European collaborative study on prenatal diagnosis: mosaicism, pseudomosaicism and single abnormal cells in amniotic fluid cell cultures

Comparison of chromosomal instability of human amniocytes in primary and long-term cultures in AmnioMAX II and DMEM media: A cross-sectional study

Background

The genomic stability of stem cells to be used in cell therapy and other clinical applications is absolutely critical. In this regard, the relationship between in vitro expansion and the chromosomal instability (CIN), especially in human amniotic fluid cells (hAFCs) has not yet been completely elucidated.

Objective

To investigate the CIN of hAFCs in primary and long-term cultures and two different culture mediums.

Materials and Methods

After completing prenatal genetic diagnoses (PND) using karyotype technique and chromosomal analysis, a total of 15 samples of hAFCs from 650 samples were randomly selected and cultured in two different mediums as AmnioMAX II and DMEM. Then, proliferative cells were fixed on the slide to be used in standard chromosome G-banding analysis. Also, the senescent cells were screened for aneuploidy considering 8 chromosomes by FISH technique using two probe sets including PID I (X-13-18-21) & PID II (Y-15-16-22).

Results

Karyotype and interphase fluorescence in situ hybridization (iFISH) results from 650 patients who were referred for prenatal genetic diagnosis showed that only 6 out of them had culture- derived CIN as polyploidy, including mosaic diploid-triploid and diploid-tetraploid. Moreover, the investigation of aneuploidies in senesced hAFCs demonstrated the rate of total chromosomal abnormalities as 4.3% and 9.9% in AmnioMAX- and DMEM-cultured hAFCs, respectively.

Conclusion

hAFCs showed a low rate of CIN in two AmnioMAX II and DMEM mediums and also in the proliferative and senescent phases. Therefore, they could be considered as an attractive stem cell source with therapeutic potential in regenerative medicine.

Prenatal diagnosis of mosaic trisomy 2 and literature review

Background

We presented two cases of mosaic trisomy 2 with high risk of maternal serum screening and non-invasive prenatal testing (NIPT). The invasive amniocentesis was performed and genetic tests including karyotype, single nucleotide polymorphism array(SNP-array), interphase fluorescence in situ hybridization (FISH) were employed to detect the chromosomal abnormality.

Results

Cytogentic analysis of the case 1 and 2 showed a mosaic karyotype consisting of two cell lines (mos 47,XY,+2[8]/46,XY[19] and mos 47,XX,+2[7]/46,XX[28], respectively). SNP-array using DNA extracted from uncultured amniotic fluid cells revealed a result of arr[GRCh38](2)x2~3, which indicated that chromosome 2 may be trisomy of mosaicism in both two cases. The results of interphases FISH confirmation test showed that three red signals of the CEP 2 specific probe in 14%(14/100) and 12%(12/100) of the two cases’ cells, respectively, which indicated a mosaicism for trisomy 2 in the uncultured amniocytes. Fetal ultrasound of case 1 suggested that the long bone is smaller than the gestational age, while the case 2 showed that the biparietal diameter (BPD), head circumference (HC) and femur length (FL) were smaller than gestational age along with abnormal cardiac structure.

Conclusions

We presented two cases with mosaic trisomy 2 and performed confirmatory genetic testing using cultured and uncultured amniocytes. When maternal serum screening and NIPT suggesting high risk, genetic counselor should be alert for increasing possibility of chromosomal anomalies if combined with abnormal ultrasound findings.

Higher male prevalence of chromosomal mosaicism detected by amniocentesis

OBJECTIVE

To present the calculated frequencies, male to female sex-ratio, and modes of ascertainments in different levels of chromosomal mosaicism (CM) detected at amniocentesis.

MATERIALS AND METHODS

This's a 10-years retrospective study between January 2008 and December 2017 and there were 13,752 cases of amniocentesis performed in MacKay Memorial Hospital, Taipei, Taiwan. Eight hundred and thirty four cases of CM were collected in this study. We reviewed their types of chromosomal abnormalities of mosaicism, the modes of ascertainment (including: advanced maternal age, abnormal ultrasound findings, abnormal maternal serum screening result, and other reasons), maternal age, gestational age at amniocentesis, fetal gender, and perinatal findings. After amniocentesis, in situ culture was performed and the results of karyotype with CM were divided in to three levels.

RESULTS

In our sample of 13,752 amniocentesis, 834 cases with all levels of CM were collected in this study. Of them, there were 562 cases (4.09%) with level I mosaicism, 207 cases (1.51%) of level II mosaicism, and 65 cases (0.47%) of level III mosaicism (Table 1). In the group of advanced of maternal age (AMA), their calculated frequencies, 4.18% in level I, 1.46% in level II and 0.41% in level III, were very similar to those in total cases (p value = 0.206) without statistical significance. In the group of abnormal ultrasound findings, the calculated frequency was much higher in level III (0.87%), however, there was no statistical significance because of the small numbers of level III. In our cases of amniocentesis, the case numbers of male case (50.20%) is very similar to female (49.80%), and the male to female ratio was 1.01. But, we found more cases of male with CM (444 cases) than female (390 cases). The sex-ratio in different levels' calculated frequencies of CM showed similar in level I, and male prevalence was found in level II and III with statistical significance (p value = 0.022). The male prevalence also revealed in both numerical and structural abnormalities in level II and level III, but no difference in the cases of level I.

CONCLUSION

In conclusion, our observation showed a novel finding of higher male prevalence of CM in level II and III, and both in numerical and structural abnormalities. It's consistent with the theory of better survival in male embryo after partial self-correction of initial chromosomal aberrations, male-specific selection against chromosomal abnormalities.

