Normal blood cell values in the early mid-trimester fetus

Samples of pure fetal blood from 116 fetuses of 15–21 weeks' gestation were obtained by direct vision fetoscopy. Ninety nine of these fetuses, presumed to be haematologically normal, were suitable for analysis. The data obtained show that the erythropoietic system is evolving rapidly in this gestational age range. The myeloid series shows no significant increase or decrease in numbers apart from eosinophils and basophils which increase significantly with gestational age whereas the platelet count remains constant. The growing application of fetoscopic blood sampling to the prenatal diagnosis and management of fetal blood disorders renders mandatory a knowledge of normal fetal blood values.     

Prenatal diagnosis of citrullinaemia: Review of a 10-year experience including recent use of DNA analysis

Prenatal diagnosis of citrullinaemia has been accomplished by three different methods to date: (1) enzyme assay of cultured fetal cells; (2) quantification of citrullirie in amniotic fluid supernatant; and (3) incorporation of [¹⁴C]citrulline into protein by cultured fetal cells. Our laboratory has used these methods to perform prenatal diagnosis for 28 fetuses over a 10-year period. More recently, DNA polymorphisms were used for prenatal diagnosis by linkage analysis. Of the 28 fetuses studied, 23 were predicted to be unaffected, four were predicted to be affected, and results were conflicting in one case where [¹⁴C]citrulline incorporation erroneously indicated an affected fetus but linkage analysis correctly predicted an unaffected fetus. Because of low levels of enzyme activity in heterozygotes and in certain amniotic fluid cell types, biochemical diagnosis of citrullinaemia is complicated by the risk of false affected results, although [¹⁴C]citrulline incorporation is relatively reliable. When informative, linkage analysis is the preferable method for cases with a 25 per cent risk. The risk of false affected results makes prenatal diagnosis for cases with less than 25 per cent risk of questionable value.     

Mucolipidosis type IV: Accumulation of phospholipids and gangliosides in cultured amniotic cells. A tool for prenatal diagnosis

Cultured amniotic fluid cells from two mucolipidosis type IV (MLIV)-affected fetuses demonstrated accumulation of phospholipids and gangliosides when compared with normal controls. Like cultured skin fibroblasts from MLIV patients, cultured amniotic cells from the affected fetuses accumulated primarily lyso phospholipids and this could be demonstrated by radioactive labelling with appropriate precursors, either inorganic phosphate or oleic acid. Furthermore, like cultured skin fibroblasts, there was significant retention of exogenously supplied GDIA ganglioside in the affected amniotic cells. This storage was previously demonstrated to be unique to MLIV and thus can be used at present as a specific procedure for prenatal diagnosis of MLIV.     

First-trimester diagnosis of hunter syndrome: Very low iduronate sulphatase activity in chorionic villi from a heterozygous female fetus

Iduronate sulphatase activity was determined in uncultured chorionic villi from four fetuses at risk for Hunter syndrome. AH fetuses were shown to be female by chromosome analysis. Biopsy material from three fetuses showed iduronate sulphatase activity within normal limits whilst the fourth fetus showed activity reduced to 7 per cent of our control mean. The importance of fetal sexing in prenatal diagnosis of this condition is emphasized as female carrier fetuses may show iduronate sulphatase activity reduced to levels observed in affected males.     

First-trimester prenatal diagnosis of spinal muscular atrophy using microsatellite markers

Twenty-five pregnancies at risk for spinal muscular atrophy I (SMA I) have been monitored by first-trimester prenatal diagnosis. Microsatellite markers were used in all cases to amplify polymorphic regions at the D5S125, D5S435, D5S39, D5S127, and D5S112 loci. All families, including 12 SMA I pedigrees with a deceased index child, were fully informative for DNA analysis. Three fetuses were predicted to be affected and 22 fetuses were predicted to be unaffected. Twenty-two newborns were unaffected by clinical examination at birth. These results support the accuracy of SMA I prenatal diagnosis based on linkage analysis.     

Prenatal diagnosis of Pompe's disease (type ii glycogenosis) in chorionic villus biopsy using maltose as a substrate

Uncultured trophoblasts obtained from chorionic villus biopsy during the gestation period of 8–12 weeks were assayed for alpha-glucosidase activity using maltose as the substrate. Only one major form of maltase activity with a pH optimum at 4.0 was demonstrated. Using this method, we performed prenatal diagnosis on three pregnancies at risk for the infantile form of type II glycogen storage disease. Two affected fetuses and one unaffected fetus were predicted and the diagnosis was subsequently confirmed. The maltose assay offered a direct, simple, and sensitive method for prenatal diagnosis of Pompe's disease in the first trimester.     

