Detection of maternal cell contamination in amniotic fluid cell cultures using fluorescent labelled microsatellites

Five Variable Number of Tandem Repeats Loci (D17S5, APOB, TPO Intron 10, IL-1α Intron 6, and CIAS1) in Thais and Application in the Prenatal Diagnostic Laboratory

Background: Prenatal diagnosis of genetic disease requires DNA analysis of fetal tissue of a responsible gene. Accurate diagnosis is useful for the appropriate management of pregnancy. However, maternal contamination of fetal specimens poses a high preanalytical risk of prenatal misdiagnosis. We have examined five variable number of tandem repeat (VNTR) polymorphisms for use in monitoring potential maternal contamination. Materials and Methods: A study was conducted to examine the heterozygosities of five VNTR loci including, D17S5, APOB, TPO intron 10, IL-1α intron 6, and CIAS1 in 200 unrelated Thai subjects and applied to the monitoring of maternal contamination in 22 families at risk of having fetuses with severe thalassemia. Results: The heterozygosities of D17S5, APOB, TPO intron 10, IL-1α intron 6, and CIAS1 VNTRs were 59.5, 19.5, 66.0, 35.5, and 42.0%, respectively. Therefore, the TPO intron 10 and D17S5 loci were chosen for prenatal diagnosis of thalassemia in 22 families. Analyses of these VNTRs demonstrated an increase of informative data from 59.1% provided by the routine D1S80 VNTR analysis to 90.9%. Conclusions: The VNTR diagnostic procedure described above is simple, cost-effective, rapid, and does not require the use of sophisticated instruments; it should prove useful in the prenatal diagnosis of thalassemia.

Laboratory guidelines for detection, interpretation, and reporting of maternal cell contamination in prenatal analyses a report of the association for molecular pathology

This document summarizes laboratory guidelines for the detection, interpretation, and reporting of maternal cell contamination in prenatal analyses.

Testing for maternal cell contamination in prenatal samples: a comprehensive survey of current diagnostic practices in 35 molecular diagnostic laboratories

The potential presence of maternal cell contamination (MCC) in chorionic villus or amniotic fluid samples poses a serious preanalytical risk for prenatal misdiagnosis. The aim of this study was to identify current diagnostic practices in the absence of comprehensive practice guidelines. Thirty-five clinical molecular laboratories that conduct prenatal testing agreed to participate in a clinical practice survey. The survey included questions about sample requirements, test indications, assay type, test performance and limitations, criteria and management of uninformative test results, reporting, and billing. Sixty percent of participating laboratories performed testing on direct and cultured amniotic fluid, whereas forty percent tested cultured cells only. Most also accepted chorionic villus samples. Although MCC testing of fetal samples is recommended in guidelines by the American College of Medical Genetics, only 60% of surveyed laboratories performed it without exception. Commercially available assays were used by 75% of participating laboratories, and at least five identity markers were evaluated at 87% of the laboratories. The reported lower limit of MCC detection ranged from 1 to 20% but was not determined in all laboratories. MCC testing was performed in the majority of molecular diagnostic laboratories, but guidelines for standardization are needed to ensure optimal and accurate prenatal patient care.

A simple and effective approach for detecting maternal cell contamination in molecular prenatal diagnosis

The presence of maternal cells in fetal samples constitutes a serious potential source for prenatal misdiagnosis. Here we present our approach for detecting maternal cell contamination (MCC) at prenatal diagnosis for eight monogenic disorders (autosomal recessive: beta-thalassaemia, sickle-cell anaemia, cystic fibrosis, prelingual deafness; autosomal dominant: achondroplasia, Huntington disease, myotonic dystrophy, neurofibromatosis type I; X-linked: spinobulbar muscular atrophy). Our aim was to apply a simple and low-cost approach, which would easily and accurately provide information on the fetal tissue MCC status. MCC testing was applied to cases of recessive inheritance where the primary mutation screening of the fetus revealed the presence of the maternal mutation, to cases concerning dominant inheritance and to cases of multiple gestation. The potential presence of maternal cells was determined by the amplification of the 3'-HVR/APO B, D1S80, THO1 and VNTRI of vWf polymorphic loci, which have previously demonstrated high heterozygosity in Caucasians. Among 135 prenatal diagnoses, 44 finally needed to be tested for MCC (32.6%). MCC was detected in four cases, where DNA was isolated directly from chorionic villi samples (CVS), and in one case with DNA isolated directly from amniotic fluid (AF). In almost 90% of cases a simple test of one polymorphic locus provided sufficient information about MCC. The choice of the appropriate locus is therefore essential, while the simultaneous screening of both parents provides the means for distinguishing non-informative sites about MCC.

