Residual risk for cytogenetic abnormalities after prenatal diagnosis by interphase fluorescence in situ hybridization (FISH)

Evaluation of the practical applications of fluorescence in situ hybridization in the prenatal diagnosis of positive noninvasive prenatal screenings

OBJECTIVE

To investigate the application value and limitations of fluorescence in situ hybridization (FISH) in prenatal diagnosis of positive results for trisomies 13, 18, 21 (T13, T18, T21) and sex chromosome aneuploidies (SCAs) indicated by noninvasive prenatal screening (NIPS).

METHODS

Samples from women who underwent prenatal diagnosis for the indication of positive NIPS of T13, T18, T21, and SCAs were collected. Each sample was split into two for both karyotype analysis and FISH analysis. The efficiency and consistency of FISH were assessed for the detection of chromosome abnormalities in the indications of positive NIPS results compared with karyotyping.

RESULTS

A total of 649 pregnant women who scored positive for clinical significance of fetal chromosome abnormalities by NIPS were enrolled in our study, including T 13 (6%), T18 (14.3%), T21 (44.7%), SCAs (35.0%). From the following diagnostic test, the positive predictive value (PPV) of NIPS for T13, T18, T21, and SCAs was 17.9, 60.2, 89.3, and 43.6% respectively. FISH analysis was successful in all samples. Compared with karyotyping, the sensitivity and specificity were 98.3 and 100%, respectively. 95.7% (621/649) were fully concordant with karyotyping. 3.2% (21/649) cases were incompletely concordant with the karyotyping, among these cases, the FISH analysis identified all the aneuploidies, but karyotyping analysis provided more information about the chromosomal structure. There were 7 cases (1.1%, 7/649) of anomalies diagnosed by karyotype but missed out by FISH, all of which occurred in cases with the indication of SCAs. If the indications were confined to cases with a positive NIPS of T13, T18, T21, the diagnostic consistency of the two methods almost perfectly agree, and all the aneuploidies were detected by the FISH assay. FISH analysis was highly consistent in determining whether the fetus was euploid or not in the prenatal diagnosis for the patients with positive NIPS results compared with karyotyping (kappa= 0.976, p < .01).

CONCLUSION

For the prenatal diagnostic indications of positive NIPS of T13, T18, T21, and SCAs, FISH was equally efficacious in identifying aneuploidies and provided a quick diagnosis to alleviate anxiety. However, the missed risk of FISH analysis for structural chromosomal abnormalities should be taken seriously and fully informed during genetic counseling.

Rapid aneuploidy screening (FISH or QF-PCR): the changing scene in prenatal diagnosis?

The accuracy of new molecular diagnostics, fluoresence in situ hybridization or quantitative fluorescence-PCR (collectively known as rapid aneuploidy screening), in prenatal diagnosis has already been demonstrated in a number of large studies. The challenge now is how to apply them clinically in the most cost-effective manner. It is now time to appraise whether rapid aneuploidy screening can replace traditional karyotyping when amniocenteses are performed for increased risk of Down's syndrome by maternal serum screening or advanced maternal age in the absence of ultrasound abnormality. The ten most recent studies from the literature within this research theme are reviewed and the pros and cons of this new approach in prenatal diagnosis are discussed, including the suggestion of future studies.

Rapid aneuploidy testing versus traditional karyotyping in amniocentesis for certain referral indications

OBJECTIVE

(1) To determine the suitability of replacing full karyotype analysis with quantitative fluorescent polymerase chain reaction (QF-PCR) for prenatal diagnosis in amniotic fluid samples obtained by amniocentesis. (2) To evaluate an indication-based classification of cases at risk of missing clinically relevant chromosomal disorders by QF-PCR.

METHODS

We reviewed all fetal karyotypes obtained by amniocentesis between January 2004 and December 2008. We compared the cytogenetic findings obtained through conventional karyotype with those that would have been theoretically obtained using QF-PCR.

RESULTS

Of the 4007 karyotypes obtained, 110 abnormal karyotypes were found (2.8%). Out of these, 30 (27%) were chromosomal abnormalities (CA) which would not have been detected by PCR alone. These included 16 cases (53%) predicted to confer no increased risk, 9 (30%) predicted to have a low risk, and 5 (17%) with an uncertain or high risk of fetal abnormality. A policy of QF-PCR alone would have identified 80 of 85 (94%) clinically significant CA. When QF-PCR shows a normal result, the overall residual risk is 0.75% for any CA and 0.12% for a clinical significant CA.

CONCLUSION

In our population, a policy of QF-PCR alone would miss 0.12% clinically relevant CA. QF-PCR directed to common aneuploidies can be considered as an economically and clinically acceptable prenatal diagnosis policy, offering full karyotype only for specific indications.