First trimester prenatal diagnosis of haemophilia A: Two years' experience

We evaluated the feasibility, reliability, and acceptability of prenatal diagnosis of haemophilia A by DNA analysis of chorionic villi. Twenty-two women at risk to transmit the abnormal gene were referred for prenatal diagnosis, two of them twice. Two of the 22 women appeared to be non-carriers by DNA analysis. In one of these women, the results were known only after chorionic villus sampling had been carried out. Thirteen of the twenty carriers were heterozygous for an intragenic (Bell or Xbal) marker; six women were only heterozygous for the extragenic DXS52 (Stl4) locus. One of the women was homozygous for all the presently known DNA markers within or closely linked with the factor VIII locus. Twelve of the 22 fetuses at risk were male, ten were female. Seven of the 12 male fetuses were shown to be affected and were subsequently aborted. Four male fetuses appeared to be not affected. In one case, the diagnosis was made by use of an extragenic marker. The woman rejected fetal blood sampling to confirm the diagnosis. After birth, a normal factor VIII level was found in three of the four cases. The fourth pregnancy is still continuing. In one of the 12 male fetuses, no diagnosis at the gene level was possible. DNA analysis is expected to provide maximum certainty as to the phenotype of the fetus for approximately 60 per cent of the women; for another 37 per cent a rate of misdiagnosis of 4–5 per cent applies. In only 3 per cent of the cases will no diagnosis at the gene level be possible as yet. The new possibility of a prenatal diagnosis in the first trimester of pregnancy enabled some of these women to have a family of their own and was appreciated in particular by the women who underwent fetoscopy in an earlier pregnancy.     

Prenatal diagnostic testing for familial dysautonomia using linked genetic markers

Familial dysautonomia (FD), a recessively inherited disease, has been mapped to chromosome 9q31. Highly polymorphic dinucleotide repeat markers flanking the genetic locus and at the same genetic location have been identified. We describe the prenatal diagnosis of FD using linkage and linkage disequilibrium analyses with these markers. Twelve families were analysed for informativeness and of these, seven went on to have prenatal testing (a total of eight fetuses tested). All of these fetuses were predicted to be heterozygous unaffected (FD carriers). Seven fetuses have come to term and are normal. In the absence of a recombinant proband, a panel of three proximal and three distal markers is sufficient to provide informative flanking markers and an 87–96 per cent likelihood of a highly predictive test. In an additional family at 1:4 risk for FD, no DNA was available from the propositus. This family was analysed using linkage disequilibrium to the #18 allele of the tightly linked marker D9S58 in conjunction with linkage analysis using data from two unaffected children. Prenatal diagnosis in this family indicated an affected fetus.     

Prenatal diagnosis of severe combined immunodeficiency with defective synthesis of HLA molecules

The immunodeficiency associated with a defective expression of HLA molecules is an autosomal recessive disorder leading to death during childhood. We have performed prenatal diagnosis for six fetuses at risk for this disease by membrane immunofluorescence on blood lymphocytes and monocytes, using specific monoclonal antibodies for HLA class I and II molecules. Two pregnancies have been found to be affected. The diagnosis has been confirmed on each abortus by the study of the membrane expression of HLA class I and II molecules on blood lymphocytes and monocytes, and on thymic and splenic cells. The four other cases were found to be normal both during pregnancy and after birth. The detection of the defect as early as the 20th week of gestation allows selective termination.     

Conceiving a fetus for bone marrow donation: An ethical problem in prenatal diagnosis

We present a family who sought prenatal diagnosis in order to bear a healthy child to serve as an HLA–identical bone marrow donor for their son affected with Wiskott–Aldrich syndrome. They intended to abort HLA-incompatible fetuses who would have been unsuitable bone marrow donors. This case led us to conclude that prenatal diagnosis should not be used to benefit a third party or facilitate the conception or abortion of a fetus for the purpose of generating an organ for transplantation. The limits of parental autonomy and physician responsibility are discussed.     

