Three different origins for apparent triploid/diploid mosaics

Four apparent triploid/diploid mosaic cases were studied. Three of the cases were detected at prenatal diagnosis and the other was of an intellectually handicapped, dysmorphic boy. Karyotypes were performed in multiple tissues if possible, and the inheritance of microsatellites was studied with DNA from fetal tissues and parental blood. Non-mosaic triploids have a different origin from these mosaics with simple digyny or diandry documented in many cases. Three different mechanisms of origin for these apparent mosaics were detected: (1) chimaerism with karyotypes from two separate zygotes developing into a single individual, (2) delayed digyny, by incorporation of a pronucleus from a second polar body into one embryonic blastomere, and (3) delayed dispermy, similarly, by incorporation of a second sperm pronucleus into one embryonic blastomere. In three of the four cases, there was segregation within the embryos of triploid and diploid cell lines into different tissues from which DNA could be isolated. In case 2 originating by digyny, the same sperm allele at each locus could be detected in both triploid and diploid tissues, which is supportive evidence for the involvement of a single sperm and for true mosaicism rather than chimaerism. Similarly, in case 4 originating by dispermy, the same single ovum allele at each locus could be detected in diploid and triploid tissues, confirming mosaicism. In the chimaeric case (case 3), the diploid line had the karyotype 47,XY,+16 while the triploid line was 69,XXY. This suggests a chimaera, since, in a true mosaic, the triploid line should also contain the additional chromosome 16. Supporting the interpretation of a chimaeric origin for this case, the DNA data showed that the triploidy was consistent with MII non-disjunction (i.e. involving a diploid ovum). In the mosaic cases (1, 2, 4), there was no evidence of the involvement of a diploid sperm or a diploid ova, and in triploid/diploid mosaicism, an origin from a diploid gamete is excluded, since all such conceptuses would be simple triploids. In one of these triploid/diploid mosaics detected at prenatal diagnosis by CVS, the triploid line seemed to be sequestered into the extra-fetal tissues (confined placental mosaicism). This fetus developed normally and a normal infant was born with no evidence of triploidy in newborn blood or cord blood at three months of age. Copyright © 2003 John Wiley & Sons, Ltd.     

Second trimester maternal serum analytes in triploid pregnancies: correlation with phenotype and sex chromosome complement

Second trimester maternal serum alpha-fetoprotein (MS-AFP), human chorionic gonadotrophin (hCG), unconjugated estiol (uE3), and inhibin-A (INH-A) levels were evaluated in pregnancies complicated by triploidy. In addition to seven new triploid pregnancies, the results for 67 published cases were reviewed. All cases appear to fall into two major groups. First, those identifiable as screen-positive for both Down syndrome and an open neural tube defect (ONTD) with elevated MS-AFP, grossly elevated hCG, low/normal uE3, and probably elevated INH-A. Pregnancies in the second group are identifiable as screen-positive for trisomy 18 with low/normal MS-AFP, and very low hCG, uE3 and INH-A. Triploid pregnancies with high maternal serum hCG nearly always show a placenta with partial mole (25/27 or 93%), a high frequency of ONTDs or ventral wall defects (VWDs) (8/28 or 29%) and have either an XXX or XXY karyotype (observed ratio 6:10, respectively). Low hCG is infrequently associated with a molar placenta (1/11 or 9%), does not appear to be associated with ONTDs or VWDs (0/29 or 0%), and shows an excess of XXX over XXY karyotypes (observed ratio 17:2). There were 16 cases with either a molar placenta, an ONTD or a VWD that received the MS-AFP and hCG tests. All 16 were screen-positive for an ONTD (MS-AFP≥2 multiples of the median). In addition, all 31 cases that received MS-AFP, hCG, uE3 (and where available INH-A) were screen-positive for either Down syndrome or trisomy 18. The findings are discussed in the context of expected differences between digynic and diandric triploidy. It is suggested that the sex chromosome complement in triploidy is an important factor in determining risk for partial mole development and in utero survival. Copyright © 2001 John Wiley & Sons, Ltd.     

