Molecular cytogenetics in prenatal diagnosis

Prenatal diagnosis (PD) startcd in the fifties when variotls groups indicated the possibility of prenatal sex determination in amniotic fluid (AF) cells (SeIT et al., 1955; Fuchs and Riis, 1956; Dewhurst, 1956). After the first succesful attempts at AF cell cultivation and karyotyping by SteeIe and Breg (1966) and T1tiede et al. (1966), the first small series of prcnatal chromosomc analyses were presented (Jacobsoll aud Barter, 1967), aud the ficst chromosome aberrations in cultured AF cells were detected (Valenti et al., 1969). AF cells could also be used for prenatal detcction of inham errors of metabolism (NadIer, 1968). Our eentre made an important international contribution towards experienee with a large number of biochemical assays, and the devclopment of ultramicrochemical techlliques penllitting a rapid PD (Galjaard, 1972; Niermeijer, 1975; Galjaard, 1976a, 1979, 1980; Galjaard et al., 1977; K1eijer, 1990). AtlOther important contribution to PD was the finding by Broek and Sutcliffe (1972), that the alpha-fetoprotein level in AF is increascd when the fetus has an open neural tube defect

Patient-friendly integrated first trimester screening by NIPT and fetal anomaly scan

Many major structural fetal anomalies can be diagnosed by first trimester fetal anomaly scan. NIPT can accurately detect aneuploidies and large chromosomal aberrations in cfDNA in maternal blood plasma. This study shows how a patient-friendly first trimester screening for both chromosomal and structural fetal anomalies in only two outpatient visits can be provided. Genotype-first approach assures not only the earliest diagnosis of trisomy 21 (the most prevalent chromosome aberration), but also completion of the screening at 12–14 weeks. To ensure proper management and avoid unnecessary anxiety abnormal NIPT different from trisomy 21, 18 and 13 should be referred for genetic counseling

Multiplex ligation dependent probe amplification (MLPA) for rapid distinction between unique sequence positive and negative marker chromosomes in prenatal diagnosis

Background: Small supernumerary marker chromosomes (sSMC) are extra structurally abnormal chromosomes that cannot be unambiguously identified with conventional chromosome banding techniques. These marker chromosomes may cause an abnormal phenotype or be harmless depending on different factors such as genetic content, chromosomal origin and level of mosaicism. When a sSMC is found during prenatal diagnosis, the main question is whether the sSMC contains euchromatin since in most cases this will lead to phenotypic abnormalities. We present the use of Multiplex Ligation Dependent probe Amplification (MLPA) for rapid distinction between non-euchromatic and euchromatic sSMC. Results: 29 well-defined sSMC found during prenatal diagnosis were retrospectively investigated with MLPA with the SALSA MLPA centromere kits P181 and P182 as well as with the SALSA MLPA telomere kits P036B and P070 (MRC Holland BV, Amsterdam, The Netherlands). All unique-sequence positive sSMC were correctly identified with MLPA, whereas the unique-sequence negative sSMC had normal MLPA results. Conclusions: Although different techniques exist for identification of sSMC, we show that MLPA is a valuable adjunctive tool for rapidly distinguishing between unique-sequence positive and negative sSMC. In case of positive MLPA results, genetic microarray analysis or, if not available, targeted FISH can be applied for further identification and determination of the exact breakpoints, which is important for prediction of the fetal phenotype. In case of a negative MLPA result, which means that the sSMC most probably does not contain genes, the parents can already be reassured and parental karyotyping can be initiated to assess the heritability. In the mean time, FISH techniques are needed for determination of the chromosomal origin

Retrospective study of trisomy 18 in chorionic villi with fluorescent in situ hybridization on archival direct preparations

Trisomy 18 in direct chorionic villus preparations needs further investigation since the chromosome abnormality may be confined to the placenta and may not represent the actual fetal karyotype. We performed, retrospectively, fluorescent in situ hybridization (FISH) with the chromosome 18 centromere probe (L1.84) on interphase nuclei of destained slides of all cases of full trisomy 18 (n=22) and mosaic trisomy 18 (n=8) detected among 7600 first-trimester chorionic villus samples during an 8-year period (1985–1992). More nuclei displaying three signals were encountered in cases of full and mosaic trisomy 18 confirmed in fetal tissue than in non-confirmed cases. FISH can be useful for the verification of trisomy 18 in direct chorionic villus preparations

A chromosome 21-specific cosmid cocktail for the detection of chromosome 21 aberrations in interphase nuclei

Fluorescent in situ hybridization (FISH) with a 21q11-specific probe (CB21c1) consisting of three non-overlapping cosmids has been applied to interphase amniocytes of pregnancies at increased risk for fetal aneuploidy (N = 78) and to interphase lymphocytes, cultured and uncultured, of patients referred for Down syndrome (N = 19 and 28, respectively). In the uncultured amniocytes, six chromosome aberrations were detected: three cases of trisomy 21, a triploidy, a de novo 46,XX,t(21q21q), and a mosaic 46,XY/47,XY,+dic(21)(q11)/48,XY,+dic(21)(q11), +del(21)(q11). In 15 cultured and 20 uncultured blood samples, FISH correctly diagnosed trisomy 21 (full or mosaic) at the interphase level, which was confirmed in all cases by subsequent karyotyping. Because of specific and strong signals in interphase nuclei, CB21c1 appears to be a useful tool for the rapid detection of chromosome 21 abnormalities