Prenatal diagnosis of anhidrotic ectodermal dysplasia

This paper reports on successful prenatal diagnosis of X-linked anhidrotic ectodermal dysplasia (AED) by means of light and electron microscopy on fetal skin biopsies obtained under fetoscopy. In the present family two brothers of the proband were severely affected with the full symptomatology of AED, the pregnant female and her mother revealed minor symptoms with patches of skin lacking vellus hair. Control of lesional skin of the affected family members by electron microscopy revealed no ultrastructural abnormalities. However, all biopsies lacked skin appendages including hair follicles, sebaceous glands, and sweat glands. The lack of pilosebaceous follicles can be used as a diagnostic criterion since these structures are fully developed in normal fetuses of 20 weeks whereas the development of sweat glands does not start before week 20 to 24 of fetal life. Skin biopsies were taken from various regions of the fetus at risk via fetoscopy in week 20 and processed for light and electron microscopy. All samples revealed complete absence of all skin appendages in contrast to a total of 61 non-AED fetuses. Thus positive prenatal diagnosis of AED was made and the pregnancy was terminated. Control investigations after abortion confirmed the diagnosis.     

Fetal akinesia/hypokinesia sequence: Prenatal diagnosis and intra-familial variability

Intrauterine fetal movement plays a key role in normal embryonic and fetal development (Moessinger, 1983). When movement is absent or decreased, abnormal development takes place which can be appreciated in newborns and/or fetuses with the fetal akinesia/ hypokinesia sequence. This sequence is caused by a number of heterogeneous entities which result in decreased fetal movements by the action of intrinsic or extrinsic factors. Prenatal diagnosis of the akinesia/hypokinesia sequence may be possible during the second trimester through the use of real-time ultrasonographic evaluation of fetal movement. We report a family with three consecutive affected pregnancies in which the prenatal presentation of this sequence varied. Based on the phenotypic findings of the three affected fetuses, we believe that although they superficially resemble those features found in the New–Laxova syndrome, they are probably affected with a distinctly different lethal form of akinesia/ hypokinesia transmitted in an autosomal recessive fashion.     

Second trimester ultrasound screening for chromosomal abnormalities

The use of prenatal ultrasound has proven efficacious for the prenatal diagnosis of chromosomal abnormalities. The first sonographic sign of Down syndrome, the thickened nuchal fold, was first described in 1985. Since that time, multiple sonographically-identified markers have been described as associated with Down syndrome. The genetic sonogram, involving a detailed search for sonographic signs of aneuploidy, can be used to both identify fetuses at high risk for aneuploidy and, when normal, can be used to decrease the risk for aneuploidy for a pregnancy when no sonographic markers are identified. Combining the genetic sonogram with maternal serum screening may be the best method of assessing aneuploidy risk for women who desire such an assessment in the second trimester. Trisomy 18, Trisomy 13, and triploidy are typically associated with sonographically identified abnormalities and have a high prenatal detection rate. The use of the described sonographic signs in low-risk women requires further investigation, however, patients at increased risk for aneuploidy due to advanced maternal age or abnormal serum screening can benefit from a genetic sonogram screening for sonographic signs of aneuploidy to adjust their baseline risk of an affected fetus. Copyright © 2002 John Wiley & Sons, Ltd.     

Prenatal diagnosis of inborn errors in peroxisomal β-oxidation

In recent years, an increasing number of inherited diseases in man have been recognized in which there is an impairment in the peroxisomal β-oxidation of very-long-chain fatty acids. In general, these disorders are associated with severe neurological and physical abnormalities and death within the first years of life. In this paper we describe our experience with regard to the prenatal diagnosis of a number of different inborn errors of peroxisomal β-oxidation. Eleven pregnancies at risk were monitored by measuring very-long-chain fatty acid levels as well as very-long-chain fatty acid β-oxidation in cultured chorionic villous fibroblasts and/or amniotic fluid cells. Five affected fetuses were identified. It is concluded that prenatal diagnosis in this group of diseases can be done reliably using cultured chorionic villous fibroblasts or amniotic fluid cells.     

Prenatal diagnosis of congenital adrenal hyperplasia (21-OH deficiency type) by HLA typing

The close genetic linkage between HLA-B and congenital adrenal hyperplasia due to 21-hydroxylase deficiency permits prenatal diagnosis of an affected fetus by HLA typing of amniotic fluid cells in pregnancies at risk. Some families at risk, especially those with an affected girl with ambiguous genitalia, will only plan another pregnancy if a prenatal diagnosis is possible. After HLA typing of the index case, parents and eventually grandparents, the family were informed of the possibility of a prenatal diagnosis. Fibroblast cell lines were initiated from skin biopsies of the index cases and parents and were used as controls in the tests. HLA typing of the fetus was done on amniotic fluid cells grown in vitro using first, a microcytotoxicity test and second quantitative microabsorption test. Ten prenatal diagnoses are reported. In two cases the HLA genotype indicated an affected fetus, examination of the aborted fetuses was in agreement with the diagnosis. In one case an affected male fetus was diagnosed, the pregnancy is in progress. In seven cases an unaffected infant was predicted (four carriers and three homozygous normal infants).     

