Prenatally detected trisomy 20 mosaicism

Clinical outcomes of screen-positive genome-wide cfDNA cases for trisomy 20: results from the global expanded NIPT Consortium

Trisomy 20 has been shown to be one of the most frequent rare autosomal trisomies in patients that undergo genome-wide noninvasive prenatal testing. Here, we describe the clinical outcomes of cases that screened positive for trisomy 20 following prenatal genome-wide cell-free (cf.) DNA screening. These cases are part of a larger cohort of previously published cases. Members of the Global Expanded NIPT Consortium were invited to submit details on their cases with a single rare autosomal aneuploidy following genome-wide cfDNA screening for retrospective analysis. Clinical details including patient demographics, test indications, diagnostic testing, and obstetric pregnancy outcomes were collected. Genome-wide cfDNA screening was conducted following site-specific laboratory procedures. Cases which screened positive for trisomy 20 (n = 10) were reviewed. Clinical outcome information was available for 90% (9/10) of our screen-positive trisomy 20 cases; the case without diagnostic testing ended in a fetal demise. Of the nine cases with outcome information, one was found to have a mosaic partial duplication (duplication at 20p13), rather than a full trisomy 20. Only one case in the study cohort had placental testing; therefore, confined placental mosaicism could not be ruled out in most cases. Adverse pregnancy outcomes were seen in half of the cases, which could suggest the presence of underlying confined placental mosaicism or mosaic/full fetal trisomy 20. Based on our limited series, the likelihood of true fetal aneuploidy is low but pregnancies may be at increased risk for adverse obstetric outcomes and may benefit from additional surveillance.

Prenatal diagnosis of mosaic chromosomal aneuploidy and uniparental disomy and clinical outcomes evaluation of four fetuses

BACKGROUND

Few co-occurrence cases of mosaic aneuploidy and uniparental disomy (UPD) chromosomes have been reported in prenatal periods. It is a big challenge for us to predict fetal clinical outcomes with these chromosome abnormalities because of their highly heterogeneous clinical manifestations and limited phenotype attainable by ultrasound.

METHODS

Amniotic fluid samples were collected from four cases. Karyotype, chromosome microarray analysis, short tandem repeats, and whole exome sequencing were adopted to analyze fetal chromosomal aneuploidy, UPD, and gene variation. Meanwhile, CNVseq analysis proceeded for cultured and uncultured amniocytes in case 2 and case 4 and MS-MLPA for chr11 and chr15 in case 3.

RESULTS

All four fetuses showed mosaic chromosomal aneuploidy and UPD simultaneously. The results were: Case 1: T2(7%) and UPD(2)mat(12%). Case 2: T15(60%) and UPD(15)mat(40%). Case 3: 45,X(13%) and genome-wide paternal UPD(20%). Case 4: <10% of T20 and > 90% UPD(20)mat in uncultured amniocyte. By analyzing their formation mechanism of mosaic chromosomal aneuploidy and UPD, at least two adverse genetic events happened during their meiosis and mitosis. The fetus of case 1 presented a benign with a normal intrauterine phenotype, consistent with a low proportion of trisomy cells. However, the other three fetuses had adverse pregnancy outcomes, resulting from the UPD chromosomes with imprinted regions involved or a higher level of mosaic aneuploidy.

CONCLUSION

UPD is often present with mosaic aneuploidy. It is necessary to analyze them simultaneously using a whole battery of analyses for these cases when their chromosomes with imprinted regions are involved or known carriers of a recessive allele. Fetal clinical outcomes were related to the affected chromosomes aneuploidy and UPD, mosaic levels and tissues, methylation status, and homozygous variation of recessive genes on the UPD chromosome. Genetic counseling for pregnant women with such fetuses is crucial to make informed choices.

Clinical utility of chromosomal microarray analysis and whole exome sequencing in foetuses with oligohydramnios

OBJECTIVES

To evaluate the clinical utility of chromosomal microarray analysis (CMA) and whole exome sequencing (WES) in foetuses with oligohydramnios.

METHODS

In this retrospective study, 126 fetuses with oligohydramnios at our centre from 2018 to 2021 were reviewed. The results of CMA and WES were analysed.

