Prenatal diagnosis of mosaic trisomy 2 associated with abnormal maternal serum screening, oligohydramnios, intrauterine growth restriction, ventricular septal defect, preaxial polydactyly, and facial dysmorphism

Low-level mosaic trisomy 2 at amniocentesis in a pregnancy associated with positive NIPT and CVS results for trisomy 2, maternal uniparental disomy 2, perinatal progressive decrease of the aneuploid cell line, cytogenetic discrepancy between cultured amniocytes and uncultured amniocytes, intrauterine growth restriction and a favorable fetal outcome

OBJECTIVE

We present low-level mosaic trisomy 2 at amniocentesis in a pregnancy associated with positive non-invasive prenatal testing (NIPT) and chorionic villus sampling (CVS) results for trisomy 2, maternal uniparental disomy (UPD) 2, perinatal progressive decrease of the aneuploid cell line, cytogenetic discrepancy between cultured amniocytes and uncultured amniocytes, intrauterine growth restriction (IUGR) and a favorable fetal outcome.

CASE REPORT

A 35-year-old, primigravid woman underwent amniocentesis at 16 weeks of gestation because both NIPT at 9 weeks of gestation and CVS at 11 weeks of gestation revealed trisomy 2. This pregnancy was conceived by in vitro fertilization (IVF) and embryo transfer (ET). Amniocentesis revealed a karyotype of 47,XY,+2[11]/46,XY[19]. Prenatal ultrasound findings were normal. She was referred to the hospital for genetic counseling at 20 weeks of gestation, and repeat amniocentesis performed at 24 weeks of gestation revealed a karyotype of 46,XY (22/22 colonies). The parental karyotypes were normal. Quantitative fluorescent polymerase chain reaction (QF-PCR) analysis on the DNA extracted from uncultured amniocytes and parental bloods revealed maternal uniparental heterodisomy of chromosome 2. Simultaneous molecular cytogenetic analysis on uncultured amniocytes showed the results of arr 2p25.3q37.3 × 2.4 with a log₂ ratio = 0.26, consistent with 40% mosaicism for trisomy 2 by array comparative genomic hybridization (aCGH), and 28% (28/100 cells) mosaicism for trisomy 2 by interphase fluorescence in situ hybridization (FISH). Despite IUGR on fetal ultrasound, the woman was advised to continue the pregnancy, and a 2252-g phenotypically normal male baby was delivered at 38 weeks of gestation. The karyotypes of cord blood, umbilical cord and placenta were 46,XY (40/40 colonies), 46,XY (40/40 colonies) and 47,XY,+2[9]/46,XY[31], respectively. QF-PCR analysis on cord blood, umbilical cord and placenta confirmed uniparental heterodisomy of chromosome 2 in the cord blood and umbilical cord, and maternal origin of trisomy 2 in the placenta. FISH analysis on buccal mucosal cells at age 1.5 months revealed 8.7% (9/104 cells) mosaicism for trisomy 2. When follow-up at age four months, the neonate manifested a normal phenotype except intermittent hypoventilation. Molecular analysis of the PHOX2B gene revealed a normal result. When follow-up at age one year, he manifested normal development.

CONCLUSION

Mosaic trisomy 2 at prenatal diagnosis should alert the possibility of UPD 2 and include a UPD 2 testing. Low-level mosaic trisomy 2 at amniocentesis can be associated with perinatal progressive decrease of the aneuploid cell line and a favorable fetal outcome.

Prenatal Detection of Trisomy 2: Considerations for Genetic Counseling and Testing

We report on the case of prenatal detection of trisomy 2 in placental biopsy and further algorithm of genetic counseling and testing. A 29-year-old woman with first-trimester biochemical markers refused chorionic villus sampling and preferred targeted non-invasive prenatal testing (NIPT), which showed low risk for aneuploidies 13, 18, 21, and X. A series of ultrasound examinations revealed increased chorion thickness at 13/14 weeks of gestation and fetal growth retardation, a hyperechoic bowel, challenging visualization of the kidneys, dolichocephaly, ventriculomegaly, increase in placental thickness, and pronounced oligohydramnios at 16/17 weeks of gestation. The patient was referred to our center for an invasive prenatal diagnosis. The patient's blood and placenta were sampled for whole-genome sequencing-based NIPT and array comparative genomic hybridization (aCGH), respectively. Both investigations revealed trisomy 2. Further prenatal genetic testing in order to confirm trisomy 2 in amniocytes and/or fetal blood was highly questionable because oligohydramnios and fetal growth retardation made amniocentesis and cordocentesis technically unfeasible. The patient opted to terminate the pregnancy. Pathological examination of the fetus revealed internal hydrocephalus, atrophy of brain structure, and craniofacial dysmorphism. Conventional cytogenetic analysis and fluorescence in situ hybridization revealed chromosome 2 mosaicism with a prevalence of trisomic clone in the placenta (83.2% vs. 16.8%) and a low frequency of trisomy 2, which did not exceed 0.6% in fetal tissues, advocating for low-level true fetal mosaicism. To conclude, in pregnancies at risk of fetal chromosomal abnormalities that refuse invasive prenatal diagnosis, whole-genome sequencing-based NIPT, but not targeted NIPT, should be considered. In prenatal cases of trisomy 2, true mosaicism should be distinguished from placental-confined mosaicism using cytogenetic analysis of amniotic fluid cells or fetal blood cells. However, if material sampling is impossible due to oligohydramnios and/or fetal growth retardation, further decisions should be based on a series of high-resolution fetal ultrasound examinations. Genetic counseling for the risk of uniparental disomy in a fetus is also required.

