Amniotic fluid disaccharidases in the prenatal detection of cystic fibrosis

The intestinal damage induced by lipid soluble meconium subfraction is profound compared to the intestinal damage induced by water soluble meconium subfraction

BACKGROUND

It is unclear which substances in meconium are responsible for intestinal damage in gastroschisis. An experimental study was designed to investigate the effects of the lipid or water soluble subfractions of meconium on the intestines of gastroschisis in a chick model.

METHODS

Meconium was pooled, homogenated, rota-evaporated dry and diluted. Meconium subfractions were obtained from water soluble and lipid soluble extracts of the meconium. Five days old fertilized chick embryos were used and divided into 5 groups: control, sham, water soluble meconium subfraction, lipid soluble meconium subfraction and whole meconium. All embryos were extirpated on the 18days and the intestines were harvested for histopathological examination. Serosal thickness was measured under light microscopy.

RESULTS

Serosal thickness of the meconium (36.36±2.8μm), the water soluble meconium (14.15±0.93μm) and the lipid soluble meconium (23.88±1.69μm) subfractions groups were significantly increased compared with the control (7.47±0.68μm) and the sham (7.48±0.71μm) groups (p<0.001). Serosal thickness of the lipid soluble meconium subfraction group was significantly increased compared with the water soluble meconium subfraction group (p<0.001). Serosal thickness of the meconium group was significantly increased compared to both the water and the lipid soluble meconium subfraction groups (p<0.001).

CONCLUSION

Lipid soluble meconium subfraction induces more intestinal damage compared to water soluble meconium subfraction.

Induction of fetal diuresis with intraamniotic furosemide increases the clearance of intraamniotic substances: An alternative therapy aimed at reducing intraamniotic meconium concentration

BACKGROUND/PURPOSE

Contact with amniotic fluid (AF) causes intestinal damage in gastroschisis. Intraamniotic meconium has been shown to be responsible for intestinal damage, and occurrence of this damage has been shown to depend on the concentration of intraamniotic meconium. When intraamniotic meconium concentration is lowered below threshold level by exchanging AF with saline in gastroschisis, intestinal damage can be prevented. Theoretically, induction of fetal diuresis with intraamniotic furosemide may increase AF volume and fetal swallowing rate, thus, increase absorption of AF by intestines; therefore, the clearance of meconium from the AF may increase. An experimental study was planned to investigate the effects of intraamniotic diuretic injection on the clearance of intraamniotic substances.

METHODS

Pregnant rabbits on the 23rd to 25th gestational day were divided into 2 groups as furosemide and control. Technetium tc99m labeled "tin colloid" was injected into the amniotic cavity, and AF sample was taken 10 minutes later. Furosemide was injected into the amniotic cavity afterwards. Two and 6 hours later, AF samples were obtained. Intestines were harvested at the end of the study. Control group received intraamniotic saline instead of furosemide. Radioactivities of the AF samples and intestines were determined by gamma counter. Clearance of the radioisotope from AF and intestinal accumulation were calculated.

RESULTS

The clearance of the radioisotope from AF was increased significantly in the furosemide group (n = 10) compared with the control group (n = 8; P <.01). Gastrointestinal accumulation of the radioisotope in the furosemide group was 4-fold higher than that the control group (P <.01).

CONCLUSIONS

Induction of fetal diuresis with intraamniotic furosemide accelerates the clearance of intraamniotic substances. This is probably caused by increased urinary output rate, which increases AF volume and consequently results in increased fetal swallowing of AF. In the diseases like gastroschisis and myelomeningocele, in which the contact with AF causes tissue damage, the elimination of meconium from AF in a somewhat natural manner like this method, should be studied further because it may be an alternative minimal invasive in utero treatment modality.

Meconium dependence of bowel damage in gastroschisis

BACKGROUND/PURPOSE

Increasing evidence of physiologic in utero defecation supports the hypothesis that bowel damage in gastroschisis may be meconium dependent. In this study, the author investigated the role of meconium on parameters of bowel damage in a fetal rat model of gastroschisis.

METHODS

Pregnant rats underwent laparotomy at 18 1/2 days gestational age (GA). There were 4 experimental groups of 11 fetuses each; the G(M) group consisted of fetuses with isolated gastroschisis and was considered to have moderate meconium contamination of the amniotic fluid (MCAF); the G(L) group consisted of fetuses with gastroschisis and anal ligation, performed to prevent MCAF; the G(H) group consisted of fetuses with gastroschisis and colon perforation, performed to increase MCAF; and the Sham group consisted of sham operated controls. All fetuses were harvested by cesarean section at 21 1/2 days GA, and the fetal intestine was assessed for peel, intestinal length, intestinal weight per unit length, and histologic appearance.

