Trisomy 14 mosaicism leading to cytogenetic discrepancies in chorionic villi sampled at different times

Short- and long-term cultures of chorionic villi obtained in the 11th week of pregnancy revealed trisomy 14. After induced abortion trisomy 14 mosaicism was established in fetal skin and umbilical cord tissue while a second long-term culture of chorionic villi exhibited a normal karyotype. The results of the pathological investigations are discussed with respect to the cytogenetic findings.     

Resorbed co-twin as an explanation for discrepant chorionic villus results: Non-mosaic 47,XX, +16 in villi (direct and culture) with normal (46,XX) amniotic fluid and neonatal blood

Non-mosaic trisomy 16 was observed in chorionic villus cytotrophoblasts (direct) as well as cultured mesenchymal core cells derived from the pregnancy of a 38-year-old woman. Chromosome preparations from amniotic fluid and neonatal cultures (cord blood) were 46,XX. Normal fetal growth as determined by serial ultrasound examinations occurred throughout the pregnancy, which resulted in a healthy 2724 g female. Multiple biopsies taken from the umbilical cord, placental cotyledons, and fetal membranes were 46,XX. However, a placental nodule and three of six cultures initiated from membranes (amnion and chorion) showed 46,XX/47,XX, + 16 mosaicism. We propose that the trisomy 16 cells arose from residual villi derived from a trisomic cotwin that never developed. This case further demonstrates that normal fetal growth may presage normal outcome irrespective of cytogenetic findings in cytotrophoblasts (direct) and cultured mesenchymal core cells.     

Follow-up of pregnancies complicated by placental mosaicism diagnosed by chorionic villus sampling

Thirty-nine (2.3 per cent) of 1724 chromosome studies from diagnostic chorionic villus samplings (CVS) done between 1983 and 1990 showed either level III (true) mosaicism (1.2 per cent) or level II (pseudo-) mosaicism (1.1 per cent) for chromosomal aneuploidy. Follow-up information on these 39 pregnancies was collected from questionnaires to families, paediatricians, and obstetricians. For all cases in which the pregnancy was continued and further testing was accomplished, the mosaicism was felt to be confined to the placenta. As compared with a control group of pregnancies evaluated by CVS with normal karyotypes, there was no increased incidence of pregnancy loss, congenital malformations, or developmental delay in the infants. Although intrauterine growth retardation occurred in several of the level III mosaic cases, adequate catch-up growth has been demonstrated.     

The dilemma of chromosomal mosaicism in chorionic villus sampling—‘direct’ versus long-term cultures

Chromosomal mosaicism is one of several unanswered dilemmas in first-trimester prenatal diagnosis. We report the course of a pregnancy in which a normal karyotype was detected on direct CVS preparation and fetal blood, 100 per cent trisomy 21 in one long-term CVS culture, and low-rate trisomy 21 mosaicism in a second long-term CVS culture and amniocentesis. The phenotypically normal infant had a 6 per cent mosaicism of trisomy 21. It appears that a persistent low-rate mosaicism in different tissues may be indicative of the true status of the fetus.     

Trisomy 18 in chorionic villus sampling: Problems and consequences

Among 1547 patients undergoing first-trimester prenatal diagnosis, 100 fetal chromosome aberrations were detected. Thirteen of these involved chromosome 18. In two structural abnormalities of chromosome 18, the aberration could be excluded in amniotic fluid cells and two healthy infants were born. Trisomy 18 was not confirmed in amniotic fluid cells in three trisomy 18 mosaics. In eight non-mosaic trisomy 18 first-trimester diagnoses, the diagnosis was excluded by amniotic fluid cells or fetal cultures in four, and confirmed in the remaining four. Diagnosis of chromosome 18 aberrations in the direct preparation should be confirmed in the long-term culture of the chorionic villus sample or by amniotic fluid cultures.     

Chromosome mosaicism and maternal cell contamination in chorionic villi

While chorionic villus sampling allows both early and rapid prenatal diagnosis of chromosome disorders, the accuracy of this technique has not been fully established. Maternal cell contamination and pseudomosaicism represent two major sources of diagnostic error. Combined use of both direct chromosome preparations and villus cultures is important in overcoming these problems. Direct preparations of villus tissue allow recognition of maternal cell contamination of villus cultures. Conversely, villus cultures yield higher resolution chromosomes and may be helpful in differentiating between true versus pseudomosaicism when two or more cell lines are identified in direct chromosome preparations. Preliminary data suggest that analysis of direct preparations from multiple individually processed villus fragments may also be of value in this regard. Until more experience is gained, mid-trimester amniocentesis should be offered to CVS patients when mosaicism is encountered.     

