Extra embryonic/fetal karyotypic discordance during diagnostic chorionic villus sampling

From a total of 1312 diagnostic chorionic villus samplings (CVS) there were 22 which showed discordance between the karyotype of the chorionic villi and that of the fetus. This frequency was some 20-fold higher than that reported at amniocentesis. In the majority of discordant cases, the fetal karyotype was normal while the placenta! karyotype was mosaic. In four cases, the placenta! karyotype was non-mosaic (a trisomy 16, a monosomy X, and two tetraploids) while the fetal karyotype was normal. In one case, the placenta was trisomy 18 while the fetus was mosaic. There were two ‘false-negative’ results where short-term methods showed only normal cells while both long-term cultures of chorionic villi and fetal cells were mosaic, in one 46,XY/47.XXY and in the other 46,X Y/47.X Y, + 21.     

Prenatal diagnosis and confirmation of infantile sialic acid storage disease

Amniocentesis was performed in a pregnancy at risk for infantile sialic acid storage disease. Greatly elevated levels of free sialic acid were found in cell-free amniotic fluid as well as in cultured amniotic cells from the fetus at risk. After incubation of the cultured amniocytes with fetuin labelled in its sialic acid moiety, pulse and chase experiments respectively showed accumulation and impaired release of TCA-soluble radioactive material in the amniotic cells at risk. These data thus clearly indicated that the fetus was affected. After pregnancy termination, ultrastructural studies of fetal organs and placenta showed a generalized storage picture characterized by clear membrane-bound inclusions. The diagnosis was further confirmed by the finding of greatly increased amounts of free sialic acid in fetal organs and cultured fibroblasts.     

Prenatal diagnosis of tetrasomy 12p by in situ hybridization: Varying levels of mosaicism in different fetal tissues

Prenatal diagnosis of tetrasomy 12p is complicated by the discrimination of the 12p isochromosome from the duplication 21q as well as the level of mosaicism demonstrated in the particular tissue sampled. In this disease, a high percentage of chromosomally abnormal cells are generally found in fibroblastic cells, but lymphocyte karyotypes from the same individual may be normal. We report on the pregnancy of a 37-year-old female who presented to our centre at 16 weeks' gestation for genetic amniocentesis. Sonography of the fetus revealed dextrocardia and diaphragmatic hernia. Chromosome analysis of amniocytes demonstrated mosaicism of a 47,XY,+i(12p) line in 80 per cent of cells and a normal male line (20 per cent), consistent with the Pallister-Killian syndrome. Following termination, a 220 g male fetus of 18 weeks was examined. A flattened nose and low-set ears were noted. In situ hybridization with a chromosome 12 centromeric probe in lymphocytes and skin cells unequivocally confirmed the karyotype and showed the presence of a single centromere in the abnormal chromosome, suggesting a true isochromosome. Chromosome analysis of various fetal tissues was performed and the following percentages of abnormal cells were found: skin 100 per cent, chorion 50 per cent, placenta 30 per cent, and blood 80 per cent. The high frequency of tetrasomic cells in fetal blood at this early gestational age is noteworthy, since most reports of this syndrome show a very low percentage of abnormal cells postnatally.     

A normal 46,XX infant with a 46,XX/ 69.XXY placenta: A major contribution to the placenta is from a resorbed twin

A predominantly triploid 69,XXY placenta was found associated with a normal 46,XX infant. Therefore, a triploid placenta is apparently capable of supporting normal fetal development. The chromosome and pathological results support the conclusion that the triploid placenta originates from a ‘vanishing twin’ pregnancy. This case is unusual in that persistence of the placenta from the vanished twin has virtually replaced most of the normal placenta.     

A revisit of trisomy 20 mosaicism in prenatal diagnosis—an overview of 103 cases

One hundred and three cases with prenatal diagnosis of trisomy 20 mosaicism through amniocentesis were reviewed. Approximately 90 per cent (90/101) of the cases were associated with grossly normal phenotype. It is likely that, in the majority of cases, cells with trisomy 20 were extraembryonic in origin or largely confined to the placenta. However, in some cases, the cells with trisomy 20 were confined to certain specific fetal organs or tissues such as kidney, skin, etc. Cytogenetic follow-up studies in liveborns should include a culture from urine sediment.     

Trisomic 22 placenta in a case of severe intrauterine growth retardation

We describe a case in which a trisomic 22 placenta could be the cause of severe growth retardation in a chromosomally normal female fetus. At amniocentesis a mosaic 46,XX/ 47,XX, +22 was observed in amniotic fluid specimens sampled on two different occasions, while fetal blood from a diagnostic cordocentesis revealed a normal chromosome constitution. Postnatal studies showed the consistent presence of trisomic 22 cells in the placenta, while only normal metaphases were found in amnion, blood, and fibroblast cultures.     

