Non-mosaic trisomy 20 in amniotic fluid cultures with minor anomalies in the fetus

A non-mosaic trisomy 20 was discovered in all cells in two separate cultures from an age-related genetic amniocentesis. Karyotypes of cells obtained via amniocentesis at the time of termination and of cells cultured from the placenta gave the same unambiguous results. However, the fetus, under macro- and microscopic analysis, showed only two minor anomalies: left simian crease and low-set ears. These findings are more suggestive of a normal or at most mosaic trisomy 20 state. The significance of this finding for prenatal diagnosis is discussed.     

Two cases of 8p trisomy in one sibship

Two cases of 8p trisomy in one sibship are presented. The father was a balanced carrier of a translocation rep (8;13) (p11; q34). Case 1 was a 2-year-old boy with multiple minor anomalies and severe mental retardation. Giemsa banding studies revealed that he was trisomic for the greater part of 8p (8p11 → pter). When his mother became pregnant again, amniocentesis was carried out in the 17th week of gestation. The fetus (Case 2) was shown to have the same 8p trisomy as Case 1. The pregnancy was terminated in the 22nd week. An autopsy revealed no major anomalies. Clinical features of cases with 8 and 8p trisomy are reviewed briefly.     

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. Am. J. Med. Genet. 72:343–346, 1997. © 1997 Wiley-Liss, Inc.     

Prenatal diagnosis of mosaic trisomy 8q studied by ultrasound, cytogenetics, and array-CGH

Mosaic trisomy 8, also known as Warkany syndrome, has a well-characterized constellation of phenotypic findings. Partial trisomy 8, including mosaic cases, has also been reported, with outcome and counseling dependent on the chromosomal segment involved and whether accompanied by partial aneuploidy for other chromosomes. We present a case of a fetus mosaic for trisomy of the entire long arm (q) of chromosome 8 without additional chromosomal aberrations. The diagnosis was made by amniocentesis performed following an 18 week sonogram that showed multiple fetal anomalies. Mosaicism for trisomy 8q was confirmed by routine karyotyping and fluorescent in situ hybridization (FISH) analysis. The case proved useful for testing the sensitivity of array comparative genomic hybridization (array-CGH) with respect to segmental trisomy in the presence of chromosomal mosaicism. The phenotype of this fetus, which appears to be the first reported case involving mosaic trisomy 8 for the entire q arm of the chromosome, is described and compared to previously reported cases involving partial trisomy 8q.     

Double aneuploidy involving trisomy 7 with Potter sequence

We report a prenatal case of double aneuploidy (consisting of chromosome 7 and X) with the features of Potter sequence. Of the stillborn fetus, skin fibroblast cultures were performed and fluorescence in situ hybridization (FISH) technique was also used for further investigation. On physical examination; the fetus was found to have malformed ears, micrognatia, hypertelorism, abnormal extremities, rocker-bottom feet and abnormal external genitalia and polycystic right kidney was seen after an extensive autopsy. As amniocentesis and cordocentesis materials revealed X chromosome mosaicism, trisomy 7 was detected in the skin fibroblast culture of the ex fetus and karyotype evaluated as composite; 46~47,X,+7,-X[cp18]. FISH results confirmed the double aneuploidy and also revealed XX and XXXX cell lines. Comparison with the previously reported cases of trisomy 7 with Potter syndrome suggests a possible link (if not coincidental) between trisomy 7 and Potter syndrome in our case. This is the first reported case of double aneuploidy involving trisomy 7 with the features of Potter syndrome.     

Trisomy 5 mosaicism in amniotic fluid with normal outcome

A case of prenatally diagnosed true mosaicism for trisomy 5 with a clinically normal outcome is presented. Trisomy 5 was detected in 23% of cells obtained by amniocentesis, but it was not detected from cells obtained by fetal blood sampling. While in this case the finding at amniocentesis did not reflect the status of the fetus, care must be exercised in reaching this conclusion in all cases.     

Trisomy 7 mosaicism prenatally misdiagnosed and maternal uniparental disomy in a child with pigmentary mosaicism and Russell- Silver syndrome

Prenatal diagnosis of true mosaic trisomy 7 is rare in amniotic fluid and can be misinterpreted as pseudomosaic. The phenotype is highly variable and may be modified by a maternal uniparental disomy of chromosome 7 leading to mild Russell-Silver syndrome (RSS). We report here the third postnatal case of mosaic trisomy 7 with maternal uniparental disomy of chromosome 7 in a boy presenting a mild RSS. Fetal karyotype performed in amniocentesis for intrauterine growth retardation was considered normal. Mosaic trisomy 7 was diagnosed after birth, on fibroblasts karyotype performed for blaschkolinear pigmentary skin anomalies and failure to thrive. Maternal uniparental disomy of chromosome 7 was observed in blood sample. Retrospectively, trisomic 7 cells were identified in one prenatal long-term flask culture revealing a prenatal diagnosis failure. This report emphasizes the difficulty of assessing fetal mosaicism and distinguishing it from pseudomosaicism in cultured amniocytes. It is important to search for uniparental disomy as an indirect clue of trisomy 7 mosaicism and a major prognosis element. Although there are only few prenatal informative cases, detection of trisomy 7 in amniocentesis appears to be associated with a relatively good outcome when maternal uniparental disomy has been ruled out.     