Case of non-mosaic trisomy 20 in amniotic fluid cultures without anomalies in the fetus: cytogenetic discrepancy between amniocytes and fetal blood

We report a case of non-mosaic trisomy 20 detected prenatally by amniocentesis during the 16th week of pregnancy. Fetal blood sampling showed a normal karyotype and no fetal, neonatal or infant abnormalities were observed. Amniotic fluid cell karyotyping revealed a trisomy 20 (47,XY,+20) with 100% trisomic cells (38/38); however, a subsequent cordocentesis revealed a normal male karyotype. Moreover, a follow-up ultrasonographic examination did not reveal any major congenital malformations, and a healthy male infant was delivered subsequently at an appropriate gestational age without obvious anomalies. Cytogenetic analysis of blood lymphocytes from the infant revealed a normal karyotype, but cultured cells from the term placenta showed a mosaic karyotype 47,XY,+20/46,XY with 88% trisomic cells (44 of 50). Furthermore, no anomalies or developmental delays were observed in the neonatal period, thus suggesting two possibilities: confined placental mosaicism with the presence of normal and abnormal cell lineages, or generalized mosaicism affecting a limited number of tissues in both the placenta and fetus.

The application of an in situ karyotyping technique for mesenchymal stromal cells: a validation and comparison study with classical G-banding

The cytogenetic analysis of mesenchymal stromal cells (MSCs) is essential for verifying the safety and stability of MSCs. An in situ technique, which uses cells grown on coverslips for karyotyping and minimizes cell manipulation, is the standard protocol for the chromosome analysis of amniotic fluids. Therefore, we applied the in situ karyotyping technique in MSCs and compared the quality of metaphases and karyotyping results with classical G-banding and chromosomal abnormalities with fluorescence in situ hybridization (FISH). Human adipose- and umbilical cord-derived MSC cell lines (American Type Culture Collection PCS-500-011, PCS-500-010) were used for evaluation. The quality of metaphases was assessed by analyzing the chromosome numbers in each metaphase, the overlaps of chromosomes and the mean length of chromosome 1. FISH was performed in the interphase nuclei of MSCs for 6q, 7q and 17q abnormalities and for the enumeration of chromosomes via oligo-FISH in adipose-derived MSCs. The number of chromosomes in each metaphase was more variable in classical G-banding. The overlap of chromosomes and the mean length of chromosome 1 as observed via in situ karyotyping were comparable to those of classical G-banding (P=0.218 and 0.674, respectively). Classical G-banding and in situ karyotyping by two personnel showed normal karyotypes for both cell lines in five passages. No numerical or structural chromosomal abnormalities were found by the interphase-FISH. In situ karyotyping showed equivalent karyotype results, and the quality of the metaphases was not inferior to classical G-banding. Thus, in situ karyotyping with minimized cell manipulation and the use of less cells would be useful for karyotyping MSCs.

Prenatal diagnosis and genetic counseling for mosaic trisomy 13

Counseling parents of a fetus with trisomy 13 mosaicism remains difficult because of the phenotypic variability associated with the condition; some patients exhibit the typical phenotype of complete trisomy 13 with neonatal death, while others have few dysmorphic features and prolonged survival. This article provides a comprehensive review of the prenatal diagnosis and genetic counseling for mosaic trisomy 13, including confined placental mosaicism 13, mosaic trisomy 13 diagnosed at amniocentesis, and phylloid hypomelanosis in association with mosaic trisomy 13.

Non-mosaic trisomy 20 of paternal origin in chorionic villus and amniotic fluid also detected in fetal blood and other tissues

Trisomy 20 mosaicism is a common abnormality found in prenatal diagnosis. Its clinical significance remains unclear since approximately 90-93% of cases result in normal phenotype. Only 5 cases of non-mosaic trisomy 20 in amniotic fluid culture surviving beyond the first trimester have been reported. Moreover, trisomic cells are generally not detectable in blood and have only been reported in three cases. We present a case of non-mosaic trisomy 20 found in chorionic villi sample and amniotic fluid culture in a fetus with minor abnormalities not detected by ultrasound examination. Pathological examination of the fetus only revealed right pulmonary isomerism and camptodactily, and no major malformations were disclosed. Trisomic lineage was also detected in fetal blood, kidney, skin and brain tissue cultures. Molecular analysis revealed that the extra chromosome 20 was originated in paternal meiosis. To our knowledge, we report the first prenatal case of non-mosaic trisomy 20 of paternal origin that has been confirmed in several fetal tissues, including blood, in a fetus with minor malformations not detected prenatally.

Expanding the phenotype of mosaic trisomy 20

Mosaic trisomy 20 is one of the more common cytogenetic abnormalities found on amniocentesis or chorionic villus sampling. Studies have shown that outcome is normal in 90-93% of prenatally diagnosed cases. There are however, reports in the literature of children with mosaic trisomy 20 described as having an assortment of dysmorphic features and varying levels of developmental delay. Unfortunately, the literature has not defined a specific phenotype for this entity. Here we report on three patients with mosaic trisomy 20, two of whom were identified prenatally. Over a number of years of follow-up it has become apparent that there are some striking similarities among the three. Comparison between our patients and the literature cases indicates a more consistent phenotype than has previously been suggested. Recurring features include; spinal abnormalities (including spinal stenosis, vertebral fusion, and kyphosis), hypotonia, lifelong constipation, sloped shoulders, and significant learning disabilities despite normal intelligence. These findings may be overlooked on routine history and physical exam or assumed to be standard pediatric problems. It is not our intention to suggest that there is a distinctive face for this entity but to suggest that a subtle phenotype does exist. We have attempted to identify a set of findings for which any child diagnosed with mosaic trisomy 20 should be assessed or followed even in the presence of an apparently normal physical exam at birth.

Prenatal diagnosis of mosaicism for 11q terminal deletion

The phenotype of 11q terminal deletion also known as Jacobsen syndrome is a clinically well known entity whose diagnosis in infancy and childhood is based on clinical examination, hematological and cytogenetic findings. Hematological features in Jacobsen syndrome are very similar to those reported in Paris-Trousseau syndrome (PTS) which is also associated with11q terminal deletion. Karyotype analysis shows a variable terminal deletion from 11q23 sub-band extending to the telomere. Most often in patients with Jacobsen syndrome, this chromosomal deletion is present in all metaphases. We report on the identification of a distal 11q deletion in mosaic (20% of deleted cells) in a fetus ascertained after amniocentesis for maternal serum screening test indicative for Down syndrome. The present case is the third prenatal diagnosis of a mosaic for a distal 11q deletion with the lowest mosaicism rate. The 2D-ultrasound examination and cord blood hematological studies were useful to estimate the prognosis at term, considering the contribution of the mosaicism rate to the phenotypic variability in Jacobsen syndrome. The identification of mosaicism for distal 11q deletion is a very rare event in prenatal diagnosis. This case illustrates the complexity in genetic counselling for prenatally ascertained partial monosomy 11qter in mosaic.