Unusual segregation for 11q;22q parental translocation in a triplet pregnancy: Prenatal diagnosis in chorionic villi and amniotic fluid

The prenatal diagnosis of an 11q;22q translocation in a triplet pregnancy detected at the time of chorionic villus sampling (CVS) because of advanced maternal age is reported. Karyo-types obtained from two apparently different CV samples showed the balanced form of translocation, while the one obtained from a third empty sac showed the unbalanced form: 46, XX, −22, + der(22)t(11;22). Second-trimester amniocentesis confirmed the balanced translocation in one of the two viable fetuses and a normal karyotype in the other. The detected karyotypes derived from two different types of meiotic segregation, alternate and adjacent 1. To our knowledge, this is the first reported case of an unbalanced karyotype not due to a 3:1 meiotic segregation of this specific translocation.     

Maternal cell contamination in cultured chorionic villi: Comparison of chromosome Q-polymorphisms derived from villi,fetal skin,and maternal lymphocytes

Maternal cell contamination of chorionic villi (CV) samples used for first trimester prenatal diagnosis can cause obvious and/or unrecognized diagnostic dilemmas. The purpose of this investigation is to assess the frequency of maternal cell contamination (MCC) in chorionic villus samples and to evaluate selected parameters which might predict where contamination is more likely to have occurred. Maternal lymphocytes, chorionic villi from ultrasonically directed transcervical catheter aspiration, and fetal tissue were obtained at 8–11 weeks gestation from 45 patients undergoing elective termination. Quinacrine (Q) banded metaphases were compared from duplicate direct preparations of chorionic villi; cultured chorionic villi, fetal fibroblast tissue cultures, and maternal lymphocyte cultures. Q-polymorphisms in metaphase chromosomes were 100 per cent concordant between fetal tissue and direct CV preparation. However, evidence for maternal cell contamination occurred in 13.1 per cent of cultured chorionic villi preparations where polymorphisms were found to be identical between maternal and cultured CV and both distinct from fetal tissue preparations. Where MCC was identified, it was noted that CV cell cultivation interval was prolonged (24.2±6.8 days) compared with non-contaminated cultures (14.1±4.4 days) (p <0.05). We conclude that maternal cell contamination is a significant problem with chorionic villus sampling. Where direct preparations are not employed or when cultures are ‘slow growing’, MCC may be a significant and unrecognized complication re: fetal diagnosis. Direct preparations, multiple cultures, quinacrine banding, and maternal Q-polymorphism comparisons can minimize diagnostic dilemmas secondary to maternal cell contamination. Q-polymorphism comparisons between maternal and fetal chromosomes should be included in all instances where cultured chorionic villi are utilized for fetal diagnosis and where direct preparations are not available.     

Apparent non-mosaic trisomy 16 in chorionic villi: Diagnostic dilemma or clinically significant finding?

A case is presented in which apparent non-mosaic trisomy 16 was found in chorionic villi (direct and culture) obtained from a patient undergoing first-trimester prenatal diagnosis. The fetal karyotype subsequently was determined to be 46,XX by follow-up amniocentesis. Serial ultrasonographic examinations revealed placental sonolucencies and intrauterine growth retardation. At 37 weeks, a small-for-gestational-age female was delivered by Caesarean section for fetal distress. Postnatal cytogenetic studies revealed a normal female karyotype in cord blood and mosaic trisomy 16 in plaental tissues. These findings suggest that in cases where aneuploidy is confined to placental tissues, it may have biological significance, as evidenced by the apparent placental dysfunction and poor fetal growth in this case.     

Postnatal placental confirmation of trisomy 2 and trisomy 16 detected at chorionic villus sampling: A possible association with intrauterine growth retardation and elevated maternal serum alpha-fetoprotein

Detection of trisomy 2 and trisomy 16 mosaicism through chorionic villus sampling (CVS) is not an infrequent finding. We describe here two cases, one of non-mosaic trisomy 2 and the other of high level mosaicism for trisorny 16. Amniocentesis in both cases demonstrated non-mosaic 46,XY karyotypes. Each pregnancy continued to delivery of liveborn, normal-appearing boys; both pregnancies were complicated by severe intrauterine growth retardation (IUGR). Postnatal studies of placental biopsies in both cases confirmed the original CVS findings, whereas cord blood karyotypes were normal in both boys. Both children have demonstrated adequate catch-up growth.     