Identifying biomarkers for prenatal diagnosis of neural tube defects based on "omics"

Neural tube defects (NTDs) are the most severe birth defects and the main cause of newborn death; posing a great challenge to the affected children, families, and societies. Presently, the clinical diagnosis of NTDs mainly relies on ultrasound images combined with certain indices, such as alpha-fetoprotein levels in the maternal serum and amniotic fluid. Recently, the discovery of additional biomarkers in maternal tissue has presented new possibilities for prenatal diagnosis. Over the past 20 years, "omics" techniques have provided the premise for the study of biomarkers. This review summarizes recent advances in candidate biomarkers for the prenatal diagnosis of fetal NTDs based on omics techniques using maternal biological specimens of different origins, including amniotic fluid, blood, and urine, which may provide a foundation for the early prenatal diagnosis of NTDs.

A placental trisomy 2 detected by NIPT evolved in a fetal small Supernumerary Marker Chromosome (sSMC)

BACKGROUND

Non-invasive prenatal testing (NIPT) is a rapidly developing and widely used method in the prenatal screening. Recently, the widespread use of the NIPT caused a neglecting of the limitations of this technology.

CASE PRESENTATION

The 38-year-old woman underwent amniocentesis because of a high risk of trisomy 2 revealed by the genome-wide Non-Invasive Prenatal Test (NIPT). The invasive prenatal diagnosis revealed the mosaicism for a small supernumerary marker chromosome sSMC derived from chromosome 2. Interphase fluorescence in situ hybridization (FISH) on uncultured amniocytes revealed three signals of centromere 2 in 30% of the cells. GTG-banded metaphases revealed abnormal karyotype (47,XX,+mar[21]/46,XX[19]) and was confirmed by array comparative genomic hybridization (aCGH). Cytogenetic analyses (FISH, aCGH, karyotype) on fetal skin biopsies were performed and confirmed the genomic gain of the centromeric region of chromosome 2. In the placenta, three cell lines were detected: a normal cell line, a cell line with trisomy 2 and a third one with only the sSMC.

CONCLUSION

Whole-genome Non-Invasive Prenatal Testing allows not only the identification of common fetal trisomies but also diagnosis of rare chromosomal abnormalities. Especially in such cases, it is extremely important to perform not only NIPT verification on a sample of material other than trophoblast, but also to apply appropriate research methods. Such conduct allows detailed analysis of the detected aberration, thus appropriate clinical validity.

Prenatal diagnosis of mosaic trisomy 2 and literature review

Background

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

Results

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

Conclusions

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

Phenotype to genotype characterization by array-comparative genomic hydridization (a-CGH) in case of fetal malformations: A systematic review

The aim of the current review is to report a-CGH abnormalities identified in fetuses with prenatally diagnosed fetal malformations in whom a normal karyotype was diagnosed with conventional cytogenetic analysis. A systematic electronic search of databases (PubMed/Medline, EMBASE/SCOPUS) has been conducted from inception to May, 2017. Bibliographic analysis has been performed according to PRISMA statement for review. The following keywords were used: 'array-CGH' and 'fetal malformations" and "prenatal diagnosis"; alternatively, "microarray", "oligonucleotide array", "molecular biology", "antenatal diagnostics", "fetal diagnostics", "congenital malformations" and "ultrasound" were used to capture both "a-CGH" and "prenatal". One-hundred and twelve fetuses with prenatally diagnosed fetal malformations with normal karyotyping and a-CGH abnormalities detected are described. Single or multiple microarray abnormalities diagnosed have been classified in relation to different organ/system affected. The most frequent a-CGH abnormalities were detected in cases of congenital heart diseases (CDHs), multiple malformations and central nervous system (CNS) malformations. Maternal or paternal carrier-state was seen in 19.64% (22/112), of cases while the number of reported de novo mutations accounted for 46.42% (52/112) of all CNVs microarray abnormalities. Array-comparative genomic hydridization (a-CGH) may become an integral and complemantary genetic testing when fetal malformations are detected prenatally in fetuses with normal cytogenetic karyotype. In addition, a-CGH enables the identification of CNVs and VOUS and improves the calculation of recurrent risk and the genetic counseling.