Prenatally diagnosed submicroscopic familial aberrations at 18p11.32 without phenotypic effect

Background: Recent development of MLPA (Multiplex-Ligation-dependent Probe Amplification, MRC-Holland) and microarray technology allows detection of a wide range of new submicroscopic abnormalities. Publishing new cases and case reviews associated with both clinical abnormalities and a normal phenotype is of great value. Findings/results. We report on two phenotypically normal foetuses carrying a maternally-inherited interstitial submicroscopic abnormality of chromosome 18p11.32. Both abnormalities were found with the aneuploidy MLPA kit P095 during rapid aneuploidy detection, which was offered along with conventional karyotyping. Foetus 1 and its mother have a 1,7 Mb deletion and foetus 2 and its mother have a 1,9 Mb duplication. In both cases normal babies were born. We used the HumanCytoSNP-12 array of Illumina to visualize the CNVs and map the breakpoints. Conclusions: We suggest that a CNV at 18p11.32 (528,050-2,337,486) may represent a new benign euchromatic variant

Increased incidence of cytogenetic abnormalities in chorionic villus samples from pregnancies established by in vitro fertilization and embryo transfer (IVF-ET)

We studied 201 pregnancies that were established by in vitro fertilization and embryo transfer (IVF–ET) and compared the frequency of cytogenetic abnormalities with that found in a large control population matched for indication group (advanced maternal age) and time of sampling. A total of 252 IVF–ET fetuses were cytogenetically analysed by either chorionic villus sampling (CVS; n = 80) or amniocentesis (n = 172). Eleven chromosome abnormalities were found in the CVS group (13·8 per cent); among them, a 45, X/46, X, dic(q11)/46, X, del(Y)(q11) mosaic that was found in an IVF pregnancy established by intracytoplasmic sperm injection (ICSI), four cases of trisomy 21, and three cases of trisomy 7 confined to the placenta. The results indicate a statistically significant three‐to five‐fold increase in both confined placental abnormalities (P<0·008) and true fetal chromosome anomalies (P<0·04). In the amniocentesis group, identical rates (1·7 per cent) of chromosome abnormalities were found in the IVF–ET and control groups. It is concluded that late first trimester, but not early second trimester, IVF–ET pregnancie

Nuchal translucency of 3.0-3.4 mm an indication for NIPT or microarray? Cohort analysis and literature review

Introduction: Currently fetal nuchal translucency (NT) ≥3.5 mm is an indication for invasive testing often followed by chromosomal microarray. The aim of this study was to assess the risks for chromosomal aberrations in fetuses with an NT 3.0-3.4 mm, to determine whether invasive prenatal testing would be relevant in these cases and to assess the residual risks in fetuses with normal non-invasive prenatal test (NIPT) results. Material and methods: A retrospective study and meta-analysis of literature cases with NT between 3.0 and 3.4 mm and 2 cohorts of pregnant women referred for invasive testing and chromosomal microarray was performed: Rotterdam region (with a risk >1:200 and NT between 3.0 and 3.4 mm) tested in the period July 2012 to June 2019 and Central Denmark region (with a risk >1:300 and NT between 3.0 and 3.4 mm) tested between September 2015 and December 2018. Results: A total of 522 fetuses were referred for invasive testing and chromosomal microarray. Meta-analysis indicated that in 1:7.4 (13.5% [95% CI 8.2%-21.5%]) fetuses a chromosomal aberration was diagnosed. Of these aberrant cases, 47/68 (69%) involved trisomy 21, 18, and 13 and would potentially be detected by all NIPT approaches. The residual risk for missing a (sub)microscopic chromosome aberration depends on the NIPT approach and is highest if NIPT was performed only for common trisomies–1:21 (4.8% [95% CI 3.2%-7.3%]). However, it may be substantially lowered if a genome-wide 10-Mb resolution NIPT test was offered (~1:464). Conclusions: Based on these data, we suggest that the NT cut-off for invasive testing could be 3.0 mm (instead of 3.5 mm) because of the high risk of 1:7.4 for a chromosomal aberration. If women were offered NIPT first, there would be a significant diagnostic delay because all abnormal NIPT results need to be confirmed by diagnostic testing. If the woman had already received a normal NIPT result, the residual risk of 1:21 to 1:464 for chromosome aberrations other than common trisomies, dependent on the NIPT approach, should be raised. If a pregnant woman declines invasive testing, but still wants a test with a broader coverage of clinically significant conditions then the genome-wide >10-Mb resolution NIPT test, which detects most aberrations, could be proposed