Body stalk anomaly associated with maternal cocaine abuse

A case of body stalk anomaly diagnosed prenatally by ultrasound during the 24th week of pregnancy in a cocaine abusing mother is presented. Accurate visualization of the fetal organs was difficult due to the severe oligohydramnios caused by premature rupture of membranes, probably related to the cocaine use. The sonographic findings were an omphalocoele, fetal attachment to the placenta, kyphoscoliosis, and absence of a floating umbilical cord. The prenatal diagnosis of the syndrome and the possible relationship with cocaine abuse are discussed.     

Prenatal diagnosis of trisomy 9 mosaicism possibly limited to fetal membranes

In repeat amniotic fluid cultures mosaicism due to trisomy 9 was noted. Autopsy of the aborted female fetus showed a sinus urogenitalis and gonadal dysgenesis with absence of germ cells only. Fetal lymphocytes and skin fibroblasts had a normal karyotype but trisomy 9 was found in cells grown from placenta. It is likely that trisomic cells were limited to fetal membranes.     

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.     

An embryogenic model to explain cytogenetic inconsistencies observed in chorionic villus versus fetal tissue

While the fetus and placenta have a common ancestry, chorionic villus tissue does not always reflect fetal genotype. Data are presented from 15 CVS subjects in whom cytogenetic inconsistencies were observed when comparing (1) cultured chorionic villi, (2) direct chromosome preparations of intact villi, and (3) cultured fetal tissue. Embryogenic models are presented to explain these discrepancies. Mosaicism confined to direct chromosome preparations was the most commonly observed inconsistency. This can be explained by postzygotic non-disjunction limited to cytotrophoblast. In all but one instance, the abnormal cell line was limited to the placenta, with the normal cell line reflecting fetal genotype. Analysis of direct chromosome preparations from multiple individually processed villus fragments may be helpful in recognizing mosaicism confined to the placenta. While both direct chromosome preparations and villus cultures can be misleading, the latter are more likely to reflect fetal genetic status since they are derived from the extraembryonic mesoderm.     

Complex karyotypic mosaicism as a result of non-disjunction and subsequent centromere fission

Karyotypic discrepancy among four different cell types is described in tissues derived from a pregnancy terminated because of chromosomal anomalies. Chorionic villus cells demonstrated 46,XX (direct preparation) and 46, XX/47,XX,+marl (cultured cells) karyotypes, while fetal skin fibroblasts had a karyotype of 47,XX,+ 18 and the placenta showed a triple mosaicism of 47,XX, + 18/47,XX,+mar1/48,XX,+ 18,+mar2. The origin of this complex chromosomal distribution and its significance are discussed in comparison with findings in similar cases.     

First-trimester maternal serum alphafetoprotein and chorionic gonadotropin in aneuploid pregnancies

First-trimester maternal serum alpha-fetoprotein (AFP) and human chorionic gonadotropin (HCG) levels were measured in samples from 29 women with cytogenetically abnormal pregnancies and 145 women with cytogenetically normal pregnancies matched for gestational age, race, and sample storage time. All patients had a risk of fetal aneuploidy greater than or equal to that of a mother 35 years of age. AFP was significantly lower in samples from pregnancies affected with trisomy 21 (0.67 MoM;p <0.05), while HCG values were no different from those of matched controls. Trisomies 13 and 18 could not be distinguished from matched controls by AFP. However, levels of HCG were significantly lower in such pregnancy samples, with median values of 0.65 MoM in trisomy 13 and 0.32 MoM in trisomy 18 (p<0.05). Variations in AFP and HCG levels suggest that expressed differences between autosomal aneuploidies include differences in fetal and placenta! protein production in the first trimester.     

46,XY/47,XY,+ 17p+ mosaicism in amniocytes associated with fetal abnormalities despite normal fetal blood karyotype

46,XY/47,XY, + 17p + mosaicism was found in two primary amniotic fluid cultures (AFCs). Fetal blood karyotype was normal, but ultrasonography revealed Dandy-Walker malformation and bilateral choroid plexus cysts. Following termination of pregnancy, fetal examination revealed post-axial polydactyly and neuroblastoma-in-situ affecting both adrenals in addition to the cerebellar abnormalities. Mosaicism for the aberrant cell line was confirmed in all fetal tissues sampled and in the placenta.     

