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Objective: To compare mosaicisms in prenatal chorionic villus samples (CVSs) with corresponding postpartum placental samples., Method: We collected placentas from 15 consecutive cases of mosaicism detected in CVSs and obtained five standardized samples on each placenta after delivery. All pre- and postnatal placental samples were uncultured and analyzed by high-resolution chromosomal microarray., Results: Ten cases of mosaicism for whole chromosome aneuploidy (mWC) and five cases with mosaicism for (sub)chromosomal copy number variations (mCNVs) were included. In 5/10 mWC cases and in 4/5 mCNV cases the prenatally detected aberration was confirmed in the postpartum placenta. Three postpartum placentas revealed various complex aberrations differing from the prenatal results: (1) mosaicisms for different deletions/duplications on 9p and 9q in all samples (prenatal: mosaic 5.3 Mb duplication on 9p24), (2) different regions with deletions/duplications/loss of heterozygosity on 1p in all samples (prenatal: mosaic 2.3 Mb 1p36 duplication), and (3) mosaicism for a duplication on 5q and a deletion on 6p in one out of five samples (prenatal: mosaic trisomy 7)., Conclusion: CNVs constitute a complex subgroup in placental mosaicism. Counseling of these couples after chorionic villus sampling should not focus on the specific CNV involved, but on the nature of mosaicism and the option of amniocentesis and ultrasound., (© 2021 John Wiley & Sons Ltd.)

Objective: Placental mosaicism for a subset of a chromosome, a structural chromosomal aberration, is thought to be a very rare finding in chorionic villus samples. Here, we present clinical and laboratory data on five cases with such mosaicism for structural chromosomal aberrations., Methods: During a period of 6 months, chromosomal microarray was carried out on DNA extracted from 100 uncultured chorion villous samples from high-risk pregnancies., Results: In five of 100 consecutively collected samples (5/100), mosaicism for a structural chromosomal aberration was detected. The mosaic aberration was subsequently detected in fetal tissue in three of the five cases., Conclusion: Chromosomal microarray can detect placental mosaicism for structural chromosomal aberrations. This kind of mosaicism may be more frequent than previously anticipated, and the fetal involvement seems difficult to predict. These findings highlight the complexity of mosaicism for structural chromosomal aberrations in prenatal samples in the chromosomal microarray era., Competing Interests: Declaration of competing interest No conflict of interest to be declared for any of the authors., (Copyright © 2019. Published by Elsevier Masson SAS.)

Stickler syndrome, a clinically as well as molecularly heterogeneous connective tissue disorder, is predominantly inherited in an autosomal dominant manner and is considered complete penetrant. Previously, mosaicism in Stickler syndrome has been reported in only a few cases. We describe a child with Stickler syndrome due to a novel splice site mutation in COL11A1. Initially, Sanger sequencing of both parents showed normal test results for the mutation. Due to mild phenotypic traits, the father was tested again using a more sensitive method (NGS), and was found to have low-grade mosaicism in various tissue samples (range 7-22% of the DNA). Therefore, we recommend using sensitive genetic testing when mosaicism is suspected. Furthermore, we support previous suggestions of parental testing even when the parents of an affected patient do not have obvious phenotypic signs of Stickler syndrome., (Copyright © 2017 Elsevier Masson SAS. All rights reserved.)