To investigate the incidence and clinical significance of chromosomal mosaicism (CM) in prenatal diagnosis by G-banding karyotyping and chromosomal microarray analysis (CMA). This is a single-centre retrospective study of invasive prenatal diagnosis for CM. From 5758 karyotyping results and 6066 CMA results, 104 foetal cases with CM were selected and analysed further. In total, 50% (52/104) of foetal cases with CM were affected by ultrasound-detectable phenotypes. Regardless of whether they were singleton or twin pregnancies, isolated structural defects in one system (51.35%, 19/37 in singletons; 86.67%, 13/15 in twins) and a single soft marker (18.92%, 7/37 in singletons; 13.33%, 2/15 in twins) were the most common ultrasound anomalies. Mosaic autosomal trisomy (19.23%, 20/104) was the most frequent type, and its rate was higher in phenotypic foetuses (28.85%, 15/52) than in non-phenotypic foetuses (9.62%, 5/52). There was no difference in mosaic fractions between phenotypic and non-phenotypic foetuses based on specimen sources or overall classification. Discordant mosaic results were observed in 16 cases (15.38%, 16/104) from different specimens or different testing methods. Genetic counselling and clinical management regarding CM in prenatal diagnosis remain challenging due to the variable phenotypes and unclear significance. Greater caution should be used in prenatal counselling, and more comprehensive assays involving serial ultrasound examinations, different specimens or testing methods verifications and follow-up should be applied.

Chromosomal mosaicism detected by karyotyping and chromosomal microarray analysis in prenatal diagnosis.

Following an ultrasound examination indicating an elevated risk of a fetal chromosomal abnormality, pregnant women are offered prenatal genetic testing to more accurately identify the anomalies' etiology and fetal prognosis. Follow-up genetic testing usually includes G-band karyotyping and/or chromosomal microarray analysis (CMA). These techniques involve an invasive diagnostic procedure such as chorionic villus sampling or amniocentesis, although such procedures are not acceptable for a considerable number of pregnant women because of the procedure-related risk of miscarriage. Noninvasive prenatal testing (NIPT) of cell-free DNA (cfDNA) frommaternal plasma is a potential alternative; this requires only a maternal blood sample to perform. Trisomies 13, 18, and 21 have been detected by NIPT with a high degree of sensitivity and specificity. Detection of subchromosomal copy-number variants using NIPT is also plausible. The aims of this retrospective study were to evaluate the efficacy of NIPT as an alternative to invasive prenatal testing for the detection of fetal genetic aberrations following abnormal ultrasound findings. The study included pregnancies found to be at risk of fetal chromosomal abnormality based on sonographic testing, in which NIPTwas used as a follow-up genetic test. Medical records were reviewed for relevant data including maternal age, initial sonographic findings, results of NIPT, results of any diagnostic genetic testing, and pregnancy outcome. Health, Inc. All rights reserved.

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Clinical Utility of Noninvasive Prenatal Testing in Pregnancies With Ultrasound Anomalies

Smith-Magenis syndrome (SMS, OMIM: 182290) is a multiple congenital anomalies and intellectual disability syndrome due to a 3.45 Mb microdeletion involving 17p11.2 and is estimated to occur about one in 25,000 births. Up to now, the ultrasound findings of the foetus with SMS and their external genital defects in patients are rarely reported. This case indicates that foetus with SMS may presentpolyhydramnios and ventriculomegaly in the second trimester. The newborn male patient had an abnormal phenotype in which he has micropenis and his anus is close to the perineal body. The identification of this case may further expand the phenotypic spectrum of this genetic disorder.

Prenatal diagnosis and neonatal phenotype of a de novo microdeletion of 17p11.2p12 associated with Smith-Magenis syndrome and external genital defects

41 pregnancies in which mosaicism had been found on amniotic fluid culture (AFC) were investigated by fetal blood and repeat AFC karyotyping. Results of both investigations, and the infants, were normal in 15 of 16 cases of autosomal trisomy (including trisomies 8, 9, 13, 18, and 21) and in the 8 cases of sex chromosome mosaicism. In 1 case of trisomy 20 mosaicism the fetal blood karyotype and the infant were normal but the repeat AFC showed mosaicism. Abnormality was confirmed in 5 of 11 cases of mosaicism for structural chromosomal rearrangements and in 4 of 6 cases with de-novo supernumerary marker mosaicism. These findings indicate the potential danger of terminating pregnancies because of trisomic mosaicism in AFC, and the importance of identifying the clinical significance of certain chromosome rearrangements which, even in mosaic form, might lead to severe mental and developmental handicap.