Rapid diagnosis of fetal chromosomal abnormalities by fluorescence in situ hybridization

A Down-kór noninvazív, maternális szűrése során azonosított fokozott kockázatú esetekben a magzati aneuploidiák diagnosztizálására gyors molekuláris módszerek állnak rendelkezésre, ezek diagnosztikus értéke azonban vitatott. Célkitűzés: A szerzők a prospektív vizsgálattal adatokat kívántak szerezni arra a kérdésre, hogy milyen a megbízhatósága az egyik gyors tesztnek, az interfázis fluoreszcens in situ hibridizációnak (FISH). Módszerek: 2002. május és 2006. szeptember között az összes beérkezett 1279 magzati mintát megvizsgálták mind interfázis-FISH-sel, mind tenyésztést követő kariotipizálással. Eredmények: Interfázis-FISH-vizsgálattal 47 esetben (3,7%) észleltek többlet- vagy hiányzó szignált (32 esetben 21-triszómia, 15 esetben egyéb számbeli rendellenesség), ezek mindegyike megegyezett a tenyésztés során talált eredménnyel. Tizenkilenc esetben interfázis-FISH-sel normális eredményt kaptak, azonban a tenyésztés után nyert készítményekben rendellenesség mutatkozott (a 19-ből 12-ben kiegyensúlyozott transzlokáció). Tovább elemezve ezeket az eseteket, azt az eredményt kapták, hogy az 1279 terhességből 4 (0,3%) volt olyan (3 magzat szám feletti kromoszómával, 1 kiegyensúlyozatlan de novo transzlokációval), amelyből új mutációval rendellenes fenotípusú újszülött született volna, ha nem készül metafázisos vizsgálat. A 4-ből kettőben kóros magzati ultrahangjelek mutatkoztak. Következtetés: Noha további összehasonlító elemzésekre van szükség, a szerzők véleménye szerint a Down-szindróma szűrési protokolljában az interfázis-FISH kizárólagos alkalmazása a diagnosztikus fázisban elfogadható lehet, ha ezt csupán emelkedett anyai életkor és az anyai szérummarkerek alapján kiszűrt esetekben alkalmazzák. Amennyiben az indikáció familiáris transzlokáció vagy 2. trimeszterbeli kóros ultrahanglelet, a metafázisos készítmények értékelésére van szükség.

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.

Quantitative Fluorescent Polymerase Chain Reaction versus Cytogenetics: Risk-Related Indication and Clinical Implication of Nondetected Chromosomal Disorders

BACKGROUND

The rapid detection of aneuploidies by quantitative fluorescent polymerase chain reaction (QF-PCR) allows reliable prenatal diagnosis of trisomies 21, 18, and 13. Discussion has been raised as to whether single QF-PCR could be an alternative to traditional cytogenetic karyotyping for certain referral categories.

OBJECTIVE

To evaluate an indication-based classification of cases at risk of missing clinically relevant chromosomal disorders by QF-PCR.

METHODS

From October 1999 to November 2003, 4,682 of 14,123 patients referred for amniocentesis decided to have QF-PCR as a rapid adjunct to conventional cytogenetic evaluation. Patients were classified according to the risk of missing chromosomal abnormalities by QF-PCR based on anamnestic risk and ultrasound prior to amniocentesis. The results in these two defined categories were compared in relation to the clinical significance of cytogenetic results.

RESULTS

QF-PCR and conventional cytogenetic analysis had concordant results in 4,617 of 4,682 (98.6%) cases. Thirty-six of 110 (32.2%) clinically significant chromosomal abnormalities were missed by QF-PCR. Patients classified not to be at risk of missing chromosomal abnormalities using QF-PCR had a residual risk of 1/166 (0.6%) for chromosomal distortions of clinical significance.

CONCLUSION

Classification by anamnestic and sonographic data does not specifically identify patients at risk of structural abnormalities. Clinical relevance of the nondetected anomalies essentially justifies traditional karyotyping regardless of risk classification.

Correlation of Abnormal Rapid FISH and Chromosome Results from Amniocytes for Prenatal Diagnosis

Rapid fluorescence in situ hybridization (FISH) performed on 1,788 amniocenteses, using Aneuvision (Vysis) probes for chromosomes 13, 18, 21, X, and Y, over several years, yielded 115 cases with percentages of aneuploidy between 4 and 100%. All cases above 60% were confirmed to be positive by chromosome analysis. Fifteen of forty-one cases that would be considered inconclusive by generally accepted criteria (i.e. with less than 60% of cells with an abnormal signal pattern) revealed lower cutoffs to be positive when confirmed by chromosome analysis. For trisomy 21, 6 cases with percentages from 36 to 57% were positive; 4 of 7 cases with percentages from 22.5 to 33% were positive; 11 cases with percentages of 13% or less were negative. Similar trends were found for aneuploidies of 13, 18, X, and Y. However, the number of abnormal cases is still too small to determine definitive cutoffs in the <60% gray zone. An average of 57 metaphases was analyzed for cases with FISH percentages below 60%. Despite the wide range of abnormal FISH percentages for chromosomally positive cases, we found no examples of autosomal mosaicism in this series. Although sex chromosome mosaicism was cytogenetically evident in several cases, there was little direct correlation between cytogenetic and rapid FISH results. FISH results involving sex chromosomes were more frequently confounded by maternal cell contamination and other technical factors.

