Noninvasive prenatal diagnosis experience in the Çukurova Region of Southern Turkey: detecting paternal mutations of sickle cell anemia and β-thalassemia in cell-free fetal DNA using high-resolution melting analysis

Cord Blood Hematological Parameters of Fetuses Detected Different Thalassemia Genotypes in the Second Trimester of Pregnancy

Background

Hemoglobinopathies are the most common inherited diseases in humans resulting from impaired globin chain synthesis of hemoglobin. The progression of thalassemia rates is prevented with prenatal screening methods.

Aims

To evaluate the hematological parameters of α- and β-thalassemia and normal fetuses aged 17-25 weeks of gestation.

Study Design

A cross-sectional study.

Methods

Pregnant women who underwent cordocentesis in the second trimester because of the risk of having a baby with thalassemia were included in the study. Hematological indices and molecular DNA methods were analyzed from the cord blood samples of 129 women who were 17-25 weeks into pregnancy. The HPLC method was used for Hb fraction analysis. Amplification refractory mutation system, restriction enzyme analysis, multiplex polymerase chain reaction, and sequencing methods were used for the molecular analysis. Maternal contamination was eliminated by the short tandem repeat method.

Results

In total, 112 of the fetuses carry α- and β-thalassemia heterozygous or homozygous (α: 37, β: 58, mixed: 17) and 17 fetuses had a normal genotype for thalassemia. Significant differences in adult hemoglobin (HbA), fetal hemoglobin (HbF), Hb Barts, MCV, MCH, and RDW were detected in three groups compared with the normal group (p < 0.001, except for RBC, Hb, HCT, and MCHC). Differences in HbF, Hb Barts, MCV, MCH, and RDW were observed in the α-thalassemia groups compared with the normal group (p < 0.001). Among the five β-thalassemia subgroups, only HbA and RDW were different from the normal group (p < 0.001).

Conclusion

This study could be a good reference for future studies and prenatal diagnostic applications in emphasizing the importance of changes in the blood parameters of fetuses before molecular genotyping. These hematological data give valuable information to clinicians about the fetus to enlighten families in making appropriate decisions during prenatal diagnosis.

Noninvasive prenatal screening test for compound heterozygous beta thalassemia using an amplification refractory mutation system real-time polymerase chain reaction technique

We propose using a modified amplification refractory mutation system real-time polymerase chain reaction (ARMS RTPCR) technique to exclude the invasive prenatal diagnosis for a non-paternally inherited beta thalassemia mutation in couples atrisk for having a baby with CHBT. The ARMS RT-PCR method was performed for 36 at-risk couples by using isolated fetal cell-free DNA from maternal plasma. The modified ARMS RT-PCR primers targeted one of the following paternally inherited beta thalassemia mutation: -28 A→G, CD17 A→T, CD 26 G→A, IVS1-1 G→T and CD 41-42 -CTTT. The method could be successfully employed for NIPST starting with the 7^th week of gestation. The results showed that 19 pregnant women were negative for PIBTM (53%). After an on-track and on-time of one year, including postnatal thalassemia blood tests, none of the babies showed symptoms or signs of beta thalassemia disease. We concluded that the modified ARMS RT-PCR method was an accurate, cost-effective and feasible method for use as a NIPST for at-risk couples with the potential of having a baby with CHBT.

Optimal non-invasive diagnosis of fetal achondroplasia combining ultrasonography with circulating cell-free fetal DNA analysis

OBJECTIVES

To assess the performance of non-invasive prenatal testing (NIPT) for achondroplasia using high-resolution melting (HRM) analysis, and to propose an optimal diagnostic strategy combining ultrasound examination and cell-free fetal DNA (cffDNA) analysis.

METHODS

In this prospective multicenter study, cffDNA was extracted from blood of pregnant women at risk for fetal achondroplasia (owing to paternal achondroplasia, previous affected child or suspected rhizomelic shortening) and of pregnant low-risk controls. The presence of either one of the two main fibroblast growth factor receptor 3 gene (FGFR3) mutations was determined using HRM combined with confirmation by SNaPshot minisequencing. Results were compared with phenotypes obtained using three-dimensional computed tomography or postnatal examination, and/or molecular diagnosis by an invasive procedure. Fetal biometry (head circumference and femur length) was analyzed in order to develop a strategy in which cffDNA analysis for diagnosis of achondroplasia is offered only in selected cases.