Detection of mosaicism for primary trisomies in prenatal samples by QF-PCR and karyotype analysis

OBJECTIVES

QF-PCR can be used to rapidly diagnose primary trisomy in prenatal samples. Our objectives were to estimate the prevalence of primary trisomy mosaicism for chromosomes 13, 18 or 21 in a cohort of prenatal samples, and to compare and contrast the detection of this mosaicism using both QF-PCR and karyotype analysis.

METHODS

Data was collated from all prenatal samples displaying mosaicism for a primary trisomy between June 2000 and March 2004. Levels of mosaicism were estimated and samples were categorised according to the cell population in which the mosaicism was detected.

RESULTS

In a total of 8983 samples, 18 samples (0.20%) displaying mosaicism were detected, including trisomy 13 (three samples), trisomy 18 (seven samples), trisomy 21 (seven samples) and mosaic triploidy (one sample). This included 7 amniotic fluid and 11 chorionic villus samples. Mosaicism was detected by QF-PCR in 12 samples and by karyotype analysis in 8 samples.

CONCLUSIONS

QF-PCR can detect mosaicism when the abnormal cell line contributes at least 15% of the whole sample. Use of both karyotype and QF-PCR analysis leads to the detection of more cases of mosaicism than either test alone.

Prenatal diagnosis, sonographic findings and molecular genetic analysis of a 46,XX/46,XY true hermaphrodite chimera

OBJECTIVES

To present the prenatal diagnosis, sonographic findings and, molecular genetic analysis of a 46,XX/46,XY true hermaphrodite chimera and to review the literature.

CLINICAL SUBJECT AND METHODS

Amniocentesis was performed at 22 weeks' gestation because of sonographic diagnosis of ambiguous genitalia. Initial amniocentesis, repeat amniocentesis, and cordocentesis revealed a mixture of 46,XX cells and 46,XY cells. Polymorphic DNA marker analysis using the fetal and parental blood was applied to investigate the genetic origin of the chimera. A 3,625-g baby was delivered at 37 weeks' gestation with clitoromegaly, prominent labia majora, fusion of the labia, and an orifice of the urogenital sinus. A lymphangioma was noted over the right arm and was excised at age 3 days. Extraembryonic tissues and the infant's skin were cytogenetically and molecularly studied.

RESULTS

Initial amniocentesis, repeat amniocentesis, and cordocentesis revealed the karyotype of 46,XX[12]/46,XY[9], 46,XX[15]/46,XY[12], and 46,XX[27]/46,XY[15], respectively. The cytogenetic results of the extraembryonic tissues and skin were consistent with prenatal diagnosis. Informative sex chromosome and pericentromeric autosome markers demonstrated double paternal and single maternal genetic contributions.

CONCLUSIONS

Prenatal sonographic diagnosis of ambiguous genitalia should alert true hermaphroditism and prompt thorough genetic investigations. DNA marker analysis is helpful in delineation of true fetal chimerism as well as determination of its genetic origin in prenatally detected 46,XX/46,XY chromosome complement.

Maternal cell contamination of prenatal samples assessed by QF-PCR genotyping

OBJECTIVES

To establish the genotype of cultured cells from a cohort of amniotic fluid and chorionic villus samples, and compare this genotype with that obtained from uncultured material from the same sample, in order to assess the frequency and significance of maternal cell contamination of prenatal samples.

METHODS

Quantitative fluorescence-polymerase chain reaction (QF-PCR) was carried out by amplification of microsatellite markers using fluorescence-labelled primers, followed by quantitative analysis of the allele peaks on a genetic analyser. A multiplex of 12 primer pairs for four loci on each of chromosomes 13, 18 and 21 was used.

RESULTS

A total of 307 prenatal samples were tested. Of the 254 amniotic fluid samples, 39.8% had some degree of bloodstaining, ranging from 5% bloodstaining in the cell pellet to heavily bloodstained fluid. Uncultured samples were tested by QF-PCR analysis and the cultured cells were tested by both QF-PCR and karyotype analysis. Of the samples, 90.2% had the same single genotype on direct and cultured material. Two samples (0.65%) were mosaic for an aneuploidy cell line. A second genotype, interpreted as maternal cell contamination, was identified in direct and/or cultured preparations in 9.1% of samples, 17.8% of which were not bloodstained. Seven amniotic fluid samples (2.8%) showed maternal cell contamination in cultured material.

CONCLUSIONS

For heavily bloodstained amniotic fluid samples, a maternal blood specimen may help interpret the results of rapid trisomy testing, followed by confirmation of the fetal origin of cultured cells. QF-PCR analysis has established a higher incidence of maternal cell contamination of cultured amniocytes than previous reports; the presence of MCC (maternal cell contamination) in cultured cells from samples with no bloodstaining underlines the need for karyotype analysis of more than one XX culture.

Clinical proceduress in prenatal diagnosis

The prenatal diagnosis of fetal genetic disease has become a routine part of obstetric care. Pregnancies at risk are identified by a number of factors, including maternal age, positive serum screening, a history of a previous affected child, a parental chromosome rearrangement or an ultrasound-identified anomaly. Invasive diagnostic testing can be performed in the first trimester by chorionic villus sampling or in the second trimester by amniocentesis. Both procedures are safe, with an equivalent 0.5% risk of procedure-induced pregnancy loss. When performed prior to the routine sampling window of 15 weeks, amniocentesis may increase the risk of talipes equinovarus, the highest risk being encountered prior to 13 weeks' gestation. When chorionic villus sampling is performed prior to 9 weeks' gestation, there may be an increased risk of limb reduction defects. The laboratory analysis of both procedures is reliable. Chorionic villus sampling has a 1-2% incidence of confined placental mosaicism, requiring additional evaluation in some cases.