Prenatal diagnosis and carrier detection in mucopolysaccharidosis type II by mutation analysis. A 47,xxy male heterozygous for a missense point mutation

Identification of iduronate-2-sulphatase (IDS) gene mutations in patients with mucopolysaccharidosis type II (MPS II, Hunter syndrome) allows fast and reliable carrier detection and prenatal diagnosis. We describe here three cases of prenatal diagnosis by direct detection of the gene mutation. In addition to two affected male fetuses from two different families, a 47,XXY fetus carrying both the normal and the mutant allele was diagnosed in a third family. The latter pregnancy was carried to term and the child is obviously not affected by MPS II.     

Prenatal diagnosis of citrullinemia: Elevated levels of citrulline in the amniotic fluid in the three affected pregnancies

In three pregnancies at risk for citrullinemia affected fetuses were predicted both by strongly increased levels of citrulline in the amniotic fluid and by the reduced incorporation of ¹⁴C-citrulline into TCA-precipitable material in cultured amniotic fluid cells. The prenatal diagnoses of affected fetuses were confirmed after termination of the pregnancies by direct and indirect assays of argininosuccinate synthetase in the fetal livers and fibroblasts respectively. Measurement of the citrulline concentration in amniotic fluid appears to be a valuable adjunct in the prenatal diagnosis of citrullinemia.     

First-trimester prenatal diagnosis in twin pregnancies

Two twin pregnancies at risk for a sex-linked disorder are described. Both pregnancies were dichorionic. Transabdominal sampling was chosen for prenatal diagnosis. Molecular genetic techniques raised suspicion with regard to the accuracy of the samples in one case. Second-trimester amniocentesis confirmed the error. Selective feticide of the affected fetus was performed. When first-trimester prenatal diagnosis is offered in dichorionic twin pregnancies, confirmation through molecular genetic testing can confirm that villi have been obtained from different fetuses. All parties must be aware that additional invasive diagnostic procedures in the second trimester may be required in cases of doubt.     

Creatine kinase estimation in pure fetal blood samples for the prenatal diagnosis of duchenne muscular dystrophy

This paper compares the results of a survey of plasma creatine kinase (CK) activity measured in fetuses at-risk for Duchenne muscular dystrophy (DMD) with a reliable control series. Only pure fetal blood samples obtained by fetoscopy at between 17–24 weeks gestational age were used. Of the at-risk group 19 male pregnancies, mostly at low risk for DMD, proceeded to term with a normal outcome; there was no significant difference between their fetal plasma CK activities and the control group. Another 21 male pregnancies were terminated. This group included the highest risk mothers and hence was expected to contain a significant proportion of affected fetuses. The fetal plasma CK activity range was overlapping but significantly higher than the control group. No grossly elevated CK value was obtained. We conclude that, on average, DMD fetuses at this gestational age have higher plasma CK activity than controls. The problems of applying this finding to the prenatal diagnosis of DMD are discussed.     

Prenatal diagnosis of NADH:ubiquinone oxidoreductase deficiency

NADH:ubiquinone oxidoreductase (complex I of the mitochondrial respiratory chain) deficiency is a severe disorder with an often early fatal outcome. Prenatal diagnosis for complex I defects currently relies mainly on biochemical assays of complex I in fetal tissues such as chorionic villi (CV), and is only in a minority of cases possible by means of mutational analysis of nuclear-encoded genes of complex I. We report on our experience to date with prenatal diagnosis in pregnancies at risk for complex I deficiency. We measured complex I activity in native CV and/or cultured CV in 23 pregnancies in 15 families. In accordance with the results of the investigations in CV, 15 children were born clinically unaffected. Two prenatally diagnosed unaffected fetuses and two prenatally diagnosed affected fetuses were lost prematurely with spontaneous or provoked abortions, respectively. Two affected children were born (prenatally found to be affected). In two pregnancies a discrepancy between native and cultured cells was found. We conclude that prenatal diagnosis for complex I deficiency can be reliably performed. Pitfalls were encountered in using cultured CV as a result of maternal cell contamination (MCC). Future research on pathogenic nuclear mutations underlying complex I deficiency will extend the possibilities for prenatal diagnosis at the molecular level. Copyright © 2001 John Wiley & Sons, Ltd.