Prenatal diagnosis of mosaicism for triploidy and trisomy 13

Mosaicism for trisomy 13 and triploidy was detected by amniocentesis performed at 18 weeks' gestation because of fetal anomalies. Pregnancy continued and a live-born male was delivered vaginally at 37 weeks. The infant had features common to both trisomy 13 and triploidy: intrauterine growth retardation (IUGR), small abnormal ears, cleft palate, and a small jaw. In addition, he had complete cutaneous syndactyly of fingers 3 and 4 and partial syndactyly of the toes, as seen in triploidy. Mixoploidy for trisomy 13 and triploidy was confirmed postnatally in blood, skin, and placenta. Examination of chromosome heteromorphisms and DNA markers suggested the presence of two maternal contributions in the triploid cell line. In addition, the extra chromosome 13 in the trisomic cell line was derived from the mother. Copyright © 2001 John Wiley & Sons, Ltd.     

Trisomy 16 confined to the placenta

Two cases with trisomy 16 confined to the placenta are presented. Prenatal diagnosis was indicated because of fetal growth retardation. In case 1, a phenotypically normal but small-for-date boy was born. In case 2, the fetus turned out to be triploid on cordocentesis. In both instances the trisomy 16 was recovered from the placenta. Recovery indicates that the abnormality was present in the placenta during the time of fetal growth retardation, which supports an aetiological relationship. Strict appliance of the current models cannot readily explain the observed discrepancies. In case 2, a chimeric placenta as a result of a vanishing twin is assumed. Cases of placental trisomy 16 published after 1988 are reviewed. It is concluded that confined placental trisomy 16 can cause intrauterine growth retardation if present in both the direct preparation and the villus culture. The chances of finding a chromosomally abnormal fetus (mosaic trisomy 16, triploidy) after diagnosis of trisomy 16 in chorionic villi are low but warrant further investigations.     

Rapid prenatal diagnosis of 14 cases of triploidy using fish with multiple probes

Fluorescence in situ hybridization (FISH) of chromosome-specific probes to interphase nuclei can rapidly identify aneuploidies in uncultured amniotic fluid cells. Using DNA probe sets specific for chromosomes 13, 18, 21, X, and Y, we have identified 14 fetuses where the hybridization pattern was consistent with a triploid chromosome constitution. In each case, the identification of fetal abnormalities by ultrasound examination initiated a request for rapid determination of ploidy status via prenatal FISH analysis of uncultured amniocytes. FISH produced a three-signal pattern for the three autosomes in combination with signals indicating an XXX or XXY sex chromosome complement. This hybridization pattern was interpreted to be consistent with triploidy. Results were reported to the physician within 2 days of amniocentesis and subsequently confirmed by cytogenetics. These cases demonstrate the utility of FISH for rapid prenatal identification of triploidy, particularly when fetal abnormalities are seen with ultrasonographic examination.     

Prenatal ascertainment of triploidy by maternal serum alpha-fetoprotein screening

We report our experience in ascertaining fetal triploidy during routine maternal serum alpha-fetoprotein (MSAFP) screening. Three cases were identified after elevated MSAFP tests. Two of the three had normal amniotic fluid alpha-fetoprotein (AFAFP). The third had amniocentesis too late for AFAFP interpretation. Three additional cases were detected by amniocentesis without prior MSAFP screening and none had an elevated AFAFP. A literature review revealed eight triploid fetuses detected as a result of an elevated MSAFP. Of the five with AFAFP quantitation, only one had an abnormal value and the elevation was minimal. In these 14 cases from our own and other reports, ultrasound findings of placental and fetal abnormalities were often noted, but a pattern diagnostic of triploidy was not present. We conclude that, for optimal prenatal detection of triploidy, fetal karyotyping should be included when an amniocentesis is performed for elevated MSAFP.     

Triploidy: Pregnancy complications and clinical findings in seven cases

Seven cases of triploidy were encountered by the Prenatal Diagnosis Program at Dartmouth–Hitchcock Medical Center over an 8-year period through associated pregnancy complications. We describe the characteristic findings that facilitate prenatal diagnosis and management. Our experience includes fetuses with major central nervous system abnormalities (spina bifida aperta, holoprosencephaly) and anterior abdominal wall defects, which are detectable with routine prenatal diagnostic screening examinations (ultrasound and AFP). In addition, we stress the importance of recognizing obstetric complications and associated cystic placental changes, which are quite common among triploid conceptuses. Molar changes associated with triploidy have a more benign prognosis than that associated with diploid moles. Such molar changes may relate to the presence of a diploid paternal chromosome complement. The usefulness of cytofluorometric DNA determinations in helping to confirm a clinical suspicion of triploidy is emphasized. These cases are presented in an effort to facilitate prenatal recognition and management of this common cytogenetic condition and prevent unnecessary Caesarean section deliveries.     

