A case of discordant related abnormal karyotypes from chorionic villi and amniocytes

A Case Report of a Feto-Placental Mosaicism Involving a Segmental Aneuploidy: A Challenge for Genome Wide Screening by Non-Invasive Prenatal Testing of Cell-Free DNA in Maternal Plasma

Non-invasive prenatal testing (NIPT) using cell-free DNA can detect fetal chromosomal anomalies with high clinical sensitivity and specificity. In approximately 0.1% of clinical cases, the NIPT result and a subsequent diagnostic karyotype are discordant. Here we report a case of a 32-year-old pregnant patient with a 44.1 Mb duplication on the short arm of chromosome 4 detected by NIPT at 12 weeks' gestation. Amniocentesis was carried out at 18 weeks' gestation, followed by conventional and molecular cytogenetic analysis on cells from the amniotic fluid. SNP array analysis found a de novo deletion of 1.2 Mb at chromosome 4, and this deletion was found to be near the critical region of the Wolf-Hirschhorn syndrome. A normal 46,XY karyotype was identified by G-banding analysis. The patient underwent an elective termination and molecular investigations on tissues from the fetus, and the placenta confirmed the presence of type VI true fetal mosaicism. It is important that a patient receives counselling following a high-risk call on NIPT, with appropriate diagnostic analysis advised before any decisions regarding the pregnancy are taken. This case highlights the importance of genetic counselling following a high-risk call on NIPT, especially in light of the increasing capabilities of NIPT detection of sub-chromosomal deletions and duplications.

Chromosomal Mosaicism in Human Feto-Placental Development: Implications for Prenatal Diagnosis

Chromosomal mosaicism is one of the primary interpretative issues in prenatal diagnosis. In this review, the mechanisms underlying feto-placental chromosomal mosaicism are presented. Based on the substantial retrospective diagnostic experience with chorionic villi samples (CVS) of a prenatal diagnosis laboratory the following items are discussed: (i) The frequency of the different types of mosaicism (confined placental, CPM, and true fetal mosaicisms, TFM); (ii) The risk of fetal confirmation after the detection of a mosaic in CVS stratified by chromosome abnormality and placental tissue involvement; (iii) The frequency of uniparental disomy for imprinted chromosomes associated with CPM; (iv) The incidence of false-positive and false-negative results in CVS samples analyzed by only (semi-)direct preparation or long term culture; and (v) The implications of the presence of a feto-placental mosaicism for microarray analysis of CVS and non-invasive prenatal screening (NIPS).

SNP array and phenotype correlation shows that FLI1 deletion per se is not responsible for thrombocytopenia development in Jacobsen syndrome

Jacobsen syndrome (JBS) is a rare chromosomal disorder caused by terminal deletion of the long arm of chromosome 11. We report on four prenatally diagnosed patients with JBS with variable prenatal and postnatal phenotypes and 11q deletions of varying sizes. Precise characterization of the deleted region in three patients was performed by SNP arrays. The severity of both the prenatal and postnatal phenotypes did not correlate with the size of the haploinsufficient region. Despite the large difference in the deletion size (nearly 6 Mb), both of the live-born patients had similar phenotypes corresponding to JBS. However, one of the most prominent features of JBS, thrombocytopenia, was only present in the live-born boy. The girl, who had a significantly longer deletion spanning all four genes suspected of being causative of JBS-related thrombocytopenia (FLI1, ETS1, NFRKB, and JAM3), did not manifest a platelet phenotype. Therefore, our findings do not support the traditional view of deletion size correlation in JBS or the causative role of FLI1, ETS1, NFRKB, and JAM3 deletion per se for the development of disease-related thrombocytopenia.

Prenatal diagnosis of mosaicism for 11q terminal deletion

The phenotype of 11q terminal deletion also known as Jacobsen syndrome is a clinically well known entity whose diagnosis in infancy and childhood is based on clinical examination, hematological and cytogenetic findings. Hematological features in Jacobsen syndrome are very similar to those reported in Paris-Trousseau syndrome (PTS) which is also associated with11q terminal deletion. Karyotype analysis shows a variable terminal deletion from 11q23 sub-band extending to the telomere. Most often in patients with Jacobsen syndrome, this chromosomal deletion is present in all metaphases. We report on the identification of a distal 11q deletion in mosaic (20% of deleted cells) in a fetus ascertained after amniocentesis for maternal serum screening test indicative for Down syndrome. The present case is the third prenatal diagnosis of a mosaic for a distal 11q deletion with the lowest mosaicism rate. The 2D-ultrasound examination and cord blood hematological studies were useful to estimate the prognosis at term, considering the contribution of the mosaicism rate to the phenotypic variability in Jacobsen syndrome. The identification of mosaicism for distal 11q deletion is a very rare event in prenatal diagnosis. This case illustrates the complexity in genetic counselling for prenatally ascertained partial monosomy 11qter in mosaic.

(Potential) false-negative diagnoses in chorionic villi and a review of the literature

OBJECTIVES

To assess the incidence of (potential) false-negative findings of cytogenetic diagnosis in STC-villi and/or LTC-villi and to determine the best strategy for karyotyping chorionic villi in order to avoid false-negative results.

