Prenatal diagnosis of trisomy 8 mosaicism in CVS after abnormal ultrasound findings at 12 weeks

Case report: Prenatal diagnosis of rare chromosome mosaicism: discordant results between chorionic villi and amniotic fluid samples

Objective: We described a unique case of near-negative chromosome mosaicism in chorionic villi but complete monosomy X in amniotic fluid. Methods: Chorionic villus sampling and amniocentesis were performed separately in the first and second trimesters. Chromosomal microarray (CMA) and rapid aneuploidy detection (QF-PCR and FISH) were performed on placental villi and uncultured amniotic fluid. After pregnancy termination, the placenta, umbilical cord, and fetal muscle tissues were sampled for FISH detection. Results: The CMA revealed a lower signal from chromosome X in chorionic villi, with a copy number of 1.85, implying the presence of mosaic monosomy X. However, the QF-PCR and FISH results were nearly normal. In uncultured amniotic fluid, CMA and rapid aneuploidy detection indicated complete monosomy X. Across different sampling points on the aborted fetus, the FISH results varied from normal, to mosaic, and then complete monosomy X. Conclusion: This case presents a rare and complex situation where sampling from uncultured chorionic villi indicated low-level chromosome mosaicism, while sampling from amniotic fluid revealed complete monosomy X. Although some of these discordant outcomes may be due to methodological limitations, we conclude that prenatal consultation should be combined with fetal ultrasound phenotype and genetic testing for a comprehensive evaluation of fetal genetic abnormalities.

Trisomy 8 mosaicism in the placenta: A Danish cohort study of 37 cases and a literature review

OBJECTIVE

To evaluate the risk of fetal involvement when trisomy 8 mosaicism (T8M) is detected in chorionic villus samples (CVS).

METHODS

A retrospective descriptive study of registered pregnancies in Denmark with T8M in CVS identified through a database search and a review of published cases of T8M found through a systematic literature search and inclusion of cross references. Pregnancies with T8M in CVS and no additional numerical chromosomal aberrations were included.

RESULTS

A total of 37 Danish cases and 60 published cases were included. T8M detected in a CVS was associated with fetal involvement in 18 out of 97 pregnancies (18.6% [95%CI: 11.4-27.7]). Eight out of 70 (11.4% [95%CI: 5.1-21.3]) interpreted prenatally to be confined placental mosaicism (CPM) were subsequently found to be true fetal mosaicisms (TFM).

CONCLUSION

T8M detected in CVS poses a significant risk of fetal involvement, and examination of amniotic fluid (AF) and/or fetal tissue should be offered. However, a normal result of AF still has a considerable residual risk of fetal involvement. Genetic counselling at an early gestational age is essential, and follow-up ultrasonography should be performed to predict fetal involvement if possible.

Prenatal detection of trisomy 8 mosaicism: Pregnancy outcome and follow up of a series of 17 consecutive cases

OBJECTIVE

To study the outcome of a series of individuals with prenatal detection of trisomy 8 mosaicism by chorionic villus sampling (CVS) and/or amniocentesis.

STUDY DESIGN

The databases of two Italian genetics units were reviewed to identify all consultations requested during pregnancy because of trisomy 8 mosaicism. To evaluate the pregnancy outcome, the regional registry of congenital malformations (including terminations of pregnancies) was consulted; additional follow-up data were collected by a telephone interview. The following outcomes were analysed: delivery, pre- and post-natal growth, psychomotor development, major malformations, other diseases/complications.

RESULTS

A total of 17 consecutive cases of trisomy 8 mosaicism were identified. Fourteen cases were first detected among women undergoing prenatal diagnosis by CVS; the remaining ones were identified among women who underwent amniocentesis. In most cases diagnosed by CVS, the chromosomal anomaly was only detected in long-term cell cultures (10/14) and was not confirmed by amniocentesis (11/13). There were two terminations of pregnancy and 15 live births; no major birth defects were observed among live born infants and only a case with prenatal and postnatal growth retardation was observed (mean age at follow-up interview was 5.9 years).

CONCLUSION

Our data showed an overall positive prognosis for cases with an apparent confined placental mosaicism and those with low-level mosaicism in amniotic fluid if no congenital anomalies were detected by foetal ultrasound examinations. However, larger studies are warranted to better define the associated risk of neurodevelopmental anomalies.