Paternal normal/trisomy 21 mosaicism as an indication for amniocentesis

Normal/trisomy 21 mosaicism was demonstrated in the father of a girl with Down's syndrome. During the next pregnancy, amniocentesis and karyotyping of the fetus were conducted. The fetus proved to be healthy.     

Non-mosaic uniparental trisomy 16 presenting with asplenia syndrome and placental abruption: A case report and literature review

Non-mosaic trisomy 16 is rarely seen in later gestation. Herein, we report a fetus with uniparental complete trisomy 16 manifesting with asplenia syndrome, left hand deformity (only 3 deformed fingers on the left hand) and a left low-set ear. The pregnancy ended in severe placental abruption and resultant fetal demise, and maternal hypovolemic shock at 35 weeks of gestation. Only 3 non-mosaic trisomy 16 fetuses, including this case, have been reported to survive into the second or third trimester. Furthermore, this fetus would be the first case of complete trisomy 16 manifesting as asplenia syndrome.     

羊水细胞学检查在产前诊断中的应用

目的：分析产前诊断的高危孕妇羊水细胞染色体核型,了解孕中期异常核型出现的频率,类型及与各种产前诊断指征之间的关系。方法：130例有产前论断孕妇（2例为双胎妊娠）在妊娠17－27周时行羊膜腔穿刺术,抽羊水行羊水细胞培养查染色体核型。结果：羊水细胞培养成功并进行核型分析的为126例,成功率为95．4％;妊17－20周与妊20－27周的羊水培养成功率未见显著差异,分别95．9％（71／74）,94．8％（55／58）,P＞0．05;发现异常核型10例,异常检出率为7．8％（10／126）;三体为主要的染色体异常,占异常核型的40％（4／10）,其中21三体占30％（3／10）,性染色体数目异常及平衡易位各1例,4例INV9;畸胎为指征的异常核型检出率高达33．3％（2／6）;发现1例单卵双胎妊娠两胎均为21三体儿;高龄为指征占成功产前诊断的46．3％（60／126）,检出异常核型3例,检出率5％（3／60）。结论：在有产前诊断指征的孕妇中,胎儿染色体异常核型的发生率为7．8％,三本仍是妊娠中期主要的异常核型,结合B超筛查及定位的羊膜腔穿刺术在产前诊断仍占有不可代替的重要作用。     

Screening for fetal Down's syndrome in pregnancy by measuring maternal serum alpha-fetoprotein levels

Although the risk of Down's syndrome increases with maternal age, women under 35 bear about 80 percent of the infants born with this condition. We prospectively investigated the utility of measuring maternal serum alpha-fetoprotein during the second trimester in women under 35 in order to identify pregnancies in which the fetus was affected with Down's syndrome. Over a two-year period, 34,354 women in this age group were screened. Amniocentesis was offered when the risk of Down's syndrome, calculated as a function of maternal age and maternal serum alpha-fetoprotein concentration adjusted for maternal weight and race, was 1:270 or higher, the risk for a 35-year-old woman. This threshold was exceeded in 1451 women in whom gestational age was confirmed by ultrasound; 9 women in this group had a fetus with the syndrome. In three women whose fetuses had trisomy 18 and one whose fetus had trisomy 13, the calculated risk of Down's syndrome was 1:270 or higher. Thus, among women in whom the risk exceeded our cutoff point, 1 in 161 were found to have a pregnancy in which the fetus was affected with Down's syndrome; the figure was 1 in 112 for all autosomal trisomies. Eighteen pregnancies involving Down's syndrome, three involving trisomy 18, and two involving trisomy 13 were not associated with a calculated risk above the cutoff point. The available data indicate that in our population, using a cutoff for risk at which 5 percent of women under 35 are offered amniocentesis, we will detect one quarter to one third of pregnancies in which the fetus has Down's syndrome.     