RESULTS

One hundred and twenty-four cases underwent CMA and 32 cases underwent WES. The detection rate of pathogenic/likely pathogenic (P/LP) copy number variant (CNV) by CMA was 1.6% (2/124). WES revealed P/LP variants in 21.8% (7/32) of the foetuses. Six (85.7%, 6/7) foetuses showed an autosomal recessive inheritance pattern. Three (42.9%, 3/7) variants were involved in the renin-angiotensin-aldosterone system (RAAS), which are the known genetic causes of autosomal recessive renal tubular dysgenesis (ARRTD).

CONCLUSION

CMA has low diagnostic utility for oligohydramnios, while WES offers obvious advantages in improving the detection rate. WES should be recommended for fetuses with oligohydramnios.

Low-level mosaic trisomy 20 without uniparental disomy 20 at amniocentesis in a pregnancy associated with a favorable outcome, cytogenetic discrepancy between uncultured amniocytes and cultured amniocytes and perinatal progressive decrease of the aneuploid cell line

OBJECTIVE

We present low-level mosaic trisomy 20 without uniparental disomy (UPD) 20 at amniocentesis in a pregnancy associated with a favorable outcome, cytogenetic discrepancy between uncultured amniocytes and cultured amniocytes and perinatal progressive decrease of the aneuploid cell line.

CASE REPORT

A 36-year-old, gravida 2, para 1, woman underwent amniocentesis at 16 weeks of gestation because of advanced maternal age. Amniocentesis revealed a karyotype of 47,XY,+20[3]/46,XY[17]. Array comparative genomic hybridization (aCGH) analysis on the DNA extracted from uncultured amniocytes revealed the result of arr (1-22) × 2, X × 1, Y × 1 with no genomic imbalance. Prenatal ultrasound was unremarkable. She was referred for genetic counseling at 23 weeks of gestation, and repeat amniocentesis was performed. Cytogenetic analysis of the cultured amniocytes revealed a karyotype of 47,XY,+20[1]/46,XY[27]. Simultaneous aCGH analysis on the DNA extracted from uncultured amniocytes by SurePrint G3 Unrestricted CGH ISCA v2, 8 × 60 K (Agilent Technologies, CA, USA) revealed the result of arr (1-22) × 2, X × 1, Y × 1. Quantitative fluorescent polymerase chain reaction (QF-PCR) assays on the DNAs extracted from uncultured amniocytes and parental bloods excluded UPD 20. The woman was advised to continue the pregnancy, and a healthy 3750-g phenotypically normal male baby was delivered at 38 weeks of gestation. The cord blood had a karyotype of 46,XY (40/40 cells).

CONCLUSION

Low-level mosaic trisomy 20 without UPD 20 at amniocentesis can be associated with a favorable outcome. Progressive decrease of the aneuploid cell line can occur in mosaic trisomy 20 at amniocentesis. Low-level mosaic trisomy 20 at amniocentesis can be a transient and benign condition.

Prenatal diagnosis of pseudomosaicism for trisomy 20 at amniocentesis with a negative non-invasive prenatal testing (NIPT) result in a pregnancy with a favorable outcome

OBJECTIVE

We present prenatal diagnosis of pseudomosaicism for trisomy 20 at amniocentesis with a negative non-invasive prenatal testing (NIPT) result in a pregnancy with a favorable outcome.