Prenatal diagnosis of mosaic tetrasomy 8p

Tetrasomy 8p is a rare chromosomal disorder that has only been detected in a mosaic form. At the present time, 11 cases have been reported; their phenotype included agenesis of the corpus callosum, enlarged ventricles, minor facial dysmorphism, rib and vertebral anomalies, and mild to moderate developmental delay. To the best of our knowledge, tetrasomy 8p has never been prenatally diagnosed. This 43-year-old woman was referred for amniocentesis at 20 weeks' gestation because of advanced maternal age. Amniotic fluid cells were cultured according to standard techniques by the in situ method. A supernumerary chromosomal marker was detected in a single clone of cultured amniotic cells and interpreted by RHG banding as an isochromosome of the short arm of chromosome 8 (i(8p)). The ultrasound investigation at 27 weeks gestation revealed enlarged ventricles and agenesis of the corpus callosum, which were confirmed at fetal autopsy after medical termination of the pregnancy. Chromosomal analyses, including RHG banding and FISH, of several tissues showed different levels of i(8p) mosaicism. Whereas no i(8p) was detected on cytotrophoblast nor additional amniotic fluid cells, 97% and 30% of cells from long-term cultures of placenta and lymphocytes, respectively, had the i(8p). Using DNA markers, the isochromosome 8p was interpreted as the result of a prezygotic event during maternal meiosis. Our findings suggest that the i(8p) is the subject of tissue selection. Tetrasomy 8p might be underdiagnosed during pregnancy; therefore, karyotyping on a fetal blood sample following detection of agenesis of the corpus callosum when no chromosomal abnormality has been found on the amniotic fluid cell cultures should be discussed with the parents.

Trisomy 8 mosaicism: selective growth advantage of normal cells vs. growth disadvantage of trisomy 8 cells

A fetus with trisomy 8 mosaicism was identified prenatally due to an abnormal maternal serum triple screen. Tissue samples were taken at birth to determine the level of trisomy 8 mosaicism found within embryonic and extra-embryonic tissues, rates of cell division for the two cell lines, and the effect of mosaicism on the phenotype. The level of trisomy 8 cells in blood and fibroblasts was higher than in placental tissue. Cell cycle kinetics, by incorporation of bromodeoxyuridine for 48 hr, was not significantly different between the trisomy 8 and normal cells for blood or amnion. Fluorescent in situ hybridization (FISH) using centromeric probe for chromosome 8 showed significantly more trisomy 8 in interphase vs. metaphase in lymphoblasts, umbilical cord fibroblasts, and chorion. The loss of trisomy 8 cells is not due to anaphase lag, as determined by micronuclei analysis. The similarity of cell cycle kinetics between trisomy 8 cells and normal diploid cells suggests some trisomy 8 cells are exiting the cell cycle prematurely. This growth disadvantage of trisomy 8 cells results in the appearance of growth advantage for diploid cells.

Management of prenatally detected trisomy 8 mosaicism

We report on ten pregnancies with trisomy 8 mosaicism. Nine cases were prenatally detected in chorionic villi (n=6), amniotic fluid (AF) cells (n=2) or fetal blood (FB) lymphocytes (n=1). Follow-up laboratory investigations showed confined placental mosaicism (CPM) or pseudomosaicism in eight cases. In one case with ultrasound abnormalities, trisomy 8 mosaicism was detected in FB cells although cultured AF cells showed normal cells only. Another case of mosaic trisomy 8 was prenatally missed; cytogenetic analysis of short-term cultured villi revealed a normal male karyotype, while postnatally, trisomy 8 mosaicism was detected in peripheral blood lymphocytes and skin fibroblasts of the affected child. These findings indicate the difficulties in the prenatal diagnosis of trisomy 8 mosaicism. When found in chorionic villi, it mostly represented CPM, while in a case of true fetal trisomy 8 mosaicism, the cytotrophoblast cells showed a normal karyotype. So, the cytotrophoblast compartment of chorionic villi is a poor indicator of the presence or absence of fetal trisomy 8 mosaicism. Follow-up investigations including amniocentesis and especially fetal blood sampling are required to come to a definite prenatal diagnosis of trisomy 8 mosaicism.

Prenatal diagnosis of mosaic trisomy 8 in a fetus with normal nuchal translucency thickness and reversed end-diastolic ductus venosus flow

We report a case of the prenatal diagnosis of trisomy 8 in a fetus presenting with normal nuchal translucency of 0.8 mm and reversed end-diastolic ductus venosus blood flow at a routine first-trimester scan at 11 weeks of gestation. No structural abnormalities were detected by the ultrasound scan. Karyotyping by chorionic villus sampling led to the diagnosis of mosaic trisomy 8, which was confirmed by fluorescent in-situ hybridization on fetal tissue samples.