Prenatal detection of the 17p11.2 duplication in Charcot-Marie-Tooth disease type 1A: necessity of a multidisciplinary approach for heterogeneous disorders

Charcot-Marie-Tooth (CMT) disease is a typical example of a clinically and genetically heterogeneous disorder and, in most cases, is dominantly inherited and caused by a 1.5 megabase duplication on chromosome 17p11.2 containing the PMP22 gene. This is a non-lethal disease with a wide spectrum of severity, from asymptomatism to severe motor and sensory disability. Unpredictable degree of disability is usually the reason why prenatal diagnosis is required and must be addressed. Molecular procedures such as the use of polymorphic non microsatellite STRs, allowing very fast and reliable results even when requiring a gene dosage interpretation are now available and have been recently validated in post-natal diagnosis. Our results indicate that this approach is also the best-adapted method in case of prenatal diagnosis. Nevertheless, ethical considerations raised by prenatal diagnosis in CMT and more generally in non-lethal disorders remain to be actively considered. Here, we present our experience in genetic counselling, and address the psychological issues for 7 CMT at risk pregnancies. In five cases, a CMT1A duplication was evidenced; pregnancy was terminated in four of these cases and the parents from one affected foetus decided to pursue the pregnancy.

A case of maternal uniparental disomy of chromosome 9 diagnosed prenatally and the related problem of residual trisomy

Non-mosaic trisomy 9 was found in a chorionic villus (CV) sample taken from a 43-year-old woman referred for prenatal chromosome analysis due to advanced maternal age. Follow-up amniocentesis revealed level 2 mosaicism for trisomy 9. Trisomy 9 was not detected at fetal blood sampling. Molecular analysis of fetal (amniocyte) DNA showed maternal uniparental heterodisomy (UPD) for chromosome 9. Two crossovers resulted in a region of isodisomy in the distal long arm. Trisomy rescue of a meiosis 1 segregation error seems to have been responsible for the uniparental disomy of chromosome 9. The pregnancy continued and neonatal blood testing showed a mosaic trisomy 9 karyotype, i.e. 4/50 cells analysed. Clinical postnatal follow-up for a period of 1 year has documented only minor facial dysmorphism and skeletal abnormalities. Development appears unremarkable. This case is the second report of maternal uniparental disomy for chromosome 9 detected prenatally and is the first case followed up post-term. This report highlights the difficulty of making informed prognostic assessments in such cases despite extensive laboratory investigation.

Prenatal diagnosis of trisomy 20 mosaicism by maternal serum screening for Down syndrome

We report two cases of prenatally diagnosed trisomy 20 mosaicism associated with positive Down syndrome screening at 16 weeks' gestation. Both infants exhibited normal growth and mental development. These cases suggest that the multiple-marker screening test may play an important role in prenatal detection and diagnosis of chromosomal anomalies in addition to Down syndrome.

First trimester prenatal diagnosis: chorionic villus sampling

Chorionic villus sampling has been used successfully for first trimester diagnosis of genetic disorders for over 14 years. When performed between 10 and 14 weeks' gestation, it is both safe and effective in the diagnosis of fetal chromosomal, biochemical, and molecular disorders, with risks comparable to those of second trimester amniocentesis. Cytogenetic results have been confirmed to be reliable and accurate. Although confined placental mosaicism occurs in approximately 1% of cases requiring interpretation, and occasionally additional invasive testing, its finding adds additional information about perinatal outcome and can alert the practitioner to fetal genetic disorders. Earlier concerns about procedure-induced limb defects have been reduced with the accumulation of additional data, showing minimal to no risk when chorionic villus sampling is performed after 70 days of gestation. In experienced hands, it may be the procedure of choice for sampling multiple gestations. Secondary to the advantage of safe, early diagnosis, chorionic villus sampling appears to be the optimal choice for first trimester testing.

Mosaic trisomy 16 ascertained through amniocentesis: evaluation of 11 new cases

Trisomy 16, once thought to result uniformly in early pregnancy loss, has been detected in chorionic villus samples (CVS) from on-going pregnancies and was initially ascribed to a second, nonviable pregnancy. Prenatally detected trisomy 16 in CVS and its resolution to disomy has led to the reexamination of the viability of trisomy 16. This study evaluates 11 cases of mosaic trisomy 16 detected through second trimester amniocentesis. In 9 of the 11 cases, amniocenteses were performed in women under the age of 35 because of abnormal levels of maternal serum alpha-fetoprotein (MSAFP) or maternal serum human chorionic gonadotropin (MShCG). The other two amniocenteses were performed for advanced maternal age. Five of the 11 pregnancies resulted in liveborn infants, and six pregnancies were electively terminated. The liveborn infants all had some combination of intrauterine growth retardation (IUGR), congenital heart defects (CHD), or minor anomalies. Two of them died neonatally because of complications of severe congenital heart defects. The three surviving children have variable growth retardation, developmental delay, congenital anomalies, and/or minor anomalies. In the terminated pregnancies, the four fetuses evaluated by ultrasound or autopsy demonstrated various congenital anomalies and/or IUGR. Cytogenetic and fluorescent in situ hybridization studies identified true mosaicism in 5 of 10 cases examined, although the abnormal cell line was never seen in more than 1% of cultured lymphocytes. Placental mosaicism was seen in all placentas examined and was associated with IUGR in four of seven cases. Maternal uniparental disomy was identified in three cases. Mosaic trisomy 16 detected through amniocentesis is not a benign finding but associated with a high risk of abnormal outcome, most commonly IUGR, CHD, developmental delay, and minor anomalies. The various outcomes may reflect the diversity of mechanisms involved in the resolution of this abnormality. As 80% of these patients were ascertained because of the presence of abnormal levels of MSAFP or MShCG, the increased use of maternal serum screening should bring more such cases to clinical attention.