CASE REPORT

A 33-year-old, primigravid woman underwent amniocentesis at 17 weeks of gestation, which revealed a karyotype of 47,XX,+20[8]/46,XX[31]. Simultaneous array comparative genomic hybridization (aCGH) analysis on the DNA extracted from uncultured amniocytes revealed the result of arr (1-22,X) × 2, consistent with no genomic imbalance. She was referred to the hospital for repeat amniocentesis at 23 weeks of gestation. At repeat amniocentesis, cultured amniocytes had a karyotype of 47,XX,+20[2]/46,XX[33]. The parental karyotypes were normal. Simultaneous aCGH analysis on the DNA extracted from uncultured amniocytes using SurePrint G3 Unrestricted CGH ISCA v2, 8 × 60 K (Agilent Technologies, Santa Clara, CA, USA) revealed no genomic imbalance, or arr (1-22,X) × 2, Y × 0. Interphase fluorescence in situ hybridization (FISH) analysis using the bacterial artificial chromosome (BAC) probes of RP11-266K16 [20q13.33; fluorescein isothiocyanate (FITC), spectrum green] and RP11-348I14 (20q11.1-q11.21; Texas Red, spectrum red) detected trisomy 20 signals in 4/104 uncultured amniocytes (3.8%), compared with 0/100 in the normal control. Polymorphic DNA marker analysis using the DNA extracted from uncultured amniocytes and parental bloods excluded uniparental disomy 20. NIPT analysis on maternal blood revealed a negative result without gene dosage increase in chromosome 20. The pregnancy was carried to term, and a healthy 2830-g female baby was delivered with no phenotypic abnormality. Both cord blood and placenta had a karyotype of 46,XX.

CONCLUSION

NIPT is useful for rapid differential diagnosis of pseudomosaicism from true mosaicism in case of mosaic trisomy 20 at amniocentesis.

Cytogenetic discrepancy between cultured amniocytes and uncultured amniocytes in mosaic trisomy 20 at amniocentesis in a pregnancy with a favorable outcome

OBJECTIVE

We present our observation of cytogenetic discrepancy between cultured amniocytes and uncultured amniocytes in mosaic trisomy 20 at amniocentesis in a pregnancy with a favorable outcome.

CASE REPORT

A 35-year-old woman underwent amniocentesis at 16 weeks of gestation because of advanced maternal age. Amniocentesis revealed a karyotype of 47,XX,+20[10]/46,XX[15]. Among 25 colonies of cultured amniocytes, 10 colonies had a karyotype of 47,XX,+20, while the rest were normal. Simultaneous array comparative genomic hybridization (aCGH) analysis on the DNA extracted from uncultured amniocytes revealed no genomic imbalance, or arr (1-22,X) × 2. The parental karyotypes were normal. Following genetic counseling, the woman underwent repeat amniocentesis at 20 weeks of gestation. Repeat amniocentesis revealed a karyotype of 47,XX,+20[3]/46,XX[35]. Among 38 colonies of cultured amniocytes, three colonies had a karyotype of 47,XX,+20, while the rest were normal. Simultaneous aCGH analysis on the DNA extracted from uncultured amniocytes revealed no genomic imbalance, or arr (1-22,X) × 2. Interphase fluorescence in situ hybridization analysis on 101 uncultured amniocytes detected only one cell with three chromosome 20 signals with a mosaic trisomy 20 level of 1% (1/101 cells), compared with 0% in normal control. Polymorphic DNA marker analysis on the DNA extracted from uncultured amniocytes and parental bloods excluded uniparental disomy 20. At 38 weeks of gestation, a phenotypically normal 3120-g female baby was delivered. Cytogenetic analysis of cord blood, placental tissue and umbilical cord revealed a karyotype of 46,XX. The neonate was normal at postnatal follow-ups. Postnatal interphase fluorescence in situ hybridization analysis on 100 buccal mucosal cells revealed no trisomy 20 signals.

CONCLUSION

Mosaic trisomy 20 at amniocentesis can be a cultured artifact. Complete cytogenetic discrepancy may occur between cultured amniocytes and uncultured amniocytes in mosaic trisomy 20 at amniocentesis, and molecular cytogenetic analysis on uncultured amniocytes is useful for rapid distinguishing true mosaicism from pseudomosaicism under such as circumstance.

