Amniotic fluid interphase fluorescence in situ hybridization (FISH) for detection of aneuploidy; experiences in 130 prenatal cases

The importance of rapid aneuploidy screening and prenatal diagnosis in the detection of numerical chromosomal abnormalities

Objectives

Evaluation of Fluorescent in situ hybridization (FISH) as a tool for rapid aneuploidy screening (RAS) of high risk pregnancies, before its approval in the national antenatal screening and genetic diagnosis program in Egypt.

Methods

The cytogenetic data of prenatal specimens, and results of FISH of 100 patients performed between, January 2009 and December 2009, at the Medical Genetics Center (MGC) laboratory were retrieved and reviewed. AneuVysion Assay kit was used for detection of 13, 21, X, Y, 18 aneuploidies.

Results

Maternal age varied from 21 to 44 years (mean was 35.6 year). Ninety percent of pregnancies had normal chromosomes and 10% of the cases had numerical chromosomal abnormalities. Trisomy 21 was the most frequent chromosomal disorder across all indications (5%), followed by Turner syndrome (2%), trisomy 18 (2%), and trisomy 13 (1%). When comparing the FISH data with karyotype results for chromosomes 13, 18, 21, X, and Y in the 83 individual tested, no false positive or negative results were detected by the FISH assay. The result obtained by FISH and the banding cytogenetic were in complete accordance.

Conclusion

This study supports the integration of amniotic fluid (AF) FISH as a RAS test, in to routine antenatal practice for identification of chromosome aneuploidies. There are trends towards delayed childbearing and most cases of Down Syndrome (DS) are currently detected post-nataly in the Egyptian population. Consequently, the live birth prevalence of DS has increased, which might lead to a serious negative public health effects.

The importance of screening and prenatal diagnosis in the identification of the numerical chromosomal abnormalities

BACKGROUND AND AIMS

The obstetric care of a pregnancy, as it is practiced today, includes non-invasive screening approaches as well as invasive procedures for the definitive prenatal diagnosis of fetal disorders correlations between indications for prenatal cytogenetic diagnosis and results of the chromosomal analysis made upon fetal cells. The aim of our study was to evaluate the correlations between the screening test results and results of chromosomal analysis on fetal cells.

METHODS

Amniotic fluid samples from 1159 pregnant women were studied with the rapid FISH method and the cytogenetic analysis (karyotype). The results from both methods were compared.

RESULTS

The indications to perform prenatal cytogenetic diagnosis for numerical chromosomal abnormalities were: abnormal results of double or triple test, advanced maternal age, fetal abnormality detected through ultrasound examination, and positive family history for chromosomal anomalies. In our study we identified 30 cases with abnormal numeric chromosomes (18 cases of trisomy 21, 4 cases of trisomy 18, 3 cases of trisomy X, 1 case of monosomy, 2 cases of trisomy XYY, 1 case of trisomy XXY and 1 case of triploidy).

CONCLUSIONS

This report confirms the importance of screening and the cytogenetic diagnosis in the identification of the numerical chromosomal abnormalities.

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.

Advanced maternal age as an indication for preimplantation genetic diagnosis (PGD)--the need for more judicious application in clinically assisted reproduction

BACKGROUND

Pre-implantation genetic diagnosis (PGD) is often recommended for routine screening of chromosomal aneuploidy in older women undergoing clinical assisted reproduction, even though its prognostic value on this group of patients is rather ambiguous. What is needed is a clear set of ethical guidelines in the marketing of this technically complex and expensive procedure to patients who are neither suffers nor carriers of serious genetic diseases.

METHODS

Professional counseling would be required to enable an informed decision from the patient. Differences in the prognostic value of PGD for different medical indications must be clearly presented to the patient and they must also be told that PGD is not a completely 'fool-proof' means of preventing birth defects. What may be detected are some genetic syndromes and conditions associated with cytogenetic abnormalities.

RESULTS

The patient must be made aware that the results of previous studies have demonstrated that the overwhelming majority of chromosomally abnormal oocytes and embryos either fail to fertilize or implant, and therefore have a relatively low chance of resulting in a live birth with chromosomal defects. Statistical data, particularly the concept of relative risk must clearly be presented to the patient without exaggerating the risk of birth defects. The patient must also be rightfully informed that PGD carries a small risk of damaging the embryo, which could compromise chances of conception.

CONCLUSIONS

PGD should be judiciously indicated for advanced maternal age in clinically assisted reproduction. Other diagnostic options that may be cheaper, and which also possess a high level of accuracy should be presented first to the patient i.e. amniocentesis, chorionic villus biopsy and ultrasonargraphy.

Automatic Scanning of Interphase FISH for Prenatal Diagnosis in Uncultured Amniocytes

Fluorescence in situ hybridization (FISH) of uncultured amniocytes using chromosome-specific DNA probes offers the opportunity for rapid aneuploidy screening. Between 80 and 95% of all chromosomal disorders expected in the second trimester of pregnancy can be discovered within 24 hr if DNA probes specific for chromosomes 21, 18, 13, X, and Y are used. Rapid results are crucial for clinical decision-making and are helpful in decreasing the anxiety level in most patients. One of the major factors that have been preventing the rapid FISH test from being broadly incorporated into the clinical setting is the limited staff in the cytogenetics laboratories. The present study demonstrates the use of an automated scanning system (Duet, BioView Ltd. Rehovot, Israel) for analyzing FISH in uncultured amniocytes. Fifty-six amniotic fluid samples were evaluated in parallel by karyotyping, manual FISH analysis, and automatic FISH scanning. Automatic scanning provided accurate results compared to both manual FISH scoring and karyotype analysis. The correlation between automatic and manual FISH scanning was found to be very high (r = 0.9, p < 0.0001). The availability of automation for aneuploidy screening in amniotic fluid samples will enable offering this test to a broader patient population while providing fast and reliable results.