True trisomy 2 mosaicism in amniocytes and newborn liver associated with multiple system abnormalities

Among 58,000 amniocenteses completed, our laboratories found one case of true cytogenetic trisomy 2 mosaicism in a fetus with multiple abnormalities. In contrast, 11 fetuses phenotypically normal at birth were found to have true trisomy 2 mosaicism in their chorionic villus cells among the 10,500 fetuses tested by chorionic villus sampling (CVS). In our single abnormal case, amniocentesis performed at 19 weeks after finding an elevated maternal serum AFP found two independent cultures with trisomy 2 karyotypes in 8 of 25 and 7 of 31 amniocytes, respectively. Although oligohydramnios was noted by ultrasound, the mother elected to continue the pregnancy. At 26 weeks the fetus had intrauterine growth retardation (IUGR), hydronephrosis, and cardiac abnormalities. When delivered by Cesarean section at 30 weeks, the infant had multiple anomalies and developed necrotizing enterocolitis and severe cholestasis. At 5 months coronal magnetic resonance imaging (MRI) displayed delayed myelination and abnormal brain morphology. The patient also exhibited significant growth failure and developmental delay. Although chromosomes were normal in blood, skin fibroblasts, and ascites fluid cells, 4 of 100 hepatic biopsy fibroblasts were 47,XY,+2. Molecular analysis excluded uniparental disomy (UPD) of chromosome 2 in the 46,XY cell line. This and other reports of rare phenotypically abnormal trisomy 2 mosaic fetuses identified by karyotyping amniocytes emphasizes the substantially higher fetal risk of abnormal development than when trisomy 2 is found only in chorionic villus cells.

A case of mosaic trisomy 2 diagnosed at amniocentesis in an abnormal fetus and confirmed in multiple fetal tissues

Pseudomosaicism for trisomy 2 is a relatively common finding at amniocentesis. However, genuine trisomy 2 mosaicism is extremely rare. As a result, very few cases have been described and little information is available with which to counsel the parents of an affected fetus. We describe a case of mosaic trisomy 2 diagnosed at amniocentesis in a fetus with multiple anomalies on ultrasound scan. Following termination of pregnancy, the fetus was found to have mild dysmorphic features, together with an absent gall bladder, cystic left kidney, a 13th left rib and mild unilateral talipes. The presence of trisomy 2 cells was confirmed by both standard cytogenetic analysis and fluorescent in-situ hybridisation techniques in multiple fetal tissues, as well as in the cord and placenta.

Misinterpretation of trisomy 18 as a pseudomosaicism at third-trimester amniocentesis of a child with a mosaic 46,XY/47,XY, +3/48,XXY, +18 karyotype

False-negative trisomy 18 has been reported after chorionic villus sampling, but not after amniocentesis. We describe a double aneuploidy in cultured amniocytes that was initially misinterpreted as a pseudomosaicism. A patient was referred at 31 weeks of gestation because of fetal anomalies at ultrasound examination. Karyotyping of amniocytes showed a 47,XY, +3 karyotype in 61 clones and a 48,XXY, +18 karyotype in one clone. The latter was interpreted as a pseudomosaicism, the more since a second amniocentesis revealed only cells with a 47,XY, +3 karyotype. At 36 weeks gestational age, a boy was born with congenital anomalies suggestive of trisomy 18. A blood culture showed a 48,XXY, +18 karyotype, while in fibroblasts a 47,XY, + 3/48,XXY, +18 mosaicism was found. Umbilical cord and bladder epithelial tissue also revealed normal 46,XY cells, besides the aneuploid cells. Therefore, the child proper had a 46,XY/47,XY, +3/48,XXY, +18 mosaicism with the clinical symptoms of trisomy 18. To the best of our knowledge, this is the first report of a false-negative result of trisomy 18 together with three sex chromosomes after amniocentesis.

Rare trisomy mosaicism diagnosed in amniocytes, involving an autosome other than chromosomes 13, 18, 20, and 21: karyotype/phenotype correlations

In order to determine the significance of trisomy mosaicism of an autosome other than chromosomes 13, 18, 20, and 21, 151 such cases diagnosed prenatally through amniocentesis were reviewed. These rare trisomy mosaicism cases include 54 from 17 cytogenetic laboratories, 34 from a previous North American mosaicism survey, and 63 from published reports. All were cases of true mosaicism with information available on pregnancy outcome, and with no evidence of biased ascertainment. There were 11 cases of 46/47, +2; 2 of 46/47, +3; 2 of 46/47, +4; 5 of 46/47, +5; 3 of 46/47, +6; 8 of 46/47, +7; 14 of 46/47, +8; 25 of 46/47, +9; 2 of 46/47, +11; 23 of 46/47, +12; 5 of 46/47, +14; 11 of 46/47, +15; 21 of 46/47, +16; 7 of 46/47, +17; 1 of 46/47, +19; and 11 of 46/47, +22. As to the risk of an abnormal outcome, the data showed a very high risk (> 60 per cent) for 46/47, +2, 46/47, +16, and 46/47, +22; a high risk (40-59 per cent) for 46/47, +5, 46/47, +9, 46/47, +14, and 46/47, +15; a moderately high risk (20-39 per cent) for 46/47, +12; a moderate risk (up to 19 per cent) for 46/47, +7 and 46/47, +7 and 46/47, +8; a low risk for 46/47, +17; and an undetermined risk, due to lack of cases, for the remaining autosomal trisomy mosaics. Most cases were evaluated at birth or at termination, so subtle abnormalities may have escaped detection and developmental retardation was not evaluated at all. Comparison of the phenotypes of prenatally diagnosed abnormal cases and postnatally diagnosed cases with the same diagnosis showed considerable concordance. Since the majority of anomalies noted are prenatally detectable with ultrasound, an ultrasound examination should be performed in all prenatally diagnosed cases. In cytogenetic confirmation studies, the data showed much higher confirmation rates in cases with abnormal outcomes than in cases with normal outcomes [81 per cent vs. 55 per cent for fibroblasts (from skin, fetal tissue, and/or cord); 88 per cent vs. 46 per cent for placental cells; 22 per cent vs. 10 per cent for blood cells]. The confirmation rate reached 85 per cent when both fibroblasts and placental tissues were studied in the same case (with trisomic cells found in one or the other, or both). Therefore, one must emphasize that both fibroblasts and placental tissues should be studied. Except for 46/47, +8 and 46/47, +9, PUBS is of limited value for prenatal diagnosis of rate trisomy mosaicism. DNA studies for UPD are suggested for certain chromosomes with established imprinting effects, such as chromosomes 7, 11, 14, and 15, and perhaps for chromosomes 2 and 16, where imprinting effects are likely.