Developments in laboratory techniques for prenatal diagnosis

Ongoing trends in prenatal diagnosis aim at early, rapid, and ideally noninvasive diagnosis as well as at the improvement of risk-screening for aneuploidy. Interphase-fluorescence in situ hybridization and quantitative fluorescence polymerase chain reaction are efficient tools for the rapid exclusion of selected aneuploidies in addition to the established direct preparation of chromosomes from chorionic villi. Interphase fluorescence in situ hybridization has also made possible the diagnosis of selected chromosome abnormalities in single cells (e.g. in preimplantation genetic diagnosis) or noninvasive diagnosis. More complex multicolor fluorescence in situ hybridization approaches are currently being evaluated. Single cell polymerase chain reaction is the key technique for the molecular diagnosis of a growing number of monogenic conditions before implantation or, still more experimental, in fetal cells retrieved from the maternal circulation. New sources for noninvasive diagnosis came into play such as fetal DNA or cell nuclei in maternal plasma. The combination of biochemical parameters in the maternal serum, namely free beta-human chorionic gonadotropin with pregnancy associated plasma protein A and sonographic markers, has already dramatically increased the sensitivity of risk screening in the first trimester of pregnancy.

Maternal cell contamination of amniotic fluid samples obtained by open needle versus trocar technique of amniocentesis

OBJECTIVE

To determine the incidence of maternal cell contamination (MCC) in the open-needle amniocentesis sampling technique compared with the trocar-in-place technique.

METHODS

A retrospective analysis was conducted on 2,498 mid-trimester amniocenteses performed in two tertiary care centres in Canada. The University of Alberta centre used the open-needle (without the trocar) technique and the University of British Columbia centre used the standard (with the trocar in place) technique. Data were gathered regarding the nature of the amniotic fluid, number of needle passes, amniocentesis results, and the occurrence of maternal cell contamination. The statistical analysis used logistic regression, and controlled for the potential confounders of bloody fluid taps and requirement for more than one needle insertion.

RESULTS

The incidence of maternal cell contamination was 1.16% with the open-needle technique and 0.78% with the standard trocar-in-place technique (p < 0.315), with a power of 42%.

CONCLUSION

The data suggested there is no significant increase in maternal cell contamination with the open-needle versus trocar-in-place techniques of amniocentesis. However, the small sample size, combined with the low prevalence of the outcome of interest (MCC), provides insufficient power to draw firm conclusions about the difference in MCC between the two techniques.

Detection of Y-specific sequences in 122 patients with Turner syndrome: nested PCR is not a reliable method

The incidence of Y chromosome sequences in patients with Turner syndrome has been evaluated in several studies, and its frequency varied from 0% to 61%, depending on the molecular methodology used. The aim of our study was to screen for Y chromosome sequences in 122 patients with Turner syndrome without cytogenetic evidence of this chromosome. DNA of 100 normal women was also screened and it was used as a negative control. To identify cryptic Y mosaicism, eight regions of Y chromosome were amplified by PCR. In order to increase the sensitivity of Y sequence detection, a nested PCR of the SRY and TSPY genes was also performed. All patients had several stigmata of Turner syndrome and none of them presented with signs of virilization. The most frequent karyotype was 45,X (54.1%), followed by mosaicism involving structural aberration of the X chromosome. There were 12 patients who carried a marker or ring chromosome. First-round PCR identified Y chromosome sequences in only four patients (3%), and all of them had a chromosome mosaicism with at least one cell lineage with a marker chromosome. After nested PCR, 25% of the patients and 14% of the normal women were positive for the presence of Y sequences. Contamination with extraneous genomic DNA was ruled out by microsatellite studies, but we cannot eliminate the possibility of contamination with PCR products, despite careful handling. We conclude that nested PCR overestimated the frequency of Y sequences in patients with Turner syndrome and should be avoided to prevent false positive results, which lead to unnecessary surgical treatment of these patients.

Screening practices for mutations in the CFTR gene ABCC7

Cystic fibrosis transmembrane conductance regulator (CFTR) gene studies are now one of the most frequent activities in clinical molecular genetics laboratories. The number of requests is growing, owing to the increasingly wide range of recognized CFTR gene diseases (cystic fibrosis, congenital bilateral absence of the vas deferens, disseminated bronchiectasis, allergic bronchopulmonary aspergillosis and chronic pancreatitis), and the availability of efficient molecular tools for detecting mutations. A growing number of tests capable of simultaneously detecting several frequent CF mutations are being developed, and commercial kits are now available. The most recent kits detect nearly 90% of defective alleles in Caucasians, a rate high enough for carrier screening and for the majority of diagnostic requests. However, because of the wide variety of molecular defects documented in the CFTR gene, only a limited number of laboratories have mastered the entire panoply of necessary techniques, while other laboratories have to refer certain cases to specialized centers with complementary and/or scanning tools at their disposal. A good knowledge of CFTR diseases and their molecular mechanisms, together with expertise in the various techniques, is crucial for interpreting the results. Diagnostic strategies must take into account the indication, the patient's ethnic origin, and the time available in the framework of genetic counseling. This review presents the methods most frequently used for detecting CFTR gene mutations, and discusses the strategies most suited to the different clinical settings.

