mixtures of amniotic fluid with maternal or fetal blood confirm the risk related to added erythrocyte number. Higher mean AChE activity, 8 U/l, was observed in association with open NTD, but in 7 cases the level was as in normal pregnancy. Elevated levels of AChE were found in association with Turner's syndrome (1) and intra uterine death (2); no increase was observed in 7 cases of omphalocele or laparoschisis, in 6 cases of atresia and 2 cases of hydrocephaly. In practice frequent occurence of bloody samples, specially from abnormal pregnancies, limits application of the test for antenatal open NTD diagnosis. This test appears as and useful preliminary stage providing informations for realization and interpretation of gel electrophoresis of cholinesterases.

[Acetylcholinesterase: an additional test for diagnosis of fetal malformations]

From an observation of in utero suspected myelomeningocele, the authors underline interest of pattern of cholinesterases using acrylamide gel electrophoresis. The AChE isoenzyme band appears in some fetal malformations, particularly NTD. This biochemical test is considered as complementary of the AF alpha-fetoprotein assay.