Sex determination,differentiation and intersexuality in placental mammals. By R. H. F. Hunter. Cambridge: Cambridge University Press, 1995, pp 310

We have reported previously a 10% aneuploidy detection rate among 39 cases of fetal neural tube defects (NTD). Subsequently we amassed an additional experience of over 17,000 prenatal diagnosis cases over a 5-year period. During this period 106 cases of NTDs were identified; 44 with anencephaly, 62 with open spina bifida. The average maternal age of this population with NTDs was 29 years (15–40); 6 patients declined amniocentesis. Six of 100 cytogenetic studies were aneuploid; one anencephalic fetus had inherited a maternal marker chromosome, and 5 NTD cases had trisomy 18. The average maternal age of the aneuploid cases was 31 (19–40); 3 were 35 years or older. Four of 5 trisomy 18 cases had multiple congenital anomalies (MCA). The overall aneuploidy detection rate in our cohort was 5–6%, while aneuploidy occurred in 2% of the isolated NTD cases, and 24% of the MCA cases. Combining the earlier experience, 4/39 aneuploidy (2 trisomy 18, 4p+, del 13q) yields an aneuploidy detection frequency of 10/145 (7%), of which most (7/10) had trisomy 18. These data support fetal karyotyping for accurate diagnosis, prognosis, and recurrence-risk counseling. © 1996 Wiley-Liss, Inc.     

European collaborative research on mosaicism in CVS (EUCROMIC)—fetal and extrafetal cell lineages in 192 gestations with CVS mosaicism involving single autosomal trisomy

Cytogenetic information on cells from cytotrophoblast, villus mesenchyme, and one or more fetal tissues was available for 192 gestations with mosaicism or non-mosaic fetoplacental discrepancy involving a single autosomal trisomy in the chorionic villus sample (CVS), registered in a collaborative study (EUCROMIC) during the period 1986–1994. In order to identify predictors of confined placental mosaicism (CPM), generalized mosaicism and/or uniparental disomy (UPD), distribution of the mosaic and non-mosaic aneuploid cell lines in the different fetal and extrafetal cell lineages were analyzed. Data were related to existing hypotheses on mechanisms leading to fetoplacental discrepancies and early extraembryonic cell differentiation. Trisomy 21 mosaicism was the one most frequently confirmed in the fetus. Non-mosaic trisomy 13, 18, and 21 in the villus mesenchyme indicated the presence of a trisomic cell line in the fetus proper. Non-mosaic trisomy 2, 7, and 16 in villus mesenchyme was always found with concomitant mosaic or non-mosaic trisomy in the cytotrophoblast, but was never recovered in the fetus. Mosaic trisomy 3, 7, and 20 was predominantly restricted to the cytotrophoblast, mosaic trisomy 2 to the villus mesenchyme. Trisomies 15 and 16 were most often found in both cytotrophoblast and villus mesenchyme and not in fetal cells. This supports the hypothesis that mosaicism/discrepancy for trisomies 15 and 16 results more often than for the other trisomies from trisomic zygote rescue, enhancing their risk for UPD. We recommend, due to the risk of fetal trisomy, amniocentesis in all gestations involving mosaic autosomal trisomy in villus mesenchyme. In gestations with mosaic or non-mosaic autosomal trisomy in both cytotrophoblast and villus mesenchyme we recommend, in order to exclude fetal trisomy and/or UPD, depending on the chromosome involved, further examination by amniocentesis, ultrasound and/or test for UPD. We also recommend, due to a small but not negligible risk of false negative and false positive diagnoses, not to solely use direct preparation. Am. J. Med. Genet. 70:179–187, 1997. © 1997 Wiley-Liss, Inc.     

Partial trisomy 19p: case report and natural history

Partial trisomy 19p was noted in an infant delivered at 39 weeks gestation with intrauterine growth retardation (IUGR), bilateral club feet, renal abnormalities, hearing deficit, and multiple dysmorphic features. Chromosomes obtained following amniocentesis at 32 weeks gestation revealed that the fetus was partially trisomic for 19p and partially monosomic for a portion of the terminal band of 3q, having inherited a derivative chromosome 3 from her father [46,XX,-3,+der(3)t(3;19)(q29;p13.2)pat]. The father was found to be the carrier of a balanced translocation between chromosomes 3 and 19 [46,XY,t(3;19)(q29;p13.2)]. The only other case of partial trisomy 19p previously reported was an infant with partial trisomy 19p and partial monosomy 13q who died at 59 days of age. This report by Byrne et al. [(Am J Hum Genet 1980: 32:64A] is similar to our case with respect to IUGR, small palpebral fissures, and ear anomalies.     

Prenatal detection of double aneuploidy trisomy 10/monosomy X in a liveborn twin with exclusively monosomy X in blood

Both double aneuploidy and trisomy 10 are rare chromosome findings. All five published cases of trisomy 10 in liveborns were found to be mosaic with an euploid cell line. In a liveborn female twin, double aneuploidy mosaicism 47,XX, + 10/45,X was detected prenatally by amniocentesis performed because of severe intrauterine growth retardation and malformations. Chromosome analysis from neonatal lymphocyte cultures revealed exclusively the 45,X cell line. Double aneuploidy mosaicism trisomy 10/monosomy X was confirmed from skin fibroblasts. The child died at the age of 7 weeks. This is the first reported case of double aneuploidy involving trisomy 10, and the first case of trisomy 10 without a normal cell line in a liveborn. Prenatal diagnosis of trisomy 10 in a liveborn has not been published so far. The case illustrates that in specific cases amniotic fluid cells may reflect the karyotype of the fetus better than blood.     