RESULTS

The authors achieved the following fetal survival rates: G(M) group, 91% (10 of 11); G(L) group, 78% (7 of 9, the ligation was not successful in 2 fetuses); G(H) group, 82% (9 of 11). Sham group, 100% (11 of 11). Intestinal length was decreased in fetuses with gastroschisis, and this reduction was related directly to the grade of MCAF (Sham, 18.4 +/- 0.6; G(L), 11.5 +/- 0.5; G(M), 10.2 +/- 0.6; G(H), 9.1 +/- 0.6 cm; P <.01). In contrast, intestinal weight per unit length increased in fetuses with gastroschisis, and this increase was related directly to the grade of MCAF (Sham, 7.8 +/- 0.5; G(L), 9.4 +/- 0.5; G(M), 11.3 +/- 0.5; G(H), 16.9 +/- 0.7 mg/cm; P <.01). In comparison with the G(M) group, the degree of peel coverage and bowel adherence were increased markedly in the G(H) group, whereas the fetuses of the G(L) group had neither peel nor bowel adherence.

CONCLUSIONS

All bowel damage parameters were affected by MCAF supporting the hypothesis that bowel damage in gastroschisis is at least partially dependent on meconium exposure. Further research is required to clarify other factors that contribute to bowel damage and to identify risk factors that may allow prenatal identification of severely affected fetuses.

Intestinal damage in gastroschisis correlates with the concentration of intraamniotic meconium

BACKGROUND/PURPOSE

Contact with amniotic fluid (AF) causes intestinal damage in gastroschisis, which has been shown to be caused by intraamniotic meconium. However, whether this intraamniotic meconium-induced intestinal damage is concentration dependent has not been investigated previously. The purpose of this study is to investigate the effects of intraamniotic human meconium at various concentrations on the intestines of chick embryo with gastroschisis.

METHODS

Five-day-old fertilized chick eggs were used. Gastroschisis was created through the amniotic cavity without opening the allantoic cavity. Sterile meconium was obtained from newborn humans. Meconium suspensions at various concentrations were prepared using saline and instilled into the amniotic cavity.

RESULTS

Intraamniotic 1:200 and 1:400 meconium was found to cause intestinal damage. Meconium concentrations lower than 1:400 did not cause intestinal damage. Histopathologic examination of the intestines of the 1:200 and 1:400 meconium groups showed serosal thickening, inflammation, focal fibrin, and collagen deposits. Histopathologic features of the intestines of the 1:600 and 1:800 meconium groups did not differ from the intestines of the control group.

CONCLUSION

Intraamniotic meconium, which is responsible for intestinal damage in gastroschisis, must reach a threshold level to induce intestinal damage. J Pediatr Surg 36:1811-1815.

The effects of intraamniotic human neonatal urine and meconium on the intestines of the chick embryo with gastroschisis

BACKGROUND/PURPOSE

Urinary waste products in the amniotic fluid has been implicated as a cause of intestinal damage (ID) in gastroschisis based on the fact that fetus urinates physiologically into the amniotic cavity. However, experimental and clinical data suggest that intrauterine defecation is a physiological event, thus gastrointestinal waste products also may be responsible for ID in gastroschisis. An experimental study was performed to investigate the effects of intraamniotic human neonatal urine and diluted meconium on the intestines of chick embryo with gastroschisis.

METHODS

Five-day-old fertilized chick eggs (Gallus domesticus) were used. Gastroschisis was created through amniotic cavity without opening the allantoic cavity. Sterile urine and meconium were obtained from newborn humans, and 1% meconium suspension was prepared. The eggs were divided in to 3 groups. In the first group, gastroschisis was created, and amniotic fluid was reinstilled without changing its composition (control group). Equal amounts of amniotic fluid and urine mixture was instilled into the amniotic cavity in second group (urine group) and 1% meconium suspension was instilled in similar fashion in the third group after creation of gastroschisis (meconium group).

RESULTS

Histopathologic features of the intestines of the urine group did not differ from the intestines of the control group. The meconium group's bowel showed serosal thickening, inflammation, focal fibrin, and collagen deposits. Histopathologic changes of intestines induced by intraamniotic diluted meconium are consistent with the ones described for human gastroschisis specimens.

CONCLUSION

Gastrointestinal waste products seem responsible for the ID in gastroschisis rather than urinary waste products.

