The isochromosome 20q abnormality of pluripotent cells interrupts germ layer differentiation.

Chromosome 20 abnormalities are some of the most frequent genomic changes acquired by human pluripotent stem cell (hPSC) cultures worldwide. Yet their effects on differentiation remain largely unexplored. We investigated a recurrent abnormality also found on amniocentesis, the isochromosome 20q (iso20q), during a clinical retinal pigment epithelium differentiation. Here we show that the iso20q abnormality interrupts spontaneous embryonic lineage specification. Isogenic lines revealed that under conditions that promote the spontaneous differentiation of wild-type hPSCs, the iso20q variants fail to differentiate into primitive germ layers and to downregulate pluripotency networks, resulting in apoptosis. Instead, iso20q cells are highly biased for extra-embryonic/amnion differentiation following inhibition of DNMT3B methylation or BMP2 treatment. Finally, directed differentiation protocols can overcome the iso20q block. Our findings reveal in iso20q a chromosomal abnormality that impairs the developmental competency of hPSCs toward germ layers but not amnion, which models embryonic developmental bottlenecks in the presence of aberrations.

Mosaic isochromosome 20q at amniocentesis: Prenatal diagnosis, genetic counseling and literature review.

OBJECTIVE: We present prenatal diagnosis of mosaic isochromosome 20q [i(20q)] at amniocentesis, and we review the literature. CASE REPORT: A 36-year-old woman underwent amniocentesis at 17 weeks of gestation because of advanced maternal age. Amniocentesis revealed a karyotype of 46,XY,i(20)(q10)[27]/46,XY[29]. Prenatal ultrasound findings were unremarkable. The parental karyotypes were normal. Repeat amniocentesis was performed at 20 weeks of gestation. During repeat amniocentesis, array comparative genomic hybridization (aCGH), interphase fluorescence in situ hybridization (FISH) and quantitative fluorescent polymerase chain reaction (QF-PCR) assay were performed on uncultured amniocytes, and conventional cytogenetic analysis, interphase FISH and aCGH were performed on cultured amniocytes. In the repeat amniocentesis, the cultured amniocytes revealed a karyotype of 46,XY. Interphase FISH analysis showed the i(20q) signal in 5.2% (5/96) of the uncultured amniocytes compared with 2% in the control, and in 0.98% (1/102) of the cultured amniocytes compared with 2% in the control. aCGH detected no genomic imbalance in both uncultured and cultured amniocytes. QF-PCR analysis excluded uniparental disomy 20. At 38 weeks of gestation, a healthy 2870-g male baby was delivered with no phenotypic abnormality. The postnatal blood karyotype was 46,XY. FISH analysis on urinary cells showed 2.1% (2/95 cells) mosaicism compared with 1.9% (2/105 cells) in the control. CONCLUSION: Mosaic i(20q) at amniocentesis is a benign condition associated with a favorable outcome in most cases and can be a cell culture artifact confined to cultured amniocytes. Molecular cytogenetic analysis using uncultured amniocytes is useful for rapid confirmation. Prenatal diagnosis of very high percentage of mosaicism for i(20q) at amniocentesis should alert the presence of fetal structural abnormalities. Prenatal diagnosis of mosaic i(20q) at amniocentesis should include a detail examination of fetal brain and spine.

Prenatal diagnosis of isochromosome 20q in a fetus with vertebral anomaly and rocker-bottom feet.

OBJECTIVE: Isochromosome of the long arm of chromosome 20 (i(20q)) is a rare structural abnormality in prenatal diagnosis. Thirty prenatal cases of mosaic i(20q) have been reported, among which only four are associated with fetal malformations. We describe a new prenatal case of i(20q) with fetal malformations. MATERIALS AND METHODS: We also observed a discrepancy between uncultured and cultured amniotic fluid cells by using conventional cytogenetic, fluorescence in situ hybridization and array-SNP analysis. RESULTS: The short arm deletion of chromosome 20 arising from the isochromosome encompassed two candidate genes PAX1 and JAG1 involved in cranio-facial and vertebral development. CONCLUSION: The data would allow establishing a phenotype-genotype correlation. Thus, we proposed to define a recognizable syndrome combining cranio-facial dysmorphism, vertebral bodies' anomalies, feet and cerebral malformations.

Detection of no isochromosome 20q by interphase fluorescent in situ hybridization on uncultured amniocytes in a pregnancy with mosaic isochromosome 20q in cultured amniocytes at amniocentesis.

OBJECTIVE: To present prenatal diagnosis and molecular cytogenetic characterization of mosaic isochromosome 20q at amniocentesis. MATERIALS AND METHODS: A 36-year-old woman underwent amniocentesis at 17 weeks of gestation because of advanced maternal age, and conventional cytogenetic analysis revealed a karyotype of 46,XY,i(20)(q10)[12]/46,XY[7]. Repeated amniocentesis was performed at 20 weeks of gestation. During repeated amniocentesis, array comparative genomic hybridization (aCGH), interphase fluorescence in situ hybridization (FISH), and quantitative fluorescent polymerase chain reaction (QF-PCR) were performed on uncultured amniocytes, and conventional cytogenetic analysis and interphase FISH were performed on cultured amniocytes. RESULTS: Conventional cytogenetic analysis of cultured amniocytes revealed a karyotype of 46,XY,i(20)(q10)[4]/46,XY[16]. Interphase FISH analysis on 217 uncultured amniocytes did not detect isochromosome 20q, aCGH on the DNA extracted from uncultured amniocytes showed no genomic imbalance, and QF-PCR analysis on the DNA extracted from uncultured amniocytes excluded uniparental disomy 20 (UPD 20). Interphase FISH analysis on 115 cultured untouched amniocytes revealed 13% (15/115 cells) mosaicism for isochromosome 20q. CONCLUSION: Mosaic isochromosome 20q detected at amniocentesis can be a cell culture artifact. Detailed ultrasound examination, performing interphase FISH and/or aCGH on uncultured amniocytes for confirmation of true mosaicism, and performing QF-PCR to exclude UPD 20 may be useful under such a circumstance.