Detection of fetal cells in transcervical samples and prenatal diagnosis of chromosomal abnormalities

Transcervical samples collected by lavage, aspiration, and cytobrush from women between 6 and 13 weeks of gestation were tested for the presence of fetal cells using fluorescence in situ hybridization (FISH) with probes for chromosomes X, Y, 1, and 21, and by polymerase chain reaction (PCR) amplification of DNA sequences derived from chromosomes X, Y, and 21. With a few exceptions, a good correlation was observed between the results of sexing the fetuses using FISH or PCR on transcervical cell (TCC) samples retrieved by lavage and those obtained by testing fetal (placental) tissue. In a comparative study between TCC samples collected by lavage or cytobrush, the sex of the fetus was correctly diagnosed by PCR amplification of a Y-derived DNA sequence. Variable results were observed with samples obtained by aspiration, mainly because this procedure was found to be more prone to failure to remove thick mucus without previous injection of physiological saline. Chromosome 21-derived small tandem repeats (STRs) of fetal origin were successfully detected in about 40 per cent of TCC samples recovered by lavage. Two cases of chromosomal abnormalities, one of trisomy 21 and one of triploidy, were detected in TCC samples in the course of our investigations.     

Ultrasound movement patterns of fetuses with chromosome anomalies

Fetal movements were examined by ultrasound in 24 pregnancies in which an abnormal karyotype was detected in fetal cells and compared to ultrasound fetal movement patterns in normal pregnancies. The main features in fetuses with chromosome anomalies observed at 18–20 weeks of gestation are the persistence of global, jerky movements with twitches usually seen at 13–14 weeks of gestation in normal fetuses. This fetal motor behaviour is inconstant in trisomy 21. In trisomy 18 the hand deformities are easily detected.     

Fetal karyotype following ascertainment of fetal anomalies by ultrasound

Data pooled from contributors to a Registry for Cytogenetic Abnormalities and PKU (ReCAP) shows an unbalanced chromosome abnormality rate of 27 per cent (29 fetuses) for 107 fetuses with ultrasonically diagnosed fetal anomalies. Of the abnormal, 12 were trisomic, 6 were monosomy X and 6 were structural abnormalities, 4 were mosaics and one triploid.     

Mosaicism for trisomy 12: Four cases with varying outcomes

Trisomy 12 observed in chorionic villus sampling (CVS) may reflect generalized mosaicism or indicate mosaicism confined to only the placenta. In this report, four cases of trisomy 12 observed in CVS or cultured placental biopsies with varying outcomes are presented. Seven dinucleotide repeat polymorphisms for chromosome 12 were used to determine the chromosome 12 origins in the fetus or child and to delineate the mechanism(s) that gave rise to the trisomy. In two cases (cases A and C), the mosaicism was confined to the placenta, resulting in normal liveborns. Although, in one case, the molecular results suggested an apparent duplication of one paternal chromosome 12 in the placenta, normal biparental inheritance was found in the diploid fetal cell line in both cases. In two other cases (cases B and D), trisomy 12 was observed in both extraembryonic and fetal tissues. In one of these pregnancies, a child was born by Caesarean section at 37 weeks because of intrauterine growth retardation and oligohydramnios, and resulted in neonatal death. Molecular markers and fluorescence in situ hybridization (FISH) revealed low-level trisomy 12 mosaicism in the spleen. In the fourth case, fetal abnormalities were detected on ultrasound and low-level trisomy 12 mosaicism was observed in amniotic fluid cells using conventional cytogenetics and FISH. Molecular markers revealed a maternal meiosis I non-disjunction of chromosome 12 in DNA from a cultured placental biopsy. Although predicting the outcomes of pregnancies involving confined placental mosaicism remains difficult, molecular techniques are valuable tools for distinguishing uniparental from biparental disomy and mechanisms of mosaicism.     

