Analysis of liver/bone/kidney alkaline phosphatase mRNA, DNA, and enzymatic activity in cultured skin fibroblasts from 14 unrelated patients with severe hypophosphatasia.

Hypophosphatasia is a heritable disorder characterized by defective bone mineralization and a deficiency of liver/bone/kidney alkaline phosphatase (L/B/K ALP) activity in serum and tissues. Severe forms of the disease, which are generally lethal in infancy, are inherited in an autosomal recessive fashion. The gene defects that produce hypophosphatasia are poorly understood, but many are likely to occur at the L/B/K ALP locus. To investigate these gene defects, we analyzed L/B/K ALP DNA, RNA, and enzyme activity in cultured dermal fibroblasts from 14 patients with perinatal or infantile hypophosphatasia and from 12 normal individuals. Southern blot analyses of the L/B/K ALP genes from patients and controls revealed identical restriction patterns. Control fibroblast ALP activity correlated with the corresponding L/B/K ALP mRNA levels estimated by blot hybridization analysis and densitometry (r = .94, P less than .0001). In contrast, fibroblasts from the hypophosphatasia patients were deficient in ALP enzyme activity but expressed apparently full-sized L/B/K ALP mRNA at normal levels. Bone specimens from one of the patients were examined and found to be deficient in histochemical ALP but contained immunologic cross-reactive material detected by anti-human liver ALP antiserum. Our results demonstrate that the deficiency of ALP activity in fibroblasts from 14 patients with severe hypophosphatasia is not due to decreased steady-state levels of the corresponding mRNA. The presence of enzymatically inactive L/B/K ALP protein in one of these patients is consistent with a point mutation or small in-frame deletion in the coding region of L/B/K ALP gene.     

Prenatal diagnosis of Sanfilippo disease type B

Summary The prenatal diagnosis of a fetus affected with Sanfilippo disease type B is described. The deficiency of -N-acetylglucosaminidase in the cultured amniotic fluid cells was shown by a microassay enabling early prenatal diagnosis. In addition an increased level of heparan sulphate was demonstrated in the amniotic fluid by two-dimensional electrophoresis of glycosaminoglycans. The latter result confirmed the value of this test as an adjunctive method in the prenatal diagnosis. The pregnancy was terminated and the prenatal diagnosis was confirmed by enzyme analysis of cultured fetal fibroblasts and fetal liver.     

Genotyping and prenatal assessment of collagen lysyl hydroxylase deficiency in a family with Ehlers-Danlos syndrome type VI.

Collagen lysyl and prolyl hydroxylase activities were measured in cultured fibroblasts from a child with clinical features of Ehlers-Danlos syndrome. Lysyl-to-prolyl hydroxylase activity ratios in cells from the proband, mother, father, and control were .24, .86, .52, and 1.00, respectively, providing a biochemical diagnosis of Ehlers-Danlos syndrome type VI and indicating an autosomal recessive mode of inheritance in this family. Prenatal assessment of lysyl hydroxylase deficiency was requested and accomplished for the first time during a subsequent pregnancy in the family. A series of control cultures established lysyl hydroxylase activity to be similar in cultured amniotic fluid cells (AF and F cells) and in cultured dermal fibroblasts. Cultured F and AF cells from the monitored pregnancy had enzyme activity similar to controls, indicating that the fetus should not be affected by lysyl hydroxylase deficiency. This finding was confirmed by demonstration of normal lysyl hydroxylase activity in fibroblasts cultured from the newborn baby. These studies show that cells cultured from second trimester amniotic fluid have collagen lysyl hydroxylase activity similar to that in dermal fibroblasts, making prenatal diagnosis of lysyl hydroxylase deficiency possible.     