A rare case of postnatal mosaic trisomy 12 with severe congenital heart disease and literature review

Trisomy 12 is a rare autosomal aneuploidy. All postnatally diagnosed individuals with trisomy 12 have been mosaic for this chromosome abnormality. We herein report an infant girl presented at 2 weeks of age with severe congenital heart defect, tracheobronchomalacia, and dysmorphic features. All of the dysmorphic features of this patient fit into the known phenotype spectrum of mosaic trisomy 12, although this patient uniquely presented with macrocephaly. Tracheo-bronchomalacia has been described once previously but had a significant impact on this patient's clinical course. The patient passed away at 2-month-old due to cardiac and respiratory complications. Chromosomal single nucleotide polymorphism (SNP) microarray analysis on a peripheral blood sample from the patient revealed trisomy 12 in approximately 50% of cells. Concurrent fluorescence in situ hybridization analysis of uncultured blood cells detected a comparable level of trisomy 12 mosaicism. Compared to conventional cytogenetics, SNP microarray examines all nucleated cells without sampling bias, has an increased power to estimate mosaicism level, and can provide a quick assessment of the underlying mechanism. Here we demonstrate the utilization of SNP microarray in the clinical diagnosis of those once considered rare disorders but might have been missed by conventional cytogenetic techniques.

A homozygous variant in growth and differentiation factor 2 (GDF2) may cause lymphatic dysplasia with hydrothorax and nonimmune hydrops fetalis

The etiology of nonimmune hydrops fetalis is extensive and includes genetic disorders. We describe a term-born female neonate with late onset extensive nonimmune hydrops, that is, polyhydramnios, edema, and congenital bilateral chylothorax. This newborn was successfully treated with repetitive thoracocentesis, total parenteral feeding, octreotide intravenously and finally surgical pleurodesis and corticosteroids. A genetic cause seemed plausible as the maternal history revealed a fatal nonimmune hydrops fetalis. A homozygous truncating variant in GDF2 (c.451C>T, p.(Arg151*)) was detected with exome sequencing. Genetic analysis of tissue obtained from the deceased fetal sibling revealed the same homozygous variant. The parents and two healthy siblings were heterozygous for the GDF2 variant. Skin and lung biopsies in the index patient, as well as the revised lung biopsy of the deceased fetal sibling, showed lymphatic dysplasia and lymphangiectasia. To the best of our knowledge, this is the first report of an association between a homozygous variant in GDF2 with lymphatic dysplasia, hydrothorax and nonimmune hydrops fetalis.

Prenatal diagnosis of low-level mosaic trisomy 20 by amniocentesis in a pregnancy with a favorable outcome

OBJECTIVE

We present prenatal diagnosis of low-level mosaic trisomy 20 by amniocentesis in a pregnancy with a favorable outcome.

CASE REPORT

A 35-year-old woman underwent amniocentesis at 17 weeks of gestation because of advanced maternal age. Amniocentesis revealed a karyotype of 47,XX,+20[8]/46,XX[23]. The parental karyotypes were normal, and prenatal ultrasound findings were unremarkable. Repeat amniocentesis performed at 20 weeks of gestation revealed a karyotype of 47,XX,+20[2]/46,XX[19]. Simultaneous molecular cytogenetic tests using uncultured amniocytes revealed no genomic imbalance in array comparative genomic hybridization (aCGH) analysis and a mosaic level of 14.3% (15/105 cells) in interphase fluorescence in situ hybridization (FISH) analysis. Polymorphic DNA marker analysis using the DNAs extracted from uncultured amniocytes and parental bloods excluded uniparental disomy 20. At 39 weeks of gestation, a phenotypically normal 3580-g female baby was delivered without any structural abnormality. The neonate was doing well at age two years during postnatal follow-ups. Her psychomotor development was normal. Interphase FISH analysis of urinary cells revealed no trisomy 20 signals in 45/45 urinary cells. The peripheral blood had a karyotype of 46,XX in 40/40 lymphocytes.

CONCLUSION

Fetuses with low-level mosaic trisomy 20 at amniocentesis can have a favorable outcome. Molecular cytogenetic analysis on uncultured amniocytes is useful for confirmatory diagnosis of the mosaic level in case of mosaic trisomy 20 at amniocentesis with different mosaic levels at different amniocenteses.