Chorionic villus sampling

Chorionic villus sampling (CVS) has been used a successful and safe first-trimester prenatal diagnostic technique for over 12 years. Developed to avoid the medical and psychological complications of later prenatal diagnosis by amniocentesis, CVS rapidly has become a primary tool for the diagnosis of fetal cytogenetic, molecular, and biochemical disorders. In addition, its development has led to an improved understanding of several biological processes, including confined placental mosaicism and uniparental disomy.

Prenatal diagnosis of an infant with mosaic trisomy 16 of paternal origin

We present the first case of an infant with paternally-derived mosaic trisomy 16. Amniocentesis following an elevated maternal serum alpha-fetoprotein level and early fetal growth restriction at 19 weeks detected a high level of mosaicism with 25/33 colonies demonstrating trisomy 16 and 8/33 colonies with a normal 46,XX karyotype. Molecular studies revealed a paternal origin of the trisomy which was present in amniotic fluid cells, representing either a post-zygotic error or a meiosis II non-disjunction without crossing-over. In addition, there was normal biparental inheritance in the normal cell line. The symmetrically growth-restricted fetus was closely monitored for the remainder of the gestation. Decreased fetal movements at 36 weeks in conjunction with electronic fetal monitoring showing evidence of fetal distress necessitated abdominal delivery. Severe growth restriction, mild facial dysmorphism, and cardiac anomalies were identified. Microsatellite analysis demonstrated biparental inheritance in skin fibroblasts with a paternal origin for the trisomy in the placenta. Follow-up cytogenetic studies of additional tissues revealed 85 per cent trisomy 16 mosaicism in the placenta, yet only cytogenetically normal cells in lymphocytes and fibroblasts.

Incidence and significance of chromosome mosaicism involving an autosomal structural abnormality diagnosed prenatally through amniocentesis: a collaborative study

Among 179,663 prenatal diagnosis cases collected from ten institutions and two publications, 555 (0.3 per cent) were diagnosed as having chromosome mosaicism. Of these, 57 (10.3 per cent) were mosaic for an autosomal structural abnormality, 28 (5 per cent) for a sex chromosome structural abnormality, and 85 (15.3 per cent) were mosaic for a marker chromosome. Ninety-five cases of prenatally diagnosed mosaicism with a structural abnormality in an autosome and a normal cell line, and with a known phenotypic outcome, were collected for karyotype-phenotype correlations through our collaboration (40 cases), a prior survey (26 cases), and published reports (29 cases). They included 13 balanced reciprocal translocations, one unbalanced reciprocal translocation, four balanced Robertsonian translocations, four unbalanced Robertsonian translocations, four inversions, 17 deletions, three ring chromosomes, 19 i(20q), seven +i(12p), six other isochromosomes, and 17 partial trisomies resulting from a duplication or other rearrangement. All cases mosaic for a balanced structural rearrangement resulted in a normal phenotype. All cases of 46/46,i(20q) resulted in normal liveborns. Five of seven cases with 46/47,+i(12p) had an abnormal phenotype compatible with Killian-Pallister syndrome. The overall risk for an abnormal outcome for a mosaic case with an unbalanced structural abnormality, excluding 46/46,i(20q) and 46/47,+i(12p), is 40.4 per cent. In the same category, the study also suggested a correlation between the percentage of abnormal cells and an abnormal phenotype. For mosaicism involving a terminal deletion, the possibility of a familial fragile site should be considered.

Maternal cell contamination in uncultured amniotic fluid

The presence of maternal cells in uncultured amniotic fluid may result in error in the interpretation of prenatal tests such as direct DNA analysis and rapid aneuploidy detection by fluorescence in situ hybridization (FISH). Using simultaneous dual colour X and Y FISH, we assessed maternal cell contamination in uncultured amniotic fluids from 500 women carrying male fetuses. The presence of maternal cells was correlated with the amount of blood present in the amniotic fluid as defined by visual examination of the cell pellet after centrifugation. The overall rate of maternal cell contamination in uncultured amniotic fluid as identified using X and Y-specific probes was 21.4 per cent, compared with 0.2 per cent in cultured fluid. Sixteen per cent of slightly bloody and 55 per cent of moderately bloody uncultured fluids had at least 20 per cent maternal cells and were classified as uninformative according to our protocol for rapid aneuploidy detection. Maternal and fetal cells could not be distinguished based on morphological characteristics alone.

Is the 15-in situ clone protocol necessary to detect amniotic fluid mosaicism?

OBJECTIVE

Our purpose was to evaluate the 15-clone analysis for detecting amniotic fluid mosaicism by the in situ method.

STUDY DESIGN

A 10-year review was performed of all amniotic fluid mosaicism cases at two institutions using the in situ method exclusively, with sequential clonal analysis to determine the first and second clone in which the abnormal cell line occurred.

RESULTS

Of the 28,497 amniotic fluid samples, 73 met criteria for amniotic fluid mosaicism by in situ method (0.26%). There were 54 cases (0.19%) with potential clinical significance (23 autosome and 31 sex chromosome mosaicism); 49 of the 54 cases (89%) were detected in the first six clones, including 22 of 23 involving autosomes and 27 of 31 involving sex chromosomes. In one of the six cases detected after clone 6 (46,XX/47,XX,+21) the mosaic cell line was present in 20% of the clones analyzed and was followed by a voluntary termination of the pregnancy. In the other five cases amniotic fluid mosaicism was present in < 20% of the clones; these included one case of 46,XX/47,XX+mar (15% amniotic fluid mosaicism, voluntary termination of pregnancy), two cases of 45,X/46,XY (10% to 12% amniotic fluid mosaicism, both normal at birth), and two cases of 45,X/46,XX (8% amniotic fluid mosaicism, lost to follow-up; 12% amniotic fluid mosaicism, voluntary termination of pregnancy). By limiting the analysis to six clones, approximately 20% of analysis time could be saved per case, but one autosomal amniotic fluid mosaicism case per 10,000 samples could potentially be missed.

CONCLUSION

Reducing the number of clones analyzed by in situ method could result in increased efficiency, decreased costs, and minimal loss of sensitivity.

Balanced reciprocal translocation mosaicism: how frequent?