Rapid prenatal testing for human beta-glucuronidase deficiency (MPS VII)

Prenatal diagnosis for the lysosomal storage disorders is typically achieved by enzymatic analysis of the relevant lysosomal enzyme in cultured amniocytes or chorionic villi. While prenatal diagnosis of some genetic diseases can be done by analysis of pertinent metabolites in amniotic fluid, there are few data regarding prenatal diagnosis of lysosomal disorders by enzyme analysis of amniotic fluid. Prenatal diagnosis by enzyme analysis of amniotic fluid has the potential advantage of providing a more rapid prenatal test result. In this study we describe an assay for the prenatal diagnosis of the mucopolysaccharidosis beta-glucuronidase deficiency (MPS VII; MIM #253220) using amniotic fluid and we confirm its reliability in detecting an affected fetus in an at-risk pregnancy by enzyme analysis of cultured amniocytes and fetal fibroblasts. Because MPS VII is rare and few instances of prenatal diagnosis for this and nearly all other lysosomal disorders have been accomplished by enzyme analysis of amniotic fluid, confirmation of results obtained from enzyme analysis of amniotic fluid should be carried out by enzyme or mutation analysis using cultured amniocytes or chorionic villus specimens.     

Citrullinemia: prenatal diagnosis of an affected fetus.

We monitored a pregnancy in a family at risk for citrullinemia due to argininosuccinic acid (ASA) synthetase deficiency. ASA synthetase activity in cultured epithelioid amniotic fluid cells from the fetus at risk was less than 2% of control epithelioid amniotic fluid cell activity. An increased concentration of citrulline was found in the at-risk amniotic fluid (0.14 mumol/ml) as compared with fluid from six controls and one at-risk but unaffected pregnancy (trace). The pregnancy was terminated, and the in utero diagnosis was confirmed by assay of ASA synthetase activity in cultured fetal skin fibroblasts (4.4% of control activity). In addition, all five fetal tissues studied had significant accumulation of citrulline, whereas control fetal tissues had none. These data provide evidence that, if precise control is maintained over tissue culture variables, citrullinemia can be diagnosed successfully in utero by microassay of ASA synthetase activity in cultured amniotic fluid cells. They also suggest that amniotic fluid citrulline concentrations provide strong adjunctive evidence for this prenatal diagnosis.     

Argininosuccinic aciduria: prenatal studies in a family at risk.

We have monitored two successive pregnancies in a family which we found to be at risk for argininosuccinic aciduria. We measured argininosuccinic acid (ASA) concentrations in amniotic fluid and utilized an indirect assay of ASA lyase activity in cultured amniotic fluid cells. The assay procedure is based on the uptake of 14C from [14C]citrulline and of [3H]leucine into protein. ASA was easily measured in amniotic fluid from the first fetus at risk, whereas none was detectable in control fluids. Amniotic fluid cells cultured from this fetus had only 5.5% of control ASA lyase activity. The pregnancy was terminated, and hepatic ASA lyase activity in the fetus was shown to be about 1.3% of control values. In addition, eight fetal tissues were analyzed for ASA, and all had significant accumulation. ASA was not detected in amniotic fluid from the second fetus at risk, and ASA lyase activity in cultured cells was 80% of control activity. Enzymatic analysis of erythrocyte lysate confirmed the diagnosis of an unaffected child (ASA lyase = 46% of control) and indicated heterozygosity. Thus, we provide further evidence that argininosuccinic aciduria can be diagnosed successfully in utero by indirect assay of ASA lyase activity in cultured amniotic fluid cells. In addition, high amniotic fluid ASA concentrations provide strong adjunctive evidence for such a prenatal determination, and may prove to be sufficient for diagnosis.     

