French multi-centric study of 2000 amniotic fluid interphase FISH analyses from high-risk pregnancies and review of the literature

Avoiding a second amniocentesis to corroborate prenatal diagnosis by using refrigerated samples

OBJECTIVE

This study is aimed to probe the usefulness of refrigerated aliquots of amniotic fluid to be used for fluorescence in situ hybridization (FISH) in order to perform an accurate prenatal diagnosis avoiding the risk related to an additional amniocentesis procedure and the psychological stress to the pregnant woman and her family.

METHODS

Non-cultured amniotic fluid (AF) samples were analyzed by FISH. Such samples were divided into two groups. The first one included fresh collected AF (FCAF, N = 30). The second one included refrigerated samples of AF (RSAF, N = 12) to corroborate uncertain chromosome aberration identification obtained by conventional methods. Sample refrigeration did not exceed 18 days.

RESULTS

No differences were found between groups. In the RSAF group, three cases of chromosomal mosaicismo and seven cases of pseudomosaicism were corroborated. No alteration adjudicated to aberrant chromosomal line presence was found in born children according to genetic specialists' criteria. In the two remaining cases, applied procedure allowed elucidating fetal sex in one case and the origin of a marker chromosome in the other.

CONCLUSIONS

Amniocytes obtained from RAFS are a useful biological material to be assayed by FISH, achieving an accurate prenatal diagnosis and avoiding an additional amniocentesis.

Rapid-prenatal diagnosis through fluorescence in situ hybridization for preventing aneuploidy related birth defects

BACKGROUND AND OBJECTIVE:

Women with high-risk pregnancies are offered prenatal diagnosis through amniocentesis for cytogenetic analysis of fetal cells. The aim of this study was to evaluate the effectiveness of the rapid fluorescence in situ hybridization (FISH) technique for detecting numerical aberrations of chromosomes 13, 21, 18, X and Y in high-risk pregnancies in an Indian scenario.

MATERIALS AND METHODS:

A total of 163 samples were received for a FISH and/or a full karyotype for prenatal diagnosis from high-risk pregnancies. In 116 samples both conventional culture techniques for getting karyotype through G-banding techniques were applied in conjunction to FISH test using the AneuVysion kit (Abbott Molecular, Inc.), following standard recommended protocol to compare the both the techniques in our setup.

RESULTS:

Out of 116 patients, we got 96 normal for the five major chromosome abnormality and seven patients were found to be abnormal (04 trisomy 21, 02 monosomy X, and 01 trisomy 13) and all the FISH results correlated with conventional cytogenetics. To summarize the results of total 163 patients for the major chromosomal abnormalities analyzed by both/or cytogenetics and FISH there were 140 (86%) normal, 9 (6%) cases were abnormal and another 4 (2.5%) cases were suspicious mosaic and 10 (6%) cases of culture failure. The diagnostic detection rate with FISH in 116 patients was 97.5%. There were no false-positive and false-negative autosomal or sex chromosomal results, within our established criteria for reporting FISH signals.

CONCLUSION:

Rapid FISH is a reliable and prompt method for detecting numerical chromosomal aberrations and has now been implemented as a routine diagnostic procedure for detection of fetal aneuploidy in India.

Proportion of parents agreeing to delay fetal karyotyping until the third trimester of pregnancy in cases with an indication

OBJECTIVE

To assess the extent to which couples who could benefit from fetal karyotyping during the first or second trimester would agree to delay the examination until the third trimester.

METHODS

In this prospective monocentric study, the same physician suggested to some couples to delay fetal karyotyping until the third trimester.

RESULTS

458 couples participated in this study. 230 couples (230/458 = 50.2%) refused to delay the examination until the third trimester of pregnancy (group 1). For these patients, four chromosomal abnormalities led to the termination of pregnancy. Fifty-six couples (56/458 = 12.2%) who initially agreed to delay the fetal karyotyping later changed their minds (group 2). 104 couples (104/458 = 22.7%) agreed to delay the examination (group 3). For these patients, one trisomy 21 was diagnosed and led to the subsequent termination of the pregnancy at 33 weeks of amenorrhea. Sixty-eight couples (68/458 = 14.8%) refused any form of invasive prenatal diagnosis (group 4). There was no difference in the rate of preterm premature rupture of membranes, pregnancy term, premature birth rate and birth weight between the four groups.

CONCLUSIONS

Our study reports that about a quarter of couples did indeed agree to delay fetal karyotype assessment until the third trimester of pregnancy.

Rapid and novel prenatal molecular assay for detecting aneuploidies and microdeletion syndromes

OBJECTIVES

To develop a targeted aneuploidy and microdeletion detection platform for use in the prenatal setting, to assess the integrity of the platform with a robust validation system, and to prospectively determine the performance of the platform under routine clinical conditions.

METHODS

To generate proxies for the various disorders assessed by the assay for analytical validation purposes, cells from ten microdeletion syndromes as well as from common aneuploidies were spiked into cleared amniotic fluid. Genomic DNA was isolated, labeled, and hybridized to microbeads that have been coupled to DNA derived from Bacterial Artificial Chromosome (BAC) from the relevant regions targeted by the array. Beads were read using a flow cytometric multiplex bead array detection system. In the prospective part of the study, 104 amniotic fluid samples were collected and analyzed.