Amniotic fluid-AFP in Down syndrome and other chromosome abnormalities

80·2 Per cent of 111 Down syndrome pregnancies had amniotic fluid (AF) alpha fetoprotein (AFP) levels on or below the median and 10·8 per cent at or below 0·5 MoM compared with 41·9 and 1·4 per cent of controls. These differences were even more striking when the gestational age was < 18 weeks compared with ⩾ 18 weeks. No such association was seen for other chromosome abnormalities including trisomy 18,45,X and mosaics, 47,XXY, 47,XXX, and other structural abnormalities and triploidy, even when high levels due to defects such as omphalocele and cystic hygroma were excluded. All cases of trisomy 13 and 80 per cent with 47,XYY had AF-AFP levels above the median. Selection of cases for karyotyping by a low level of AF-AFP would clearly fail to detect aneuploidies other than Down syndrome and is not recommended. A possible weak association between low maternal serum (MS) and AF-AFPs in Down syndrome was most evident at < 18 weeks, suggesting that MS screening between 16 and 18 weeks may be the most informative time.     

Human maternal uniparental disomy for chromosome 16 and fetal development

Two severely growth-retarded fetuses found to have maternal uniparental disomy (UPD) for chromosome 16 and trisomy 16 placental mosaicism both had an unfavourable outcome. Antenatally, the first case was complicated by an unexplained raised maternal serum alpha-fetoprotein concentration, preterm premature rupture of the membranes, and growth retardation detectable at 21 weeks' gestation, whilst the other had an unexplained raised maternal serum human chorionic gonadotrophin level, a two-vessel cord on ultrasound, and cessation of growth at 25 weeks. At post-mortem, both babies had an imperforate anus. Fetal maternal UPD may explain the poor outcome that occurs in some cases of confined placental mosaicism for chromosome 16 and is also associated with specific fetal abnormalities.     

Triploid fetus: An important consideration in the evaluation of very high maternal serum alpha-fetoprotein

Two patients referred for evaluation of very high maternal serum alpha-fetoprotein (10–20 multiples of the median) were carrying triploid fetuses with placentas showing features of partial hydatidiform mole. The diagnosis of fetal triploidy should be considered when there is a very high maternal serum alpha-fetoprotein and no ultrasound evidence of open neural tube defect, ventral wall defect, or any other explanation. Therefore, chromosomal analysis of amniotic fluid cells in such cases is essential.     

Cardiac and extra-cardiac anomalies as indicators for trisomies 13 and 18: A prenatal ultrasound study

The purpose of the present study was to establish sonographic markers for prenatal diagnosis of trisomies 13 and 18. Retrospective analysis of sonographic morphology was therefore carried out in seven fetuses with trisomy 13, and 16 fetuses with trisomy 18. Gestational age ranged between 17 and 39 weeks (median 28 weeks). Polyhydramnios and symmetrical growth retardation were present in 14 of 23 fetuses. A cardiac anomaly was diagnosed in all 23 fetuses, the majority representing a ventricular septal defect (n = 8) or double outlet right ventricle (n = 8). Extra-cardiac anomalies were characterized by a high incidence of limb deformities (polydactyly, clenched hands, club feet; n = 15) and omphalocele (n = 7). We conclude that the combined appearance of cardiac and extra-cardiac anomalies should prompt fetal karyotyping. Cardiac anomalies in combination with fetal limb deformities and omphalocele are suspicious for trisomies 13 and 18.     

Abnormal immunological development in fetuses with trisomy 18

Flow cytometry was used to enumerate the lymphocyte subpopulations in fetal blood obtained by cordocentesis from eight trisomy 18 fetuses at 20–36 weeks' gestation. Compared with values in chromosomally normal fetuses, in trisomy 18 the mean T- and natural killer (NK) cell counts were significantly lower (t= − 7·63, P<0·001 and t= − 3·58, P<0·01, respectively); the mean B-cell count was not significantly different (t= − 1·32). These findings demonstrate that in trisomy 18 there is abnormal intrauterine development of the immune system.     