Prenatal diagnosis of inborn errors of metabolism. Present status and new approaches

The evolution of the techniques aiming at the prenatal diagnosis of inborn metabolic disorders has closely reflected the progress in the knowledge of their underlying molecular defects. Initially, abnormal metabolites have been looked for in amniotic fluid. Recently, improved techniques of detection have permitted fast and reliable prenatal diagnoses through biochemical studies of cell-free amniotic fluid. Presently, the most widely used approach is the search for the defective gene product in cultured amniotic cells obtained through amniocentesis. Because of its relative safety, this procedure should be recommended, provided three prerequisites are met: a most accurate diagnosis of the index patient, the knowledge of the defective enzyme and its expression in cultured cells. For a correct interpretation of the results, cell culture parameters as well as specific activities of the mutant enzyme in the index case and the parental cells must be taken into account. Fetal blood sampling is a valuable alternative for some of the genetic disorders that cannot be detected in cultured amniocytes. The recently developed technique of chorion biopsy enables now to sample fetal cells during the first trimester of gestation. Meanwhile, the progress in DNA technology has uncovered exciting perspectives for the prenatal diagnosis of monogenic disorders at the gene level. Restriction endonuclease mapping has enabled to diagnose prenatally some forms of haemoglobinopathies, first through the polymorphism of sequences adjacent to the beta-globin gene, and now for the sickle-cell disease, by direct identification of the mutation.     

Heterogeneity for adenosine deaminase deficiency: Expression of the enzyme in cultured skin fibroblasts and amniotic fluid cells.

Adenosine deaminase (ADA) could be quantitated and the isozyme pattern characterized in cultured amniotic fluid cells. In 20 amniotic fluid cell cultures the mean specific activity was 14.3 U/g protein +/- 6.7 (SD) and compared favorably with values of 14.6 U/g protein +/- 6.8 (SD) observed in 26 cultures of skin fibroblasts. In cultures of skin fibroblasts established from two obligate heterozygotes for ADA deficiency, the specific activity of ADA was 7.0 and 7.7 U/g protein. The ADA isozyme pattern that existed in cultures of amniotic fluid cells was the same as that observed in cultured skin fibroblasts. This identification of the same apparent enzyme may permit the prenatal diagnosis of that form of combined immunodeficiency disease caused by ADA deficiency. Residual enzyme activity of less than 1% and 10% of the mean of normal fibroblasts could be measured in cultured fibroblasts from two unrelated children with ADA deficiency and combined immunodeficiency disease. The tissue-specific enzyme from cultured skin fibroblasts from the child with 10% residual activity had a faster electrophoretic mobility and greater heat stability than normal ADA. This enzymatic evidence indicates that at least two mutant alleles exist at the locus for ADA which predispose to combined immunodeficiency disease when present in the homozygous state.     

Prenatal diagnosis of congenital anomalies in an intrauterine growth retarded fetus

Summary Chromosome analysis of amniotic fluid cells and amniotic fluid alpha-fetoprotein determinations were used to investigate a fetus with severe intrauterine growth retardation in the third trimester. The karyotype was 47,XY,18+ and increased alpha-fetoprotein levels indicated the presence of congenital malformations. We suggest that when severe fetal growth retardation is detected early in the antepartum course, amniotic fluid alpha-fetoprotein and amniotic fluid cell chromosome studies be done to determine if congenital anomalies may be an etiological factor.     

Prenatal Diagnosis of Tay-Sachs Genotypes

Hexosaminidase activity was determined in cultured and uncultured amniotic fluid cells taken from seven pregnant women who had previously given birth to infants with Tay-Sachs disease. Complete deficiency of hexosaminidase A was found in one case, indicating a Tay-Sachs fetus. The diagnosis was confirmed on examination of various tissues after therapeutic abortion. Of the other six cases three were considered heterozygous and three homozygous normal. These diagnoses were confirmed postnatally on examination of cord blood leucocytes, peripheral leucocytes, and urine. The activity of hexosaminidase A is appreciably decreased in dead cells and hence in uncultured amniotic fluid cells. Hence reliable identification in utero of the three genotypes may be achieved only by examining the cultured living amniotic cells.     