RESULTS

All microdeletion syndromes and aneuploidies were validated in a blinded fashion. In the prospective study, the total number of readable samples was 101 of 104 (97%). All sample results were confirmed independently.

CONCLUSION

The bead array approach is a rapid and reliable test for detecting aneuploidies and microdeletions. This assay has the potential to provide the benefit of expanded molecular cytogenetic testing to pregnant women undergoing invasive prenatal diagnosis. This approach may be especially useful in parts of the world where cytogenetic personnel and facilities may be limited.

Familial 18 centromere variant resulting in difficulties in interpreting prenatal interphase FISH

We report here on a familial case of centromeric heteromorphism of chromosome 18 detected by prenatal interphase fluorescence in situ hybridization (FISH) analysis transmitted by the mother to her fetus, and resulting in complete loss of one 18 signal. The prenatal diagnosis was performed by interphase FISH (AneuVysion probe set, and LSI DiGeorge 22q11.2 kit) because of the presence of an isolated fetal cardiac abnormality, and was first difficult to interpret: only one centromeric 18 signal was detectable on prenatal interphase nuclei, along with one signal for the Y and one for the X chromosome. The LSI DiGeorge 22q11.2 kit also showed the absence of one TUPLE 1 signal on all examined nuclei. In fact, the FISH performed on maternal buccal smear displayed the same absence of one chromosome 18 centromeric signal, combined with the presence of two TUPLE1 signals. All these results led to the diagnosis of an isolated 22q11.2 fetal microdeletion that was confirmed on metaphases spreads. This case illustrates once again that the locus specific (LSI) probes are more effective than the alpha centromeric probes for interphase analysis. The development of high-quality LSI probes for chromosomes 18, X and Y could avoid the misinterpretation of prenatal interphase FISH leading to numerous additional and expensive investigations.

Difficult diagnosis and management of an heterokaryotypic monochorionic twin pregnancy with discordant fetal sex and 45,X/47,XYY karyotypes

We report twins for whom ultrasound examinations revealed a Turner syndrome in the female fetus and a normal male fetus. A selective pregnancy termination was decided on the female fetus with hydrops. The death of both twins called in question the chorionic diagnosis. Amniotic fluid cytogenetic analysis revealed a 45,X karyotype in the female twin and a 47,XYY karyotype in the male twin. Molecular cytogenetic analysis on genital and renal cells showed different levels of 45,X/47,XYY mosaicism in both twins; molecular analysis on the amniocytes showed monozygosity. Monozygotic twins with discordant sex are very rare. This study showed the difficult diagnosis and management of a monochorionic twin pregnancy with discordant fetal sex.

FastFISH: technique for ultrarapid fluorescence in situ hybridization on uncultured amniocytes yielding results within 2 h of amniocentesis

Rapid aneuploidy detection methods allow prenatal diagnosis results to be released within 48 h, but not on the same day as the invasive test. We aimed to develop a rapid fluorescence in situ hybridization (FISH) method (FastFISH) that releases accurate results on the same day as amniocentesis. FastFISH was optimized to be completed within 2 h of sample collection using CEP and LSI probes for chromosomes 13, 18, 21, X, Y and DiGeorge syndrome (DGS). The technique was tested on 100 consecutive amniotic fluid samples in a blinded study. It was also validated as a 1-day molecular genetic test on three representative fetal tissue samples: chorionic villus, amniotic fluid and fetal blood. In the blinded study, FastFISH results were ready within 2 h of sample collection. Of the 100 amniotic fluid samples, 49 male and 50 female fetuses were identified. One fetus was 47, XXY (Klinefelter syndrome). Three fetuses had trisomy 21. One fetus suspected of DGS by ultrasound was identified as normal. Results of FastFISH analyses in all 100 cases were concordant with their karyotypes (100% accuracy; lower 95% CI, 97.05%). In the 1-day test validation, all results were released on the same day and were concordant with their respective karyotypes. FastFISH allows results to be released on the same day as amniocentesis. It represents the necessary development for a 1-day prenatal diagnosis service.

Molecular cytogenetic and rapid aneuploidy detection methods in prenatal diagnosis

Cytogenetic analysis is an important component of prenatal diagnosis. The ability to rapidly detect aneuploidy and identify small structural abnormalities of fetal chromosomes has been greatly enhanced by the use of molecular cytogenetic technologies. In this review, we will present some of the molecular cytogenetic techniques available to the clinical cytogenetics laboratory. These include fluorescence in situ hybridization (FISH), quantitative fluorescence PCR (QF-PCR), multiplex ligation-dependent probe amplification (MLPA) and microarray-based comparative genomic hybridization (array CGH). The benefits and limitations of each technology will be discussed in the context of prenatal diagnosis.

[Molecular chromosomic genetics in prenatal and perinatal diagnosis of chromosomal anomalies and genetic diseases]

Prenatal and perinatal diagnosis needs a rapid, accurate and overall genome analysis. Molecular chromosomic techniques such as fluorescent in situ hybridization (FISH) with "cold" (not radioactively labeled) probes combine techniques of both conventional chromosome banding and molecular biology. FISH is a powerful tool for detecting some genetic diseases as well as microscopic or submicroscopic chromosome rearrangements, in metaphases cells or interphase nuclei.