Fetal Blood Sampling in Investigation of Chromosome Mosaicism in Amniotic Fluid Cell Culture

Abstract G-banded karyotyping is the most common approach for the detection of genomic alterations. However, this is unable to detect genomic changes of less than 5 Mb. The ability of fluorescence in situ hybridization (FISH) to detect cryptic chromosomal rearrangements exceeds the resolution of routine karyotype. However, conventional FISH is for targeted regions only, whereas the chromosomal microarray is a whole-genome copy number evaluation technique with a resolution of 10 to 20 kb. In this article, we discuss the application of chromosomal microarray 750 K to 384 consecutive prenatal diagnosis cases. Overall diagnostic yield is 15.36%, and chromosomal microarray accounts for a 3.6% additional detection rate. We suggest applying this technique in routine prenatal diagnosis as a first-tier test in prenatal diagnosis along with a backup culture in all cases. 

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Practical Applications of Chromosomal Microarray in Prenatal Diagnosis

Cordocentesis in our practice is most commonly indicated for rapid karyotyping in the second or third trimester and is regarded as the gold standard for foetal chromosomal aberration diagnosis in pregnancies at high risk for chromosomal abnormalities. In this study, we investigated 3387 umbilical cord blood samples for karyotyping from pregnant women who underwent cordocentesis and explored the pregnancy outcomes of foetal sex chromosome mosaicism and chromosomal polymorphism. Out of the 3387 samples, 182 abnormal karyotypes were detected. Ultrasound soft markers were the most common prenatal diagnostic indication, but the detection rate of abnormal karyotypes was 2.02%, while it was 46.97% in the genome-wide NIPT-positive group. The rate of aneuploidy was lower in the soft marker group than in the other groups. Out of 16 cases with sex chromosome mosaicism, three pregnant women with foetuses with a lower proportion of sex chromosome mosaicism delivered healthy foetuses; the foetus with karyotype 46,X,i(Y)(q10)[20]/45,X[6] showed unclear genitals. Three foetuses with chromosomal polymorphisms had postnatal disorders. NIPT should not be recommended as the first-tier screening for chromosomal aberration for pregnancies with ultrasound soft markers or pathological ultrasound findings, but NIPT can be considered an acceptable alternative for pregnancies with contraindications to cordocentesis or the fear of procedure-related foetal loss. Mosaicism found in amniotic fluid cell culture requires further cordocentesis for karyotype confirmation, and the continuation of pregnancy is safe when a normal karyotype is identified in foetal blood culture. Further genetic testing and parental karyotype analysis are needed for foetal chromosomal polymorphisms.

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Cytogenetic analysis of 3387 umbilical cord blood in pregnant women at high risk for chromosomal abnormalities.

Dandy-Walker malformation (DWM) is characterized by complete or partial agenesis of the cerebellar vermis, cyatic dilatation of the forth ventricle, and enlarged posterior fossa. However, the mechanism is still not completely understood up to now. In this study, we reported a rare case that a foetus with DWM showed partial trisomy 12p and distal 15q deletion. Karyotype analysis and chromosomal microarray analysis (CMA) were not always concordant with each other, and it is suggested that they should be performed for prenatal genetic diagnosis together. DWM is a rare central nervous system malformation, reported in 1/25-30,000 live births, characterized by complete or partial agenesis of the cerebellar vermis, cyatic dilatation of the forth ventricle, and enlarged posterior fossa (Kumar et al. 2001; Klein et al. 2003; Agrawal et al. 2016). The neurological development of children with DWM may range from normal to severely retarded, and cause variable clinical feature. Although several efforts have been made to explore its pathogenesis, however, it is still not completely understood. During the past decade, some genetic loci, microdeletion or duplication have been reported to be associated with DWM, such as 9p trisomy, partial deletions of the long arm of chromosome 13, genes ZIC1 and ZIC4 (von Kaisenberg et al. 2000; McCormack et al. 2003; Grinberg et al. 2004). In the present study, we describe a prenatal diagnosis case that a foetus with DWM on ultrasound scanning accepted genetic testing, and it revealed a microduplication of 12p13.33p11.1 and microdeletion of 15q11.2 in 750K single nucleotide polymorphism (SNP) array, while it showed 46,XX,der(8)(8pter→8q24::12p10→12qter),i(12)(p10) in karyotyping.

Ning Zhang

Papers

Cytogenetic analysis of 3387 umbilical cord blood in pregnant women at high risk for chromosomal abnormalities.

Prenatal diagnosis of the Dandy-Walker malformation associated with partial trisomy 12p and distal 15q deletion.