Prenatal diagnosis by chorionic villus sampling: Lessons of the first 600 cases

Chorionic villus sampling (CVS) has emerged as a first trimester alternative to amniocentesis for the prenatal detection of genetic disorders. We report our experience in 600 consecutive CVS procedures to better delineate the safety, efficacy and reliability of this new method of prenatal diagnosis. Adequate samples were obtained at the initial visit in 97 per cent of the cases, and successful cultures were established in 98.7 per cent of these patients. Chromosome abnormalities were detected in 5.9 per cent of those pregnancies tested because of advanced maternal age (≥ 35 years). A discrepancy between the villus karyotype and that of the fetus was found in 2.0 per cent of cases, and most commonly consisted of mosaicism in the villus sample for a chromosomal abnormality that was not found in fetal samples. The risk of spontaneous abortion following the procedure was 6.3 per cent. We conclude that chorionic villus sampling is an acceptably safe and reliable procedure, but further investigation is needed before it can become an established technique in prenatal diagnosis.     

The European collaborative study on mosaicism in chorionic villus sampling: Data from 1986 to 1987

Data on a total of 11 855 diagnostic chorionic villus samples obtained in the years 1986 and 1987 were compiled from a questionnaire filled in by 36 European cytogenetic centres. Mosaicism was reported in 141 cases. The cytogenetic findings were followed by induced abortion in 24 cases. Spontaneous abortion was observed in nine mosaic pregnancies, a rate not significantly different from that observed for CVS in total. Mosaicism was found in 1.2 per cent of analyses by direct analysis/short-term culture, in contrast to the 0.6 per cent found after long-term culture. Evidence for fetal non-mosaicism was found in 99 of the 141 cases. The finding of mosaicism in first-trimester CVS should always elicit further analyses, preferably after amniocentesis, to substantiate the suspected fetal chromosome aberration.     

Transabdominal chorionic villus sampling for fetal genetic diagnosis. Technical and obstetrical evaluation of 100 cases

First trimester fetal diagnosis was established in 100 pregnancies at risk by transabdominal chorionic villus sampling (TA-CVS). Forty-eight per cent of the women were 35 years or more at the time of sampling. Using the double needle technique, both the aspiration and the diagnostic success rate were 100 per cent. The mean amount of villi aspirated was 28·2 mg (10–50 mg). The mean needle time was 3 min. Vaginal spotting appeared in 2 per cent of the women. Four women had therapeutic abortion due to abnormal findings and one for social reasons. Three fetuses with normal karyotypes were lost. Excluding the therapeutic abortions, the fetal loss rate was 3±2 per cent. The fetal loss rate in the amniocentesis control group (n = 200) was 3±6 per cent. The cytogenetic diagnosis was carried out by the direct preparation technique as well as by chorion villus cultivation. All karyotypes were confirmed by lymphocyte cultures from umbilical cord blood or heel blood from the newborn or from aborted fetal tissue. Transabdominal CVS is deemed a safe and easy tool for achieving chorionic villi in the first trimester.     

Trisomy 8 mosaicism in chorionic villus sampling: Case report and counselling issues

We report an unusual case involving chorionic villus sampling (CVS) and trisomy 8 mosaicism. CVS showed a normal direct preparation while the culture showed mosaicism for trisomy 8. Subsequent amniocentesis revealed only normal chromosomes. A peripheral blood culture after birth revealed low-level trisomy 8 mosaicism. The patient appeared phenotypically and developmentally normal at 30 months of age. We conclude that prenatal counselling for similar cases needs to include the rare but real possibility that chromosome mosaicism detected prenatally may be found postnatally with largely unknown consequences. Secondly, low-level chromosomal mosaicism may be more common than previously recognized. Thirdly, very low-level trisomy 8 mosaicism may be compatible with a normal phenotype but long-term follow-up is required. And lastly, the use of fetal blood sampling is questionable in these cases because the phenotype may not be accurately predicted. Further studies of such cases are needed to address these important and unanswered issues, including the potential implication of mosaicism on academic performance and cognitive functioning.     

First-trimester biochemical and molecular diagnoses using chorionic villi: High accuracy in the U.S. collaborative study