An experimental study investigating the effects of intraperitoneal human neonatal urine and meconium on rat intestines

Urinary waste products (UWP) in the amniotic fluid have been held responsible for the intestinal damage (ID) in gastroschisis, based on the fact that the fetus urinates physiologically into the amniotic cavity. However, experimental and clinical evidence suggests that intrauterine defecation is a physiological event; thus gastrointestinal waste products (GWP) may also be responsible for ID in gastroschisis. An experimental study was performed to investigate the effects of intraperitoneal human neonatal urine and diluted meconium on rat intestines. Adult Wistar albino rats were used. Sterile urine and meconium were obtained from newborn humans and 5% meconium suspension was prepared. Histopathological features of the intestines of the rats injected with urine did not differ from the intestines of the untreated rats. The bowel in rats injected with a meconium suspension showed serosal thickening, inflammation, focal fibrin and collagen deposits. Histopathological changes in intestines induced by intraperitoneal diluted meconium were consistent with those described for human gastroschisis specimens. We conclude that GWP, rather than UWP, seems to be responsible for the ID in gastroschisis.

Discriminant analysis for assessing the value of amniotic fluid microvillar enzymes in the prenatal diagnosis of cystic fibrosis

We have analysed the sensitivity, specificity, and reliability of biochemical diagnosis based on microvillar membrane enzyme assay and using discriminant analysis in amniotic fluid samples obtained from 54 pregnancies at high risk for cystic fibrosis and 125 normal pregnancies. Our results show that amniotic fluid trehalase, alkaline phosphatase, alkaline phosphatase isoenzymes and gamma-glutamyltransferase enzyme activities measured during 16-20 gestational weeks, in spite of their non-specificity for cystic fibrosis, have a very good predictive value for fetal cystic fibrosis or exclude the possibility of the disease. Overall enzyme activity analysis provided over 90 per cent reliability of the method.

Prenatal diagnosis of cystic fibrosis by microvillar enzyme assay on a sequence of 258 pregnancies

Prenatal diagnosis of cystic fibrosis by microvillar enzyme assay on amniotic fluid supernatant has been carried out on 258 sequential pregnancies with a 1 in 4 recurrence risk, all with known outcome. In general the three enzymes evaluated, gamma-glutamyltranspeptidase, aminopeptidase M and the intestinal isoenzyme of alkaline phosphatase, showed a high degree of concordance. However, there were two unusual patterns of microvillar enzyme activity; in seven cases a low gamma-glutamyltranspeptidase activity was associated with elevated values of intestinal alkaline phosphatase, and in ten cases there were isolated low values of intestinal alkaline phosphatase. The former pattern was found to be associated with cystic fibrosis in five cases, while the latter was associated with a normal outcome in all ten cases. A retrospective analysis of enzyme values suggested that the optimal system for minimizing false positives and false negatives was to define foetal cystic fibrosis as a sample where two of the three microvillar enzymes were below a cut-off of half the median value for the gestational week. If such scoring were applied to the cases where conventional microvillar enzyme patterns were observed, the false positive rate was 2.3% and the false negative rate 4.4% between 17 and 20 weeks of gestation.

Microvillar enzyme assays in amniotic fluid and fetal tissues at different stages of development

A systematic study of microvillar enzyme activities in the amniotic fluid in correlation with their values in different fetal tissues during development has been undertaken. Microvillar enzymes appeared in the amniotic fluid at the time of disappearance of the anal membrane, 12-13 weeks, and declined from the 18th week until the 24th week. The study of fetal tissues and fluids has shown that gamma-glutamyltranspeptidase is mainly of liver origin. The significant decrease of the activities of these amniotic fluid enzymes has been the basis of prenatal diagnosis of cystic fibrosis. These assays may be useful for the diagnosis of certain digestive tract abnormalities at later stages of pregnancy.

Gamma-glutamyl transferase activity in the amniotic fluid of fetuses with chromosomal aberrations and inborn errors of metabolism

The activity of gamma-glutamyl transferase (GGT) was measured in amniotic fluid collected between the 16th and 30th weeks of gestation from 81 pregnancies with fetuses affected by chromosomal aberrations, nine with different types of inborn errors of metabolism, two with hemophilia A and one with fragile X syndrome. The GGT activity was compared with that from 1000 normal pregnancies and deliveries resulting in healthy newborns. Contamination of amniotic fluid by blood did not affect the GGT activity. Pathologically decreased activity was found in 25 of 56 amniotic samples from pregnancies with fetal autosomal chromosomal aberrations (44.6%). It was decreased in 15 of 35 pregnancies with fetal trisomy 21 (43%), in 11 of 19 pregnancies with fetal trisomy 18 (58%), in one of three pregnancies with fetal trisomy 13 and in two pregnancies with fetal trisomy 8 and triploidy, respectively. In only three of 16 pregnancies with fetal sex chromosomal aberrations was the GGT activity low. Increased GGT activity was found in three of six pregnancies with unbalanced structurally rearranged karyotypes of the fetuses. Normal GGT activity was observed in all nine amniotic fluid samples from pregnancies with fetuses affected with different forms of inborn errors of metabolism diseases, in the two pregnancies with hemophilia A and in the pregnancy with a male fetus with fragile X syndrome. These and earlier findings indicate that the GGT activity in amniotic fluid is mostly decreased in pregnancies with severe fetal developmental abnormalities, such as autosomal chromosomal aberrations, which could possibly be secondary to an alteration of the microvillar transport system of GGT to the amniotic fluid.(ABSTRACT TRUNCATED AT 250 WORDS)