Detection of hepatitis C virus RNA (HCV RNA) in amniotic fluid: a prospective study

BACKGROUND/AIMS

Mother-to-infant transmission of hepatitis C virus (HCV) has been reported, but the transmission route is unknown. The aim of our study was to detect HCV RNA in amniotic fluid of pregnant women seropositive for HCV.

METHODS

Twenty-two HCV seropositive women were included in the study (median age: 39 years). An amniocentesis was performed in all patients during the 4th month of pregnancy. Sixteen women also tested positive for HCV RNA in serum. The range of HCV RNA titers was 0.3 to 15.1x10(6) Eq/ml (Quantiplex HCV RNA 2.0 Assay, Chiron Diagnostics). Of these 16 viremic patients, four had an anterior placenta, ten had a posterior placenta and the position of the placenta was not determined in two cases. PCR (Amplicor HCV, Roche Diagnostics) was used to detect HCV RNA in the amniotic fluid. We also studied 11 HCV seronegative women as a control group.

RESULTS

In the viremic group (n = 16), HCV RNA was detected once in amniotic fluid. The positive specimen was collected from a patient with an HCV RNA serum value equal to 1.1x10(6) Eq/ml. The placenta was in an anterior position. A PCR inhibitor was detected in one case. No HCV RNA was detected in the amniotic fluid of six seropositive non-viremic patients, nor in the control group. Serum HCV RNA was negative in the ten children tested. The woman whose amniotic fluid contained HCV RNA was the mother of one of them.

CONCLUSIONS

HCV RNA detection in amniotic fluid is rarely positive. The anterior position of the placenta in the only positive detection cannot rule out contamination of the amniotic fluid during the transplacental amniocentesis.

A simple VNTR-PCR method for detecting maternal cell contamination in prenatal diagnosis

The effectiveness of variable number tandem repeats (VNTRs) was evaluated in the detection of maternal cell contamination. Nonradioactive PCRs were performed on 30 sets of prenatal tissue using VNTRs as primers. The combination of two VNTRs (YNZ22 and APOB) provided information on all 30 cases, distinguishing maternal-fetal genotype patterns and detecting maternal cell contamination in 5 of 30 prenatal cases. The amplification of these two VNTRs does not require radioactive or fluorescence labeling, and a small gel electrophoresis is sufficient to see the maternal-fetal genotype pattern. By this method, detection of maternal cell contamination in prenatal tissues can be obtained in 1 day, without the use of expensive instruments, thus providing DNA laboratories a very sensitive, rapid, and simple proof pretest on all prenatal tissues before performing the final genetic diagnostic testing.

Some caveats in PCR-based prenatal diagnosis on direct amniotic fluid versus cultured amniocytes

The polymerase chain reaction (PCR) offers new advances in prenatal genetic diagnosis particularly with limitations in amount of sample, turn-around time of results, and costs. However, maternal contamination is a concern in any fetal sampling, and even more so with PCR given its potential to detect at the level of a few cells. We report our experience with 53 matched pairs of direct and cultured amniocytes using three independent DNA markers amplified by PCR within the setting of a service molecular diagnostic laboratory. Despite 15/53 (30 per cent) of the amniotic fluids showing visible red blood cells prior to culturing, only 5/53 (9 per cent) showed trace PCR contamination. Of note, this was found on only one marker with a particularly robust PCR product of small size and at such a low level that it was unlikely to have resulted in ambiguous interpretation. One of the cultures also showed a similar type of contamination with this same marker. However, in addition, there were 2/53 (3.7 per cent) cultures which showed substantial maternal contamination detected by all three PCR markers, but not visualized on the originating direct samples. Our results suggest that the careful use of direct amniocytes for molecular genetic testing by PCR is reliable and reproducible in most cases.

Transplacental early amniocentesis and pregnancy outcome

The effect on pregnancy outcome of transplacental needle insertion was studied in 401 consecutive women attending for early amniocentesis between 10 and 14 completed weeks of pregnancy. Transplacental early amniocentesis was associated with a significantly higher incidence (P < 0.001) of blood-stained amniotic fluid taps but a lower incidence (not significant; P > 0.05) of pregnancy loss and miscarriages. Women in the nontransplacental early amniocentesis group had a significantly higher (P < 0.01) incidence of late procedure-related antenatal complications, such as preterm rupture of membranes or preterm labour. Our study showed that transplacental early amniocentesis is a safe procedure; contrary to present recommendations, the study also showed that avoiding the placenta during early amniocentesis is an unnecessary practice.