Quantitative evaluation of collagen type VI and SOD gene expression in the nuchal skin of human fetuses with trisomy 21

Objective To investigate the involvement of the genes encoding for COL6A1, COLA2 and super-oxide dismutase (SOD) in the mechanism for the retention of subcutaneous fluid in fetuses with trisomy 21. Methods During a 7-month period (November 2004–May 2005), human fetal skin from the nuchal region was obtained from euploid fetuses and from fetuses with trisomy 21 following abortions and terminations of pregnancy. Cell cultures were performed from nuchal skin. Quantification of COL6A1, COL6A2, COL6A3 and SOD mRNAs were performed using real-time quantitative RT-PCR. Results Twelve fetuses were studied between 13–15 and 19–20 weeks of gestation including 7 cases of trisomy 21. A significant overexpression of genes of interest was demonstrated in trisomy 21 fetuses when compared with euploid fetuses, in the first and in the second trimester of pregnancy (p < 0.0001). Conclusion This study demonstrates a homogeneous overexpression of the genes encoding for α1 and α2 chains of Collagen type VI, and SOD in nuchal skin of human trisomy 21 fetuses. Persistence of this overexpression in the second trimester of pregnancy, despite the absence of an enlarged nuchal translucency (NT), may characterize some compensatory mechanisms. Copyright © 2007 John Wiley & Sons, Ltd.     

Sonographically determined anomalies and outcome in 170 chromosomally abnormal fetuses

Structural pathology and outcome were studied in 170 chromosomally abnormal fetuses. Numerical chromosomal abnormalities were established in 158 (93 per cent) cases, of which 110 (71 per cent) represented trisomies, 30 (18 per cent) Turner syndrome, and 18 (11 per cent) triploidy. Structural chromosomal abnormalities were diagnosed in 12 (7 per cent) cases. Gestational age at referral was significantly shorter for pregnancies with Turner syndrome than for the other chromosomal abnormalities. Referral before 20 weeks of gestation was mainly based on fetal structural pathology alone (92 per cent); after 20 weeks, patients were referred because of structural pathology combined with small for gestational age, oligohydramnios, or polyhydramnios. Referral as a result of suspected multiple organ pathology occurred in 73.5 per cent of pregnancies. An abnormal amniotic fluid volume was present in 59/170 (34.5 per cent) chromosomally affected pregnancies, i.e., oligohydramnios in 31 and polyhydramnios in 28 cases. Birth weight was below the tenth percentile in over half of the chromosomally abnormal fetuses, except for Turnersyndrome. Fetal outcome was poor, with a survival rate at 1 month of 30 per cent for trisomies which was mainly determined by trisomy 21 (14/18=77.5 per cent).     

Isolated choroid plexus cysts—the need for routine offer of karyotyping

The management of isolated fetal choroid plexus cysts remains controversial. We have prospectively studied 15 565 pregnancies at two large obstetric units for the presence of choroid plexus cysts. In all cases where cysts were present at 19 weeks' gestation or greater, and were multiple, bilateral or solitary and greater than 5 mm maximum diameter, women were offered amniocentesis or placental biopsy, irrespective of the presence or absence of other abnormalities. Choroid plexus cysts were present in 152 (0·98 per cent) of cases. Four cases (2·6 per cent) of autosomal trisomy (three of trisomy 18, one of trisomy 21) were detected on prenatal karyotyping. In all cases, choroid plexus cysts were the only detectable prenatal anomaly. This study and a review of other large studies do not support the view that isolated choroid plexus cysts are a benign variant, the risk of trisomy being 1 in 82. Until further evidence is available, we recommend that cases of isolated fetal choroid plexus cysts at 19 weeks' gestation or greater should be offered prenatal karyotyping.     

Maternal serum alpha-fetoprotein and fetal triploidy

Fetal triploidy is commonly found in early pregnancy. The majority of these pregnancies spontaneously abort in the first trimester. Occasionally, the pregnancy progresses to the second and third trimesters. We reviewed the maternal serum alpha-fetoprotein (MSAFP), amniotic fluid alpha-fetoprotein (AFP), amniotic fluid acetylcholinesterase (ACHE), fetal pathology, and placental pathology in sex second-trimester pregnancies complicated by fetal triploidy. Four of these patients had MSAFP values greater than 7.5 multiples of the median (MoM). Five of six pregnancies had MSAFP values greater than 2.25 MoM. All five of these patients had a partial mole. Four patients had amniotic fluid AFP values greater than 2.0 MoM. Two fetuses had associated neural tube defects. These were the only patients with positive amniotic fluid ACHE. None of the other patients had fetuses with anomalies that are known to be associated with an elevated MSAFP. The elevated MSAFP appeared to be related to the presence of a partial mole. Two of the five cases with an MSAFP greater than 2.25 MoM did not have sonographic evidence of a significant anomaly. Therefore, karyotyping can be of benefit in evaluating patients with elevated MSAFP.