We describe 2 cases of balanced reciprocal translocation (BRT) mosaicism. The frequency of this aberration in the population referred to our laboratory was determined and compared to those frequencies reported in the literature by other clinical cytogenetics laboratories. The extent of BRT mosaicism was also examined in surveys of parental populations, which are less likely to have a bias due to ascertainment on the basis of abnormal phenotype. the frequencies in the postnatal and prenatal populations examined in this study were calculated to be 5.7 x 10(-5) (95% confidence interval is 3.2-8.2 x 10(-5)) and 4.1 x 10(-5) (95% confidence interval is 2.0-6.2 x 10(-5)). However, in view of the extent of variation reported in the various studies, these estimates should be considered first approximations of the true frequency.

Prenatal diagnosis of mosaic 4p- in a fetus with trisomy 21

Mosaicism for the Wolf-Hirschhorn syndrome, del(4)(p16), is extremely rare and has not been reported in association with a numerical chromosome abnormality. We report the prenatal diagnosis of mosaic del(4)(p16) and non-mosaic trisomy 21 in a 16-week female fetus. The pregnancy ended in spontaneous abortion at 34 weeks secondary to fetal demise. The fetus had features of both 4p- and trisomy 21.

46,XY,dup(10q) in direct CVS preparation and mosaic 48,XXXY,dup(10q) in CVS long-term culture and fetal tissue

Chorionic villus sampling (CVS) was performed on a 40-year-old woman at 9 1/2 menstrual weeks because of advanced maternal age. The direct preparation showed 46,XY,dup(10)(q11.2q23.2). CVS long-term culture and fetal tissue revealed a rare additional abnormality: 48,XXXY,dup(10)(q11.2q23.2). This abnormality represented the major cell line (> 85 per cent in 691 cells) in an (XY)/XXY/XXXY/(XXXXY) mosaic (all cell lines presumably bearing the dup(10q); the presence of XY and XXXXY cell lines is uncertain). To our knowledge, this is the first report of trisomy 10q11-q23 and of prenatally detected 48,XXXY in chorionic villi. The mosaic could have resulted from early post-zygotic non-disjunctions in a 46,XY,dup(10q) or 47,XXY,dup(10q) zygote. The results from DNA studies of four polymorphisms, mapped to Xp and Xq, support this theory. The literature on prenatally detected cases with sex chromosome tetrasomy and pentasomy and those with additional autosomal abnormalities is reviewed. The reported case underlines the problem of false-negative findings when only direct CVS preparations are karyotyped.

Prenatal diagnosis of 46,XX/47,XXY mosaicism: a case report

A case of 46,XX/47,XXY mosaicism was diagnosed at 22 gestational weeks by amniocentesis and fetal blood sampling. After genetic counselling, the couple elected to have the pregnancy terminated. Culture of the fetal skin and both gonads confirmed the prenatal diagnosis. In external appearance, the abortus had no remarkable findings except hypospadia. Histology of both gonads showed testicular tissue without evidence of ovarian components.

Detection of maternal cell contamination in amniotic fluid cell cultures using fluorescent labelled microsatellites

A rapid PCR based assay was used to ascertain the presence of maternal cell contamination (MCC) in amniotic fluid cell cultures and to exclude MCC in cases where cytogenetic analysis was possible only from one primary cell culture. Six 6-carboxyfluorescein (FAM) and three 6-carboxyfluorescein hexachloride (HEX) labelled primer sets were used to amplify two tetra- and seven dinucleotide repeat polymorphisms. The PCR amplifications were multiplexed in (three) three primer set reactions and visualised on an Applied Biosystems 373A sequencer running Genescan 672 software. The microsatellite products obtained from 200 amniotic fluid cell cultures where the karyotype was female were compared against corresponding maternal blood PCR products. A single case of MCC was detected indicating the usefulness of such assays. We suggest that screening for MCC should be considered in instances where the amniotic fluid sample is bloodstained or was obtained with difficulty, or where the karyotype is female and chromosome analysis is not possible from more than one primary cell culture.

Chorionic villi sampling: laboratory experience with 4,000 consecutive cases

Experience with 4,000 consecutive CVS cases shows that 1) the combination of both the direct and culture methods greatly reduces false diagnoses and maternal cell contamination; 2) the time interval between the sampling procedure and processing of villus specimens influences the quality of direct preparations; 3) maternal cell contamination (MCC) can be minimized with dissection of CVS specimens. We have compiled a large volume of confined placental mosaicism (CPM) cases to serve as a resource in interpreting mosaic cytogenetic findings. It was noted that, in up to 92% of the mosaic cases, the abnormal cell line was confined to the placenta. The frequency of true chromosomal mosaicism was 0.2%, and is not different from that for amniocentesis.

Phenotype/karyotype correlations of Y chromosome aneuploidy with emphasis on structural aberrations in postnatally diagnosed cases