METHODS

2476 chorionic villus samples were received for prenatal cytogenetic investigations. Karyotyping was routinely performed on STC- and LTC-villi preparations by G-banding. Fluorescence in situ hybridization (FISH) analyses were performed in addition to standard chromosome analysis when necessary. Sometimes follow-up investigations like amniocentesis were performed before a definite prenatal cytogenetic result could be reported.

RESULTS

In 2389/2476 (96.5%) of the cases, both STC- and LTC-villi were investigated. Normal STC- with abnormal LTC-villi results and finally an abnormal fetal karyotype were detected in ten cases (10/2389; 0.42%); in 9/10 of the cases the indication was fetal ultrasound abnormalities. Normal STC- and LTC-villi and finally an abnormal fetal karyotype were detected in two cases (2/2389; 0.08%).

CONCLUSION

The most reliable technique for prenatal diagnosis after chorionic villus sampling (CVS) is the combination of the analysis of both STC- and LTC-villi to reduce the incidence of false-negative findings to a minimum. In the case of fetal ultrasound abnormalities with a small amount of villi available, the investigation of LTC-villi is recommended over that of STC-villi.

Prenatal diagnosis ofde novo proximal interstitial deletion of 9q and review of the literature of uncommon aneuploidies associated with increased nuchal translucency

OBJECTIVES

To present the prenatal diagnosis and molecular cytogenetic analysis of de novo proximal interstitial deletion of 9q and to review the literature of uncommon aneuploidies associated with increased nuchal translucency (NT).

CASE

Obstetric ultrasound at 11 weeks' gestation revealed an increased NT thickness of 6.6 mm in a 31-year-old primigravid woman. At 13 weeks' gestation, repeat ultrasound examinations revealed a normal NT thickness of 1.8 mm. The subcutaneous nuchal fluid accumulation was no longer present at the following ultrasound scans. An amniocentesis was performed at 18 weeks' gestation.

RESULTS

Cytogenetic analysis revealed a karyotype of 46,XX,del(9)(q21.1q22.2). The parental karyotypes were normal. At 21 weeks' gestation, a 442-g female fetus was delivered with low-set ears, hypertelorism, and a thick nuchal fold. The parental origin of the interstitial deletion of 9q was analyzed with polymorphic DNA markers. With the microsatellite markers D9S238 (9q13), D9S889 (9q21.11), and D9S253 (9q22.2), two alleles inherited from the parents were seen in the proband, but with markers D9S1780 (9q21.31), D9S303 (9q21.32), D9S252 (9q21.33), and D9S316 (9q22.1), only one maternal allele was present. The deletion was of paternal origin.

CONCLUSIONS

Fetuses with uncommon aneuploidies may manifest increased NT in the first trimester. The present case provides evidence for a correlation between increased NT and interstitial 9q deletion. Prenatal identification of increased NT should alert subtle structural chromosome aberrations and prompt high-resolution karyotyping.

Prenatal diagnosis of trisomy 21 by i(21q): a rare case of fetoplacental chromosomal discrepancy

OBJECTIVE

A study was conducted to explain the mechanism of an unusual discrepancy between short- and long-term culture examination methods of chorionic villus sampling (CVS).

METHOD

In a 29-year-old Caucasian woman, transabdominal CVS was carried out at 12 weeks of gestation. Non-mosaic karyotype 46,XX,i(21q) was found on long-term CVS culture but number and morphology of chromosomes were normal on short-term culture, amniocyte culture, hygroma colli fluid and fetal fibroblast.

RESULTS

Chromosomal aberration probably appeared after the trophoblast cell line differentiation, four days after fertilization, by means of a 21 centromere misdivision and formation of a i(21q) with secondary positive selection of the 46,XX,i(21q) cell line and loss of the 46,XX in the fetus.

CONCLUSION

The restricted number of cases with this type of discrepancy limits the possibility of drawing generalised conclusions. In case of discrepancy, we recommend confirmation by amniocentesis or by fetal blood combined with sonographic examination to provide a more definitive diagnosis.

Prenatal diagnosis of de novo distal 11q deletion associated with sonographic findings of unilateral duplex renal system, pyelectasis and orofacial clefts

In utero diagnosis of de novo distal 11q deletion associated with renal and orofacial malformations has not been previously described. We present a 35-year-old pregnant woman with prenatal sonographic findings of a unilateral duplex renal system, pyelectasis and orofacial clefts at 20 weeks' gestation. Both genetic amniocentesis and postnatal cytogenetic analysis revealed de novo 46,XX,del(11)(q23). After birth, the fetus manifested a dysmorphic phenotype correlated with del(11q) syndrome. Genetic marker analysis showed a paternally derived distal deletion of chromosome 11q and a breakpoint centromeric to D11S1341. The present case represents the earliest prenatal diagnosis of a duplex renal system, pyelectasis and an additional feature of orofacial clefts associated with distal 11q deletion. Prenatal sonographic detection of a duplex renal system, pyelectasis and orofacial clefts should warrant a careful assessment of fetal anatomy and prompt cytogenetic analysis looking for chromosomal aberrations.