Prenatal diagnosis of Tay-Sachs disease. Reflectometry of hexosaminidase A,B, and C/S bands on zymograms

Summary Hexosaminidase (Hex) A, B, and C/S were electrophoretically separated from cultured amniotic fluid cells, fetal brain, and white blood cells. Photographs of cellulose acetate zymograms were evaluated by reflectometric scanning. The usefulness and limitations of this rapid method were shown. Hex A was completely absent in the amniotic fluid cells of one out of three pregnancies at risk for Tay-Sachs disease, but Hex C/S was present in this case. The prenatal diagnosis of Tay-Sachs disease was made, and confirmed with the fetal material after abortion. Hex C/S was distinguishable from a residual or heterozygous Hex A activity. In the two other risk pregnancies, reflectometric Hex A activities were found to be 50 and 34% of control; the heterozygous stage was presumed for the fetuses.     

Prenatal enzymatic diagnosis of Krabbe disease (globoid-cell leukodystrophy) using chorionic villi

Summary Sixteen pregnancies in families with children enzymatically diagnosed as having Krabbe disease (KD) were monitored for prenatal KD using the assay of galactosyl ceramide -galactosidase (GCG) in uncultured chorionic villi (CV), cultured CV, or cultured amniotic fluid cells (AFC). Prenatal KD diagnoses were made for 5 pregnancies on the basis of lower than 10% normal GCG activity in cultured CV or AFC. Uncultured CV were studied in 3 out of the 5 KD embryos, although the GCG activities of 14%–23% as compared with control villi were diagnostically inconclusive; the relatively high activities were considered to be caused by maternal GCG contamination of these very small villus samples. Although the villi from 6 of the other pregnancies yielded more conclusive results, the use of uncultured CV alone is not recommended for prenatal KD diagnosis, this material being subject to possible uncontrolled contamination with maternal enzyme.     

In utero diagnosis of Gaucher disease.

Beta-Glucosidase activity measured by synthetic substrate at pH 4.6 was low in the cultured amniotic cells from two pregnant women at risk for juvenile and adult type Gaucher disease. The diagnosis was confirmed by showing a low activity of beta-glucosidase in the skin fibroblasts with a synthetic substrate or in the spleen with a natural substrate, and by ascertaining the presence of Gaucher cells in the fetal tissues. However, considerable activity of beta-glucosidase measured with synthetic substrate was found in the liver of both affected fetuses and in the spleen of one. It is advisable that the determination of beta-glucosidase to confirm prenatal diagnosis of Gaucher disease be done either in the cultured skin fibroblasts or in the spleen, and if in the spleen, with a natural substrate rather than a synthetic one.     

Antenatal diagnosis of glutaric acidemia

Two pregnancies at risk for glutaric acidemia were monitored. In one, in which the fetus was not affected, glutaric acid was not detected in the amniotic fluid at amniocentesis (15 weeks) and the glutaryl-CoA dehydrogenase activity of cultured amniotic cells was normal. In the other, a marked elevation of glutaric acid in the amniotic fluid, together with deficiency of glutaryl-CoA dehydrogenase in amniotic cells, prompted termination of the pregnancy, and studies on the abortus confirmed the diagnosis of glutaric acidemia. Glutaric acidemia, is, thus, another inborn error of metabolism which can be diagnosed in utero.     