Fetal diagnosis of inborn errors of metabolism

Nearly 4000 different human disorders are supposed or known to be due to a single gene mutation. In about 10%, an early diagnosis is possible by the demonstration of specific abnormalities of metabolites in blood and/or urine, an abnormal structure/function of a particular (enzyme) protein or by the (in)direct demonstration of the gene mutation using DNA analysis. These methods of molecular analysis can often also be used for carrier detection. Early identification of couples at risk of handicapped offspring followed by genetic counselling forms the basis for prevention. Follow-up studies have shown that more than half of the couples at risk of a child with a genetic disease refrain from pregnancy. An important alternative for couples at risk is prenatal monitoring and selective abortion. During the last 10-15 years, the technology of fetal diagnosis of genetic diseases has improved and the number of Mendelian disorders that can be diagnosed in utero has increased to more than 100. In the second-trimester of pregnancy, about two dozen inborn errors of metabolism have been diagnosed by metabolite analysis of amniotic fluid supernatant using gas chromatography-mass spectrometry or electrophoretic methods. About 5000 pregnancies at risk of different types of haemoglobinopathy, haemophilia, alpha-1-antitrypsin deficiency and a few other diseases not expressed in amniotic fluid cells have been investigated by biochemical analysis after fetal blood sampling. The most common approach towards fetal diagnosis of inborn errors of metabolism has been the demonstration of a specific enzyme deficiency in cultured amniotic fluid cells. In this way some 60 different diseases have been diagnosed, usually after 2-4 weeks of cultivation after amniocentesis at 16 weeks gestation. In addition, some 20 other Mendelian disorders have been diagnosed in utero by ultrasonography and non-biochemical analysis of amniotic fluid cells or fetal skin biopsies. The introduction of chorionic villus sampling has offered the possibility of first-trimester fetal diagnosis of a large number of Mendelian disorders. The overall diagnostic experience until mid-1986 amounts to about 1500 pregnancies at risk. Some 45 different inborn errors have been diagnosed by enzyme assays directly on chorionic villus homogenate or after incubation with radiolabelled precursors of intact villi followed by chromatography or other types of analysis. In a few instances, cell cultivation for a period of 2-3 weeks is required to establish a reliable biochemical diagnosis.

Fetal diagnosis of cystic fibrosis

Two different methods of prenatal diagnosis of CF are currently available. Both are usually only suitable for couples with a 1 in 4 risk of bearing an affected child. The method of choice is first trimester diagnosis on a chorionic villus sample using linked DNA probes. The advantages are: 1. The very high degree of accuracy of diagnosis, 2. The opportunity of first trimester termination of pregnancy when the fetus is affected. The disadvantages are: 1. The need for a blood sample from an index affected child to establish phase, 2. The requirement for early workup of the nuclear family to ascertain informativeness, 3. The chance that some families will be uninformative or only partially informative for available DNA probes. An alternative form of diagnosis is that using microvillar enzyme testing on second trimester amniocentesis samples. The advantages are: 1. It is suitable for all pregnancies with a 1 in 4 risk of CF, 2. No prior workup of the family is required, 3. Assays can be completed within one hour of receipt of the sample. The disadvantages are: 1. The accuracy of diagnosis leaves some scope for error, 2. If termination of pregnancy is indicated this can only be carried out at about 18 or 19 weeks of gestation.

An abnormal pattern of amniotic fluid microvillar enzymes signalling fetal cystic fibrosis

We have observed seven pregnancies at risk for fetal cystic fibrosis where second-trimester amniotic fluid microvillar enzyme activities presented an unusual pattern. Low gamma-glutamyltranspeptidase and borderline alpha-glucosidase values were associated with normal aminopeptidase M and intestinal alkaline phosphatase values. All seven pregnancies went to term; five of the seven infants were affected with cystic fibrosis.