Prenatal diagnosis of low level trisomy 15 mosaicism: review of the literature

Low level chromosome mosaicism found at amniocentesis is problematic for clinicians and patients. We report prenatal diagnosis of a fetus with a rare karyotype of 47.XX, + 15/46, XX. Second trimester amniocentesis was performed for advanced maternal age. Fetal ultrasound revealed a hypoplastic right ventricle and intrauterine growth retardation (IUGR). The rest of the fetal anatomy was within normal limits. A mosaic karyotype of 47.XX, + 15/46, XX was observed. The couple interrupted the pregnancy at 19 weeks by dilation and suction evacuation. Careful evaluation of multiple pieces of fetal parts and placenta revealed one abnormal finding: a single umbilical artery. Cytogenetic metaphase and fluorescent in situ hybridization (FISH) interphase analyses of cells from fetal lung, heart, placenta, and skin revealed the presence of the trisomic line in all tissues. Molecular analysis demonstrated that the origin of the extra chromosome 15 was maternal, the error most likely occurred in meiosis I and the diploid line was of biparental inheritance. This case report discusses the associated findings in this fetus and reviews the literature describing other cases of mosaic trisomy 15.     

Chromosome mosaicism in 6,000 amniocenteses

Multiple cell-multiple flask mosaicism was found in 0.20% of 6,000 amniocenteses, and multiple cell-single flask mosaicism was found in 0.92%. Multiple cell-multiple flask mosaicism usually was found in fetal or infant tissues at delivery or elective abortion. Most multiple cell-multiple flask mosaicism involved sex chromosomes and was either 45, X/46, XY or 45, X/46, XX. Except for one fetus with 45, X/46, XX and an aortic coarctation, phenotypic abnormalities associated with sex chromosome mosaicism were not found in these patients. One normal boy has continued to show 45,X mosaicism during the first 4 years of life. Autosome abnormalities found in multiple cell-multiple flask mosaicism included del(18q) associated with fetal anomalies. Apparently normal phenotypes were associated with prenatal trisomy 17, two de novo supernumerary marker chromosomes, and monosomy 21. Since an aberrant cell line present in only one primary amniotic fluid cell culture was occasionally identified from another amniocentesis or at birth, multiple cell-single flask mosaicism involving a sex chromosome or a viable autosome abnormality cannot be assumed to be an in vitro event. Maternal cell contamination, which was found in 0.49% of amniocenteses, could have resulted in an erroneous diagnosis of fetal sex in two cases if cells from independent culture vessels were not examined.     

Spontaneous deaths of fetuses with chromosomal abnormalities diagnosed prenatally.

In a survey of pregnancies, in which a chromosomal abnormality was diagnosed by amniocentesis but in which the mother did not undergo an abortion, the spontaneous fetal death rate after amniocentesis for 21 fetuses with Down's syndrome was 24 per cent (or 21 per cent, considering 19 singletons only). This rate is significantly greater than the rate of 2.7 per cent among 73 fetuses with less seriously abnormal genotypes reported in this survey or of 3.3 per cent and 3.5 per cent in the Canadian and United States studies of amniocentesis. After midtrimester there is about a sixfold higher risk of spontaneous fetal death for a fetus with Down's syndrome than for one with a normal genotype. At least some (and probably a major fraction) of the discrepancy observed between maternal-age-specific rates of Down's syndrome in live births and those found after amniocentesis is due to spontaneous fetal loss. A similar inference may be drawn for trisomy 18.     

A chromosome 21-derived minute marker in a mosaic trisomy 21 background: implications for risk assessments in marker chromosome cases

We report a prenatal case of a chromosome 21-derived minute supernumerary marker, found as a mosaic along with a trisomy 21 cell line at amniocentesis. Follow-up analysis of other fetal tissues confirmed the mosaicism and also disclosed a normal cell line. It is likely that the marker reflects a mutation event that resulted in trisomy rescue early in embryonic development. Had the trisomy 21 cell line not been found at amniocentesis, a low risk of an abnormal phenotype (approximately 5%) would have been assigned. We suggest that the risk associated with minute non-euchromatic marker chromosomes should be revised to account for the possibility of mosaicism with potentially aneuploid populations and/or uniparental disomy (UPD). The finding of any marker chromosome should prompt a thorough investigation for aneuploid cell lines. In the case of small markers with no euchromatin, the given risk of adverse phenotypic effects is not likely to be associated with the marker per se but with the possible presence of a cryptic aneuploid cell line from which the marker may have arisen.