Prenatal diagnosis and post-mortem study of a fetus with mosaic trisomy 14 due to a dic(14)(p11)

Amniocentesis at 17 weeks' gestation revealed a mosaic karyotype—46,XX/46,XX, — 14,+dic(14)(p11). No abnormalities were detected on ultrasound. Growth and placentation were normal. The fetus was examined after termination of pregnancy and micrognathia and pulmonary hyperlobation were the only abnormalities detected. Several tissues were set up for cytogenetics, including fetal skin, kidney, ovary, and placenta. The diagnosis was confirmed by these studies. The level of mosaicism varied between tissues, with the trisomy 14 cell line highest in amniotic fluid.     

Trisomy 7 in chorionic villi: Follow-up studies of pregnancy,normal child,and placental clonal anomalies

Cytogenetic study of chorionic villi sampled because of advanced maternal age revealed, after overnight culture, an apparently non-mosaic trisomy 7. Amniocentesis showed exclusively normal mitoses, and the pregnancy continued normally. One hundred mitoses from cord blood of the normal newborn revealed a non-mosaic 46,XX complement. No cells with a proven trisomy 7 were found in cultures from either of two biopsies of the morphologically normal placenta, but the peripheral biopsy showed in multiple cultures an abnormal clone: 47,XX, + 20,-2,-21, + t(2;21)(p13;q22). To our knowledge, this is the first case of non-mosaic trisomy 7 detected on CVS which has had follow-up studies of amniotic fluid, cord blood, and term placenta.     

The ductus venosus in early pregnancy and congenital anomalies

The ductus venosus (DV) is a tiny vessel leading oxygenated blood from the placenta to the fetal heart and its flow assessment has been used as an indicator of fetal acidemia. At 11 to 14 weeks, the fetuses with increased nuchal translucency also showing an abnormal DV blood flow were consistently found to be aneuploid. Early cardiac dysfunction, signaled by abnormal DV blood flow, was suggested as the underlying cause of increased nuchal translucency. Detection rates for aneuploidy with the use of DV blood flow studies range from 59 to 93% with 2 to 21% false-positive rates. In fetuses with normal karyotype, an abnormal DV flow pattern signals cardiac defects or adverse perinatal outcome. Copyright © 2004 John Wiley & Sons, Ltd.     

Placental mosaicism in a case of 46,XY, −22, +t(22;22)(p11;q11) or i(22q) diagnosed at amniocentesis

46,XY, −22,+t(22;22)(p11;q11) or i(22q) was diagnosed in 15/15 cells from two cultures from the amniotic fluid culture of a 31-year-old patient whose fetus demonstrated cystic hygroma on ultrasound. Cytogenetic studies performed on fetal skin from the abortus revealed the same karyotype as that seen on amniocentesis, but the placenta demonstrated a 46,XY,46,XY, −22,+t(22;22) or i(22q) mosaicism, with 65 per cent of the cells being 46,XY. This case provides an example of placental mosaicism for a normal male karyotype, while the fetus demonstrated non-mosaic trisomy 22.     

Maternal platelet size as a marker for fetal trisomies 18 and 13

Maternal and fetal platelet size and glycoprotein expression were measured in 14 pregnancies complicated by fetal aneuploidy between 20 and 24 weeks' gestation. Flow cytometry was used to determine platelet size and surface glycoprotein Ib (GPIb) and GPIIIa expression both before and after stimulation with adenosine diphosphate (ADP). The data were compared with results obtained from 35 normal paired maternal and fetal controls. In fetuses affected with trisomies 18 and 13, but not trisomy 21, the maternal and fetal platelet sizes were significantly higher than those of the normal controls. Furthermore, the increase in fetal platelet size was significantly associated with the increase in maternal platelet size. Increase in maternal platelet size may be of potential value as a marker for fetal trisomies 18 and 13.     

The impact of maternal plasma DNA fetal fraction on next generation sequencing tests for common fetal aneuploidies

Maternal plasma contains circulating cell-free DNA fragments originating from both the mother and the placenta. The proportion derived from the placenta is known as the fetal fraction. When measured between 10 and 20 gestational weeks, the average fetal fraction in the maternal plasma is 10% to 15% but can range from under 3% to over 30%. Screening performance using next-generation sequencing of circulating cell-free DNA is better with increasing fetal fraction and, generally, samples whose values are less than 3% or 4% are unsuitable. Three examples of the clinical impact of fetal fraction are discussed. First, the distribution of test results for Down syndrome pregnancies improves as fetal fraction increases, and this can be exploited in reporting patient results. Second, the strongest factor associated with fetal fraction is maternal weight; the false negative rate and rate of low fetal fractions are highest for women with high maternal weights. Third, in a mosaic, the degree of mosaicism will impact the performance of the test because it will reduce the effective fetal fraction. By understanding these aspects of the role of fetal fraction in maternal plasma DNA testing for aneuploidy, we can better appreciate the power and the limitations of this impressive new methodology. © 2013 John Wiley & Sons, Ltd.     

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.