Over 600 cases with a Y aneuploidy (other than non-mosaic 47,XYY) were reviewed for phenotype/karyotype correlations. Except for 93 prenatally diagnosed cases of mosaicism 45,X/46,XY (79 cases), 45,X/47,XYY (8 cases), and 45,X/46,XY/47,XYY (6 cases), all other cases were ascertained postnatally. Special emphasis was placed on structural abnormalities. This review includes 11 cases of 46,XYp-; 90 cases of 46,XYq- (52 cases non-mosaic; 38 cases 45,X mosaic); 34 cases of 46,X,r(Y) (9 cases non-mosaic and 25 cases 45,X mosaic); 8 cases of 46,X,i(Yp) (4 non-mosaic and 4 mosaic with 45,X); 12 cases of 46,X,i(Yq) (7 non-mosaic and 5 mosaic); 44 cases of 46,X,idic(Yq); 80 cases of 46,X, idic(Yp) (74 cases had breakpoints at Yq11 and 6 cases had breakpoints at Yq12); 130 cases of Y/autosome translocations (50 cases with a Y/A reciprocal translocation, 20 cases of Y/A translocation in 45,X males, 60 cases of Y/DP or Y/Gp translocations); 52 cases of Y/X translocations [47 cases with der(X); 4 cases with der(Y), and 1 case with 45,X with a der(X)], 7 cases of Y/Y translocations; 151 postnatally diagnosed cases of 45,X/46,XY; 14 postnatally diagnosed cases of 45,X/47,XYY; 18 cases of 45,X/46,XY/47,XYY; and 93 aforementioned prenatally diagnosed cases with a 45,X cell line. It is clear that in the absence of a 45,X cell line, the presence of an entire Yp or a region of it including SRY would lead to a male phenotype in an individual with a Y aneuploidy, whereas the lack of Yp invariably leads to a female phenotype with typical or atypical Ullrich-Turner syndrome (UTS). Once there is a 45,X cell line, regardless of whether there is Yp, Yq, or both Yp and Yq, or even a free Y chromosome in other cell line, there is an increased chance for that individual to be a phenotypic female with UTS manifestations or to have ambiguous external genitalia. This review once again shows a major difference in reported phenotypes between postnatally and prenatally diagnosed cases of 45,X/46,XY, 45,X/47,XYY, and 45,X/46,XY/47,XYY mosaicism. It appears that ascertainment bias can explain the fact that all known patients with postnatal diagnosis are phenotypically abnormal, while over 90% of prenatally diagnosed cases are reported to have a normal male phenotype. Further elucidation of major Y genes and their clinical significance can be expected in the rapidly expanding gene mapping projects. More, consequently better, phenotype/karyotype correlations can be anticipated at both the cytogenetic and the molecular level.

Postnatal confirmation of prenatally diagnosed trisomy 16 mosaicism in two phenotypically abnormal liveborns

Two phenotypically abnormal liveborns in whom trisomy 16 mosaicism was diagnosed prenatally by amniocentesis are described. Analysis of a percutaneous umbilical blood sample in one case revealed a normal chromosomal complement. Ultrasound examinations performed at the time of amniocentesis were normal. Serial sonography during the late second and third trimesters demonstrated progressive intrauterine growth retardation (IUGR) in both fetuses and a cardiac defect in one. At birth, both infants had dysmorphic features and multiple congenital anomalies. Trisomy 16 mosaicism was confirmed postnatally in both infants in skin fibroblasts; however, peripheral blood samples contained only chromosomally normal cells. The two mosaic trisomy 16 cases described in this report, together with the five confirmed cases reported previously, demonstrate the need for caution in the counselling of patients when trisomy 16 mosaicism is diagnosed prenatally in amniotic fluid samples. Such cases potentially can result in the birth of dysmorphic infants with significant birth defects, growth retardation, and possible developmental disabilities.

Prenatal diagnosis of trisomy 12 mosaicism: physical and developmental follow-up

Follow-up evaluations were performed on a child at the ages of 2 years 8 months and also at 5 years who had been found on prenatal amniocentesis to be mosaic for trisomy 12. Eight of 36 colonies (22 per cent) were trisomy 12 at amniocentesis, with the remaining colonies showing a normal female karyotype. Cord blood, amnion, chorion, placental, and skin fibroblast chromosome studies failed to show any further evidence of a trisomy 12 cell line. At her evaluations, the child had normal physical and neurological findings. Psychomotor development was appropriate for age on screening.

Asymmetry and skin pigmentary anomalies in chromosome mosaicism

We report six persons mosaic for a chromosome anomaly. All were mentally retarded and dysmorphic. Unilateral or asymmetrical features were found in all cases, in one an unusual transverse terminal limb anomaly, and in the others various degrees of hemiatrophy of the left side of the body. Five of the subjects had skin pigmentary anomalies which were distributed in the lines of Blaschko. The abnormal cell lines found were ring chromosome 22, trisomy 22, a large acrocentric marker, a deletion of 18q, a deletion of 8q, and triploidy. In four cases the clinical diagnosis was only confirmed by skin biopsy. In one case low level mosaicism in blood was fortuitously detected because of cytogenetic fragile X screening and confirmed in a skin biopsy. The sixth case was of dynamic mosaicism of a non-mosaic deletion 18q with a chromosome 18 derived marker present in a proportion of cells. Chromosome mosaicisn may cause subtle and asymmetrical clinical features and can require repeated cytogenetic investigations. The diagnosis should be actively sought as it enables accurate genetic counselling to be given.

Complex genetic counseling and exclusion of Duchenne muscular dystrophy in a twin pregnancy after in vitro fertilization (IVF)

A twin pregnancy following in vitro fertilization-embryo transfer coincidentally at risk for the X-linked recessive Duchenne muscular dystrophy is described. First-trimester prenatal diagnosis by transabdominal chorionic villus samplings on the dichorionic placentae and molecular linkage analysis could exclude the disorder in both fetuses. Genetic counseling and prenatal diagnosis were particularly complex due to the twin pregnancy, the need for linkage analysis, and confined placental mosaicism 45,X/46XX in one of the fetuses. All parties should be aware that additional invasive diagnostic procedures in the second trimester might be required. It is proposed that, in similar situations, only one, arguably two, fertilized egg be transferred at a time to facilitate prenatal diagnosis and decision making for these rare couples. This problem, however, may be increasingly overcome by preimplantation diagnosis.

Prenatal confirmation of trisomy 12 mosaicism by fetal skin biopsy

Trisomy 12 mosaicism diagnosed at 16 weeks' amniocentesis in a 42-year-old woman was not confirmed at 18 weeks' gestational age in amniotic fluid or fetal blood. Fetal skin biopsy performed at the same time did, however, allow the detection of trisomy 12 in 1 of 14 fibroblasts analysed. Fetal skin biopsy can be included within the diagnostic procedures to be performed when a level III mosaicism is found in the amniotic fluid.

Fluorescent in situ hybridization (FISH): a new application in the delineation of true vs. pseudomosaicism in prenatal diagnosis

Metaphase chromosomes and interphase nuclei from nine amniotic fluid cultures were studied with fluorescence in situ hybridization (FISH). The samples were initially analyzed with routine G-banding and were diagnosed as having true mosaicism (five patients) or pseudomosaicism (four patients). In our study, FISH analysis could provide additional information to distinguish pseudo- from true mosaicism by allowing interphase studies and analysis of an increased number of metaphase spreads. These results suggest a multilinear origin of 'in situ' colonies of cells.