THE NATURE AND ORIGIN OF THE SOLUBLE PROTEIN IN HUMAN AMNIOTIC FLUID

1. Amniotic fluid surrounds the human fetus and is separated from the uterus by the amnion, chorion and placenta. The ability to obtain samples of amniotic fluid from women by a simple procedure has encouraged studies on the nature and origin of the fluid, and on its use for the diagnosis of a variety of clinical conditions. The fluid contains cells, which are of fetal origin, and can be grown in a tissue culture. Cyto-genetic and biochemical analyses can therefore be used to detect chromosomal aberrations and inborn errors of metabolism in the fetus. 2. The supernatant of amniotic fluid contains many of the solutes typical of extracellular fluid. In particular, it contains a wide range of proteins and those which are of fetal origin are likely to be of use in the prenatal diagnosis of fetal disease. This review examines the nature and origin of the soluble protein in amniotic fluid, and discusses the diagnostic uses of the proteins which are of fetal origin. 3. In other mammals, the arrangement of the fetal membranes is different from that in man, and these differences are reflected by changes in the nature of the amniotic fluid. Thus data from other animals have little applicability to man. 4. Electrophoresis and immunoelectrophoresis have established that the major proteins in amniotic fluid are also present in maternal and fetal sera. Their concentrations in the fluid are influenced by their molecular weight and proteins larger than about 2.5 times 10⁶ may be excluded. Towards term, phenotyping studies show that a number of serum proteins in amniotic fluid are of maternal origin. In the case of group-specific component (Gc) this has been shown to be so throughout pregnancy. Such proteins must enter the fluid by diffusing across either the chorion or the chorionic plate and then the amnion. 5. It has been previously claimed that various serum proteins in amniotic fluid are of fetal origin. For albumin and IgG there are data that strongly support a maternal origin. The evidence on the origin of insulin is inconclusive. The concentration of β₂-microglobulin in amniotic fluid exceeds that in maternal serum and is probably too high also for fetal serum to be its major source. It has a wide tissue distribution and probably enters the fluid from surrounding structures. 6. Alpha-fetoprotein in amniotic fluid is of fetal origin as it is present in maternal serum at far lower concentrations. It is found in fetal serum, urine and yolk sac, but it is not clear how it enters the amniotic fluid of normal fetuses. The concentrations of Gc and alpha-fetoprotein have been measured in amniotic fluid and in their sera of origin. The relative concentration of Gc in amniotic fluid was found to be much greater than that of alpha-fetoprotein and the concentration gradients of these marker proteins can be compared with data for other proteins. In this way further evidence has been obtained that the albumin, α₁,-antitrypsin and transferrin in amniotic fluid are mainly of maternal origin throughout pregnancy. 7. Immunological studies have shown that at least three proteins of non-serum origin are present in amniotic fluid and they have also been located in the amnion and uterine decidua. 8. The enzymes present in amniotic fluid are summarized. Many lysosomal enzymes are clearly of fetal origin since they show altered specific activities in the appropriate cases where the fetus is affected with an inborn error of metabolism. For other enzymes, analysis of specific activity gradients can help to decide the extent to which an enzyme is of serum origin, although this will not exclude the possibility of a maternal (uterine) contribution. The results of such analyses suggest that, relative to the serum protein in amniotic fluid, the greatest concentrations of the minor non-serum proteins in the fluid occurs between thirteen and eighteen weeks of pregnancy and also towards term. 9. Some inborn errors of metabolism may be diagnosed prenatally by measuring the specific activity of the respective enzyme in amniotic fluid. However, the presence of different enzymes with similar substrate specificities has prevented this in Pompe's disease. 10. In cases where the fetus is affected with anencephaly or spina bifida there is an increase in the concentration of alpha-fetoprotein in the amniotic fluid. This has provided a way of detecting these diseases early enough to allow termination of pregnancy. 11. The discovery of new proteins in fetal serum and in the tissues surrounding the amniotic cavity would seem to provide the best chance of extending the uses of amniotic fluid into the other areas of prenatal medicine.     

Immunosuppressive properties of mouse amniotic fluid.

Previous reports have suggested that the alpha-fetoprotein present in mouse amniotic fluid is a potent nontoxic immunosuppressant. In the present studies mouse amniotic fluid (1:50) from 9- to 20-day gestations markedly inhibited the in vitro responses of mouse spleen cells to SRBC, and spleen cells from nonpregnant females were more affected than were cells from pregnant mice. On the other hand, MAF was less effective in depressing antigen- and mitogen-induced proliferation of human blood cells than were NMS or human serum. Human AF and cord sera did not significantly depress the immune responses of cells from mouse or man when added to cultures at concentrations sufficient to achieve levels of alpha-fetoprotein reported to be immunosuppressive if mouse AFP is used. While these studies do not identify the inhibitory agent(s) present in MAF, they do suggest that mouse AFP either is pharmacologically different from human AFP and/or that the immunosuppressive activity attributed to mouse AFP is actually produced by another agent physically associated with it.     