Assessing the true incidence of mosaicism in preimplantation embryos

Modern technologies applied to the field of preimplantation genetic diagnosis for aneuploidy screening (PGD-A) have improved the ability to identify the presence of mosaicism. Consequently, new questions can now be addressed regarding the potential impact of embryo mosaicism on diagnosis accuracy and the feasibility of considering mosaic embryos for transfer. The frequency of chromosomal mosaicism in products of conception (POCs) of early miscarriages has been reported to be low. Mosaic embryos with an aneuploid inner cell mass are typically lost during the first trimester owing to spontaneous miscarriages. Most of the mosaics in established pregnancies would derive from placental mosaicism or placental aneuploidy, and mosaic embryos with aneuploid inner cell mass should be lost mainly due to first-trimester spontaneous miscarriages. The well described clinical outcomes of live births from mosaic embryos suggest a wide spectrum of phenotypes, from healthy to severely impaired. Therefore, there is a need to balance the risks of discarding a possibly viable embryo with that of transferring an embryo that may ultimately have a lower implantation potential.

Interphase fluorescence in situ hybridization assisting in prenatal counseling for amniocentesis karyotyping-detected fetal mosaicism

OBJECTIVE

To evaluate how interphase fluorescence in situ hybridization (FISH) played a role in genetic counseling when encountering prenatally detected fetal mosaicism cases.

MATERIALS AND METHODS

We retrospectively reviewed 17 cases of amniotic fluid specimens diagnosed with Level III chromosome mosaicism using in situ coverslip culture method. Among them, seven received additional interphase FISH tests; five were related to autosomal mosaicism and two others were due to sex chromosomes.

RESULTS

In the autosome group, one couple chose to terminate the pregnancy due to a high percentage of trisomy 21 cells (48.1%) shown on interphase FISH; in the gonosome group, one case chose termination as FISH exhibited as high as 80% of XXYY cells.

CONCLUSION

Performing interphase FISH on uncultured amniocytes for cases detected with mosaicism by traditional amniotic fluid culture provided quick confirmation of the karyotyping results; additionally, obtaining information about the extent of the abnormality involved using interphase FISH could also play a role in counseling patients on the decision making concerning the future of their pregnancies.

Maternal uniparental disomy of chromosome 20: a novel imprinting disorder of growth failure

PURPOSE

Maternal uniparental disomy of chromosome 20 (UPD(20)mat) has been reported in only four patients, three of whom also had mosaicism for complete or partial trisomy of chromosome 20. We sought to evaluate the clinical significance of isolated UPD(20)mat in eight individuals.

METHODS

We evaluated phenotypic and genomic findings of a series of eight new patients with UPD(20)mat.

RESULTS

All eight individuals with UPD(20)mat had intrauterine growth restriction, short stature, and prominent feeding difficulties with failure to thrive. As a common feature, they often required gastric tube feeds. Genomic data in most patients are indicative of UPD as a result of trisomy rescue after meiosis II nondisjunction.

CONCLUSION

We describe the first natural history of the disorder and the results of therapeutic interventions, including the frequent requirement of direct gastric feedings only during the first few years of life, and propose that growth hormone supplementation is probably safe and effective for this condition. We suggest that UPD(20)mat can be regarded as a new imprinting disorder and its identification requires specialized molecular testing, which should be performed in patients with early-onset idiopathic isolated growth failure.Genet Med 18 4, 309-315.

Dissecting the phenotype of supernumerary marker chromosome 20 in a patient with syndromic Pierre Robin sequence: combinatorial effect of gene dosage and uniparental disomy

Clinical phenotypes in individuals with a supernumerary marker chromosome (SMC) are mainly caused by gene dosage effects due to the genes located on the SMC. An additional effect may result from uniparental disomy (UPD). Consequently, the occurrence of UPD may be a confounding factor in identifying genotype-phenotype correlations in SMC syndromes. Here, we report on a patient that illustrates this problem; the phenotype of this patient was a consequence of a combined effect of gene dosage and UPD. The proband showed facial dysmorphisms, growth retardation and developmental delay. G-band karyotype of the proband's peripheral blood showed the presence of mosaic SMC. A SNP array analysis documented maternal UPD20 and 20p duplication. It is known that maternal UPD20 causes prenatal onset growth retardation and feeding difficulties. By contrast, duplication of 20p causes facial dysmorphisms, micrognathia, cleft palate, developmental delay and vertebral anomalies. Our classification of the proband's phenotype showed a mixture of these two effects. Therefore, we suggest the routine use of genome-wide SNP array towards the detailed genotype-phenotype correlations for SMC syndromes.