Prenatal detection of intestinal obstructions, aneuploidy syndromes, and cystic fibrosis by microvillar enzyme assays (disaccharidases, alkaline phosphatase, and glutamyltransferase) in amniotic fluid

Microvillar enzymes (disaccharidases, alkaline phosphatase, and gamma-glutamyltransferase) were assayed in amniotic fluid from pregnancies with normal and abnormal fetuses to determine their specificity and reliability for the prenatal detection of intestinal obstructions and cystic fibrosis. All fetuses with imperforate anus, duodenal atresia, jejuno-ileal atresia, multiple intestinal atresia, or other forms of intestinal obstructions, with or without associated ventral wall defect or aneuploidy syndrome, showed diminished microvillar enzyme activities below the normal range of control amniotic fluid samples. The exclusively intestinal hydrolases maltase, sucrase, palatinase, and alkaline phosphatase were the most reliable and sensitive markers to detect intestinal obstructions whereas more widely distributed trehalase and gamma-glutamyltransferase activities were less sensitive. The combination of intestinal disaccharidase maltase, sucrase or palatinase and ALP assays is more accurate for prenatal diagnosis of CF than a combination of intestinal ALP and GGTF assays.

Prenatal detection of cystic fibrosis; comparative study of maltase and alkaline phosphatase activities in amniotic fluid

The potential value of microvillar enzymes in the prenatal diagnosis of cystic fibrosis (CF) has previously been demonstrated and is corroborated in the present comparative study. Maltase and alkaline phosphatase (ALP) activities were studied in the amniotic fluids of 57 pregnancies with a 1 in 4 risk for CF or with a known CF outcome and in 489 controls. A simple assay for maltase activity (MU-maltase) with the fluorogenic substate 4-methylumbelliferyl alpha-glucoside, offers great technical advantages and an at least equal detection rate of CF, when compared to the previously used test with maltose as substrate. Intestinal ALP was estimated either as phenylalanine inhibitable activity (PI-ALP) or as the proportions of residual activity in the presence of the inhibitors phenylalanine or homoarginine. MU-maltase and PI-ALP appeared the most successful methods: both tests were able to detect 14 of the 16 (88 per cent) pregnancies with fetal CF. Each of the two tests alone also allowed a correct prediction in 24 of the 25 pregnancies at risk but with normal outcome; however all 25 cases could be correctly predicted by a combined evaluation. It is suggested that more than one intestinal enzyme activity should be evaluated to allow optimal results in the prenatal monitoring of pregnancies at high risk for CF.

Fetal intestinal microvilli in human amniotic fluid

The intestinal microvilli of fetal origin in human amniotic fluid were purified by Ca2+ precipitation of contaminating organelles followed by differential centrifugation of microvillar membranes. In the purified preparation, the specific activity of the microvillar marker-enzymes maltase and sucrase increased about 77-fold over that in cell-free amniotic fluid. Significant contamination of the purified preparation by endoplasmic reticulum (microsomes) and lysosomes was ruled out on the basis of a low content of the marker enzymes glucose-6-phosphatase (microsomes) and acid phosphatase (lysosomes). Amniotic fluid microvilli contain typical enzymes of the fetal intestine including maltase, sucrase, trehalase, alkaline phosphatase and gamma-glutamyltransferase, and their morphology by electron microscopy resembles that of vesiculated intestinal microvilli. Prenatal detection of genetic diseases due to a deficiency of a protein expressed in these membranes or associated to abnormal microvilli seems feasible.

Biochemical analysis of meconium in fetuses presumed to have cystic fibrosis

A series of proteins (albumin, transferrin, alpha 1-antitrypsin, alpha-fetoprotein and pancreatic oncofetal antigen) and enzymes (gamma-glutamyltranspeptidase, aminopeptidase M, alkaline phosphatase, alpha-glucosidase and protease) was measured in fetal meconium extracts. There were 19 fetuses thought to have cystic fibrosis (CF), 13 with neural tube defects, three with chromosome abnormalities and 19 normal controls, all with gestational ages between 18 and 21 weeks. With the exception of alpha-fetoprotein, all the proteins and enzymes were significantly elevated in the CF meconium extracts. The most definitive indicator of a CF fetus was the albumin concentration, where the mean level was five times that found in the control groups. However, five of 19 fetuses assumed to have CF had albumin in the normal range. In these cases the meconium protease levels were grossly elevated. Furthermore, in the same five fetuses meconium concentration of pancreatic oncofetal antigen, a protein synthesized in the fetal pancreas, was also greatly raised. We suggest that post-mortem examination of a fetus thought to have CF should include measurement of meconium albumin, protease and pancreatic oncofetal antigen.