Genetic variability of alkaline phosphatase expression in inbred mouse tissues

Quantitative alkaline phosphatase (ALP; EC 3.1.3.1) expression varies among various tissues and among inbred mouse strains. There is about a 20-fold difference in ALP activity in lungs from CBA/J and C57L/J inbred strains and this difference is inherited additively with a heritability of 0.84. Studies of thermostability at 56 and 65° C and sensitivity toward inhibitors (l-phenylalanine, l-homoarginine, l-phenylalanylglycylglycine, and levamisole) do not demonstrate differences in the ALP from lungs or liver of the CBA/J and C57L/J strains. The ALP activity in intestine expressed by the intestinal locus varies over 100-fold between A/J and DBA/1J strains. Further studies of the mechanisms resulting in this difference in ALP activity should help elucidate the mechanisms for aberrant expression of ALP in malignancy and for manipulation of low ALP activity in hypophosphatasia.This work has partially supported by NIH Grants GM-27018, GM-20138, GM-07511.     

Glial origin of rapidly adhering amniotic fluid cells.

Rapidly adhering cells (RA cells) from the amniotic fluid of a pregnancy with fetal anencephaly were investigated by immunofluorescence assay with an antiserum against glial cells. After 24 hours'' cultivation a high proportion of the cells showed positive glial-specific fluorescence, whereas no staining was seen in cells from samples of normal amniotic fluid. At the 24th week the mother was delivered of a stillborn infant with anencephaly. Immunofluorescence staining of RA cells with glial-specific antiserum may be used for the differential diagnosis of fetal abnormalities associated with a high alpha-fetoprotein concentration in amniotic fluid.     

Amniotic fluid cell morphology in early antenatal prediction of abortion and low birth weight.

The morphology of rapidly adherent (RA) amniotic fluid cells was examined in 201 pregnant women referred for amniocentesis because of two sequential high serum alpha-fetoprotein (AFP) concentrations. Out of 43 amniotic fluid samples containing increased amounts of AFP, 42 had neural or peritoneal cells predominating among the RA cells, the outcome being an infant with a neural-tube defect or exomphalos. In the other case with a raised amniotic fluid AFP concentration but only anterior placental cells the infant was normal. In 25 amniotic fluid samples containing normal amounts of AFP distinctive new patterns of RA cells were observed, termed fetal distress cells. These pregnancies resulted in five spontaneous abortions and 20 infants with birth weights under 2500 g. Fetal distress cells were not detected in any of the remaining 133 samples. One pregnancy was terminated because of a chromosomal abnormality, and there were seven twin pairs not recognised on ultrasonography before amniocentesis. The remaining 125 pregnancies went to term, resulting in infants with birth weights exceeding 2500 g. The results suggest that RA-cell morphology will prove to be of value in the early antenatal prediction of spontaneous abortion and low birth weight.     

Transport and storage of amniotic fluid samples for prenatal diagnosis of metabolic diseases

Summary 1. A method for freezing uncultured amniotic fluid cells is presented, which allows their use as pregnancy-age matched controls in prenatal diagnosis of metabolic diseases. 2. Amniotic fluid cells were successfully cultured after up to 7 days in transport, which makes prenatal diagnosis available to parents living a long way from specialized centers.

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Zusammenfassung 1. Eine Einfriermethode für nichtkultivierte Fruchtwasserzellen wird beschrieben, wodurch man diese wie Kontrollmuster anwenden kann bei pr?nataler Diagnostik von Stoffwechselkrankheiten. 2. Fruchtwasserzellen wurden erfolgreich kultiviert nach langzeitigem Transport (7 Tage); dieser Befund bringt eine pr?natale Diagnostik im Bereich entfernt von spezialisierten Zentren lebender Eltern.