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.

Chromosome aberrations identified by cytogenetic analysis of the first two clones of cultured amniotic fluid cells compared with QF-PCR results

We report on our experience of studying amniotic fluid cells by cytogenetic analysis (CA) of the first 2 clones. We investigated the incidence and types of chromosome aberrations detected by CA of 196 amniocenteses performed on pregnant women at high risk. Of these cases, 178 were analysed by QF-PCR (risk group A). The results were compared with the data obtained by CA of 1,263 amniocenteses carried out in patients with other indications. QF-PCR was used to investigate 1,030 of these cases (risk group B). The combined average turnaround time for a CA result of the first 2 clones in both risk groups was within 9 ± 2 days. The final CA results (≥6 clones) were obtained within 12 ± 4 days. In risk group A, CA was not possible in 2 cases due to cell culture failure. The foetal karyotype was abnormal in 13.8% of the cases by CA of ≥6 clones and in 13.5% of the cases by QF-PCR. Together, CA of ≥6 clones and QF-PCR detected chromosome aberrations in 14.8% of the cases. With the exception of 2 cases of in vitro culture failure and 1 case with low gonosomal mosaicism, CA of the first 2 clones detected all cases with chromosome aberrations. Five cases with clinically significant chromosome aberrations were not detected by QF-PCR. In risk group B, the foetal karyotype was found to be abnormal in 2.2% of the cases by CA of ≥6 clones and in 1.0% of the cases by QF-PCR. Together, CA of ≥6 clones and QF-PCR revealed chromosome aberrations in 2.2% of the cases. With the exception of 1 case with low gonosomal mosaicism, CA of the first 2 clones detected all other cases with chromosome aberrations. The majority of these cases were inherited chromosome aberrations. Eighteen cases with chromosome aberrations were not detected by QF-PCR. Based on our results, CA of ≥6 clones, together with QF-PCR as a first test, should be performed in all prenatal cases with abnormal ultrasound findings. In pregnancies with other indications, CA of the first 2 clones alone is sufficient to identify all clinically significant (and inherited) chromosome aberrations.

CCMG guidelines: prenatal and postnatal diagnostic testing for uniparental disomy

The aim of this statement is to provide clinicians, cytogeneticists and molecular geneticists of the Canadian College of Medical Geneticists (CCMG) a comprehensive review of the role of UPD in constitutional genetic diagnosis and to provide a guideline as to when investigation for UPD is recommended. Members of the CCMG Cytogenetics, Molecular Genetics, Clinical Practice, and Prenatal Diagnosis committees reviewed the relevant literature on uniparental disomy (UPD) in constitutional genetic diagnosis (May 2010). Guidelines were developed for UPD testing in Canada. The guidelines were circulated for comment to the CCMG members at large and following appropriate modification, approved by the CCMG Board of Directors (July 2010).

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.

Genome-wide detection of uniparental disomy in a fetus with intrauterine growth restriction using genotyping microarrays

OBJECTIVE

To present the clinical and molecular features of a fetus with confined trisomy 16 mosaicism with maternal uniparental disomy (UPD), using various prenatal diagnostic techniques.

MATERIALS AND METHODS

Chromosomal karyotyping was performed on samples of chorionic villi, amniotic fluid cells, amniotic membrane, umbilical cord, fetal skin, and placenta from a fetus with elevated nuchal translucency. Polymorphic short tandem repeat markers and Affymetrix single nucleotide polymorphism (SNP) mapping chips were used for molecular analyses.

RESULTS

Karyotypes from chorionic villi and amniocytes showed 47,XX,+16 and 46,XX, respectively. Short tandem repeat markers on chromosome 16 suggested maternal UPD for chromosome 16. Affymetrix 10K SNP mapping chips were used to simultaneously confirm the difference in karyotypes between the placenta and amniocytes and to diagnose UPD for chromosome 16. Fetal ultrasonography and magnetic resonance imaging identified severe intrauterine growth restriction (IUGR). Autopsy revealed IUGR, incomplete lobulation of bilateral lungs, and malrotation of the intestines. The karyotypes of umbilical cord, fetal skin and amniotic membrane were 46,XX, and the trisomy 16 karyotype appeared to be confined to the placenta.