The accuracy of biochemical and molecular prenatal diagnoses using chorionic villi as the fetal source was assessed by seven centres participating in the NICHD collaborative study on the safety and accuracy of chorionic villus sampling (CVS) and amniocentesis. Of 601 pregnancies studied, biochemical methods were used to determine the diagnosis in 283 fetuses at risk for 35 different metabolic disorders. Fifteen different lysosomal storage diseases accounted for 81 per cent of the biochemical prenatal diagnoses performed, with 57 per cent of these pregnancies at risk for Tay-Sachs disease. No errors were made in the biochemical diagnoses that predicted affected or unaffected fetuses. However, the diagnoses of certain disorders (e.g., mucopolysacchariodosis type IH, metachromatic leukodystrophy, and Krabbe disease) occasionally required confirmatory studies in cultured amniocytes because the enzyme results were inconclusive in direct and/or cultured villi or due to the presence of a pseudodeficiency allele. Of these, only the diagnosis of a fetus at risk for Krabbe disease remained inconclusive after special studies to discriminate between mutant and pseudodeficiency alleles. Recombinant DNA techniques were used to predict the diagnosis of 318 fetuses at risk for 16 different disorders in which the defective disease gene could be detected either directly or by linkage analysis to a nearby polymorphic marker. Of these, 32 per cent were for haemoglobinopathies, 25 per cent for cystic fibrosis, 24 per cent for Duchenne or Becker muscular dystrophy, and 7 per cent for haemophilias. Pregnancies at risk for known disorders with specific molecular lesions (e.g., sickle cell disease) were accurately diagnosed in direct and/or cultured villi. Diagnoses requiring analyses with closely linked polymorphic markers were occasionally uninformative or inconclusive. Maternal contamination was not reported in any biochemical or molecular-based diagnosis. These studies document the high accuracy and rapidity of both biochemical and mutation-specific prenatal diagnoses with direct and cultured chorionic villi.     

Lack of sampling site variation in chorion villus biopsy as assessed by DNA,enzymatic, morphological and cytogenetical analyses

A study of villus samples from eight random sites on five electively aborted chorion sacs was performed to determine any significant differences in yield, quality and composition of DNA, iduronate sulphate sulphatase activity and karyoptype status. The villi were also examined for their histological characteristics (e.g. stem, intermediate or terminal villi) and for HCG and BGP immuno-reactivities. The overall findings indicated no significant site to site variations in any of the parameters studied. It is therefore proposed that any villus should be equally suitable for prenatal diagnosis.     

Prenatal diagnosis of chinese homozygous α-thalassaemia 1 and haemoglobin H disease by analysis of α- and φζ-globin genes in chorionic villi and amniocytes

Eighty-eight high-risk pregnancies, 81 for homozygous α-thalassaemia 1 and 7 for haemoglobin (Hb) H disease, were collected in this study. Chorionic villus sampling (CVS) was done in 63 cases and amniocentesis in 25 cases to obtain fetal cells. Southern blotting and DNA hybridization with α- and φζ-globin gene probes were used to determine the α-globin gene status. In two non-informative families with non-deletional mutations, DNA analysis failed to rule out the affected condition, and fetal blood sampling (FBS) and Hb electrophoresis were used for the final diagnosis. In the 81 fetuses at risk for homozygous α-thalassaemia 1, 17 (13 by CVS and 4 by amniocentesis) were afffected, 30 were α-thalassaemia 1 heterozygotes, 19 were normal, and the remaining 15 were either normal or heterozygous. In the seven fetuses at risk for Hb H disease, one was normal, three were α-thalassaemia 1 heterozygotes, two were α-thalassaemia 2 heterozygotes, and one was affected with Hb H disease and developed hydrops fetalis. DNA analysis on fetal cells enabled us to diagnose prenatally severe α-thalassaemias, to prevent the birth of infants with Hb H disease, and to minimize maternal obstetrical complications from harbouring a fetus with Hb Bart's hydrops fetalis.     

Direct preparations from chorionic villi–relationship between villous morphology and mitotic index

It has been postulated that chorionic villi with abundant sprouts have a higher mitotic index and are therefore preferable for obtaining direct chromosome preparations from chorionic villus samples. This theory was tested by correlating villous morphology with mitotic index. Surprisingly, no statistically significant relationship was found. Choice of culture medium, however, was found to be important, with serum-free RPMI yielding a higher mitotic index than 40 per cent FCS in MEM. We conclude that villous morphology, as assessed in this study, is not a major factor in determining the success of direct chromosome preparations.     

Follow-up and pregnancy outcome after a diagnosis of mosaicism in CVS

In 2103 consecutive diagnostic chorionic villus samples, examined in a 4-year period in our clinical genetics unit, 26 samples (1.2 per cent) presented chromosomal mosaicism in the direct and/or long-term culture preparations. Only once (46,XX/47,XX,+9) was the mosaicism confirmed in the fetus. In the cytogenetic follow-up studies of the remaining 25 pregnancies, in no cases could the aberration be confirmed in amniotic fluid or fetal tissue. One patient requested a termination after the CVS result. Of the remaining 24 pregnancies, four (16.7 per cent) ended in a spontaneous abortion. These findings suggest an association between placental mosaicism and fetal loss.