Fetal reduction

Fetal Reduction has been employed over the past two decades as a mechanism to reduce the morbidity and mortality of multiple pregnancies. Utilization of the procedure has increased dramatically as IVF has become commonplace but the average starting number has decreased with the transfer of fewer embryos. Success rates from fetal reduction have improved as a function of increasing experience, better ultrasound, and lower starting numbers. Genetic diagnosis prior to reduction can improve the overall outcomes. Reduction of triplets or more clearly improves outcomes, and reduction of twins to a singleton is now a reasonable consideration.

Rapid prenatal diagnostic testing for Down syndrome only or longer wait for full karyotype: the views of pregnant women

OBJECTIVES

Prenatal diagnosis by karyotype analysis determines the copy number and structure of each chromosome and is considered to be the 'gold standard' in detection of chromosome abnormality. This method is, however, time consuming and women may have to wait up to 21 days for the results. With improving molecular genetic techniques, the most commonly occurring chromosome abnormalities can be diagnosed within 2 days from amniotic fluid. This study investigates the value pregnant women place on these alternative prenatal diagnostic tests.

METHODS

A structured self-completion discrete choice experiment questionnaire was designed. The subjects were 40 pregnant women, of unknown risk, attending for their 11-week booking scan and 10 elevated-risk women attending for amniocentesis at the Aberdeen Maternity Hospital, Scotland.

RESULTS

Women value 'comprehensive' information of a full karyotype analysis at pounds 791, and 'simple' information of a rapid diagnostic test at pounds 690. Willingness to pay for a day's reduction in waiting time for results is pounds 18. Women prefer a prenatal service providing simple over comprehensive information as long as they receive results 6 days sooner than the comprehensive results would be provided.

CONCLUSIONS

While women prefer comprehensive information, the bulk of the value is placed on knowing whether the fetus has Down syndrome. Given the longer wait times for comprehensive information, simple information is preferred as long as results are received 6 days sooner than would be the case for comprehensive information. These results have implications for the resources dedicated to providing a rapid prenatal diagnostic service.

Update on selective reduction

Over the past 25 years fetal reduction has been utilized to reduce the risks of higher-order multiple pregnancies that have resulted from overly successful infertility therapies. The demographics of multiple pregnancy patients have evolved over the past decade, with increasing proportions coming from IVF as opposed to ovulation induction, being older and a higher proportion with donor eggs. Genetic diagnosis prior to reduction is becoming more common and is very safe in experienced hands. For all starting numbers, including twins, reduction to a lower number of fetuses reduces fetal losses, prematurity, and infant mortality and morbidity.

Prenatal diagnosis by rapid aneuploidy detection and karyotyping: a prospective study of the role of ultrasound in 1589 second-trimester amniocenteses

BACKGROUND

Reliable methods are available for rapid aneuploidy detection (RAD) for the prenatal diagnosis of trisomies 21, 18 and 13. This study examines the potential advantages and limitations of using RAD as a replacement rather than as an adjunct to traditional karyotyping.

METHODS

One thousand five hundred and eighty-nine consecutive pregnancies referred for cytogenetic assessment were offered RAD (FISH or QF-PCR) as an adjunct to traditional karyotyping. The results of these two processes were compared, and the effects of three policies for cytogenetic evaluation were determined: RAD alone, a combination of RAD for all and traditional karyotyping for cases with ultrasound anomalies or a policy of RAD and traditional karyotyping in all cases.

RESULTS

RAD was uninformative because of maternal-cell contamination in 37 (2.3%) cases compared to 4 (0.3%) cases of culture failure in traditional karyotyping. RAD and traditional karyotyping results were concordant in 1526 of 1548 (98.6%) cases. All non-mosaic cases of trisomies 21, 18 and 13 and cases of triploidy were correctly identified by RAD, and there were no false-positive diagnoses. The gold standard of a traditional karyotype in each case would have detected all chromosomal abnormalities. A policy of RAD alone would have identified 60 of 73 (82%) clinically important chromosomal abnormalities. The addition of a full karyotype for cases with evidence of ultrasound abnormalities would have improved detection to 95%.

CONCLUSION

A policy offering RAD to all patients, but restricting traditional karyotyping to cases with ultrasound anomalies, would reduce the number of traditional karyotypes requested by 70%, but maintain a 95% detection rate for all clinically important chromosomal abnormalities. Further studies are required to determine whether similar results could be obtained in district general hospital units and to determine whether this approach would be acceptable to health professionals and patients.