CONCLUSION

UPD should be investigated as a possible etiology in all cases of unexplained IUGR. SNP microarrays can be useful for confirming this diagnosis.

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.

Pregnancy and postnatal outcome of mosaic isochromosome 20q

Prenatally diagnosed mosaicism for isochromosome 20q is generally reported in association with a normal outcome at birth and is rarely confirmed postnatally. However, the origin of these abnormal cells is unclear and there are few reports of long-term outcomes. We present an additional case of prenatally detected isochromosome 20q, with normal outcome up to age 3.6 years. The abnormal cells, while present at high levels in the amniotic fluid, could not be confirmed in placenta or fetal blood. Nonetheless, based on a review of the literature, the level of isochromosome 20q cells found is associated with risk of abnormal outcome, suggesting a possible effect in some cases.

Cryptic mosaicism for monosomy 20 identified in renal tract cells

We report a post-natal case of mosaic aneuploidy for chromosome 20 in a 4 months old male baby with an abnormal phenotype including dysmorphic features (asymmetric facial growth), ventricular septal defect, hypotonia and bilateral vesicoureteric reflux. Conventional cytogenetics on peripheral blood showed 1 cell of 200 with 47,XY,+20. Further investigations using fluorescent in situ hybridization (FISH) on a urine sample, with a centromere probe for chromosome 20, revealed 39 of 50 cells giving one signal indicative of monosomy 20. FISH analysis of a buccal smear was consistent with disomy 20 as was conventional cytogenetics on skin fibroblasts. This is the fourth reported case of mosaic monosomy 20, the second case where monosomy 20 is present with a trisomy 20 cell and the first case with each aneuploidy found in two separate tissues. The identification of mosaicism is a difficult task since the abnormal cells can be present only in certain tissues and may disappear with selection as the fetus develops, thus leading to single-cell abnormalities that may get dismissed (pseudomosaicism). The use of FISH in this case was crucial in identifying the cryptic mosaic monosomy 20 cell line. The likely mechanism of origin is post-zygotic nondisjunction giving rise to monosomy, disomy and trisomy cell(s) in the same or different tissues. Although no other trisomy 20 cells were found, the abnormal phenotype plus the finding of a monosomy 20 cell line make this mechanism the most plausible explanation. Had we dismissed the single-cell abnormality, the cryptic mosaicism of monosomy 20 would not have been identified. A detailed analysis of all tissues accessible in conjunction with careful consideration of all clinical information available is the best course of action in suspected mosaicism.

Amniotic trisomy 11 mosaicism—is it a benign finding?

OBJECTIVES

A case of prenatally diagnosed trisomy 11 mosaicism with a normal outcome is reported and the medical literature on prenatal detection of this finding is reviewed.

METHODS

Proportion of cells with trisomy 11 was evaluated in amniocytes, fetal blood lymphocytes, newborn fibroblasts and urinary epithelial cells. Karyotype studies and fluorescence in situ hybridization analysis using the 11q13LS1 CCND1 probe were performed.

RESULTS

Trisomy 11 level III mosaicism of 26% was detected in amniotic fluid cells. Periumbilical blood sampling showed a normal fetal karyotype. No fetal structural abnormalities were noted on ultrasound scan. The infant was spontaneously delivered and had normal physical findings at birth. No evidence of trisomic cells was found on extensive postnatal evaluation, implying an extraembryonic origin. Molecular analysis excluded uniparental disomy of chromosome 11. At 1 year of age, the baby is developing normally.

CONCLUSIONS

Only three reports on trisomy 11 mosaicism identified at amniocentesis have been published previously, all with a normal outcome. Additional cases of prenatally diagnosed mosaicism for trisomy 11 are necessary to assess more accurately the clinical significance of this finding.