RESULTS

Eighty-six blood samples from women at risk for fetal achondroplasia and 65 from controls were collected. The overall sensitivity and specificity of NIPT were 1.00 (95% CI, 0.87-1.00) and 1.00 (95% CI, 0.96-1.00), respectively. Critical reduction in femur length of affected fetuses could be observed from 26 weeks' gestation.

CONCLUSIONS

HRM combined with SNaPshot minisequencing is a reliable method for NIPT for achondroplasia. Its implementation in routine clinical care combined with ultrasonography is an efficient strategy for the non-invasive diagnosis of achondroplasia. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.

Postnatal and non-invasive prenatal detection of β-thalassemia mutations based on Taqman genotyping assays

The β-thalassemias are genetic disorder caused by more than 200 mutations in the β-globin gene, resulting in a total (β⁰) or partial (β⁺) deficit of the globin chain synthesis. The most frequent Mediterranean mutations for β-thalassemia are: β⁰39, β⁺IVSI-110, β⁺IVSI-6 and β⁰IVSI-1. Several molecular techniques for the detection of point mutations have been developed based on the amplification of the DNA target by polymerase chain reaction (PCR), but they could be labor-intensive and technically demanding. On the contrary, TaqMan^® genotyping assays are a simple, sensitive and versatile method suitable for the single nucleotide polymorphism (SNP) genotyping affecting the human β-globin gene. Four TaqMan^® genotyping assays for the most common β-thalassemia mutations present in the Mediterranean area were designed and validated for the genotype characterization of genomic DNA extracted from 94 subjects comprising 25 healthy donors, 33 healthy carriers and 36 β-thalassemia patients. In addition, 15 specimens at late gestation (21–39 gestational weeks) and 11 at early gestation (5–18 gestational weeks) were collected from pregnant women, and circulating cell-free fetal DNAs were extracted and analyzed with these four genotyping assays. We developed four simple, inexpensive and versatile genotyping assays for the postnatal and prenatal identification of the thalassemia mutations β⁰39, β⁺IVSI-110, β⁺IVSI-6, β⁰IVSI-1. These genotyping assays are able to detect paternally inherited point mutations in the fetus and could be efficiently employed for non-invasive prenatal diagnosis of β-globin gene mutations, starting from the 9^th gestational week.

First trimester fetal aortic Doppler for hemoglobinopathies

Objective:

To evaluate fetal aortic Doppler for the prenatal diagnosis of hemoglobinopathies in the first trimester of pregnancy.

Materials and Methods:

Between January and November 2014, a total of 108 patients were enrolled in the study. The couples were carriers of either alpha/beta thalassemia, sickle cell disease or combined carriers of these and were admitted to Çukurova University Faculty of Medicine, Department of Obstetrics and Gynecology Prenatal Diagnosis Center. One hour before the chorionic villus sampling (CVS), patients were evaluated using fetal aortic Doppler. Pulsatility index, peak systolic velocity, and heart rate were noted.

Results:

There were no statistically significant differences in Doppler indices between different groups of CVS results when compared with the healthy controls.

Conclusion:

Fetal aortic Doppler investigation was found to be ineffective for the prenatal diagnosis of hemoglobinopathies.

High-resolution melting analysis for noninvasive prenatal diagnosis of IVS-II-I (G-A) fetal DNA in minor beta-thalassemia mothers

OBJECTIVES

The high-resolution melting (HRM) technique is fast, effective and successful method for mutation detection. The aim of this study was to determine the sensitivity and specificity of the HRM method for detection of a paternally inherited mutation in a fetus as a noninvasive prenatal diagnosis of β-thalassemia.

METHODS

Genomic DNAs were prepared from 50 β-thalassemia minor couples whose pregnancy was at risk for homozygous β-thalassemia. Ten milliliters of the maternal blood from each pregnant woman were collected and after separating plasma stored at -80 °C until analysis. The extracted DNAs were analyzed by HRM real-time PCR for detection of IVS-II-I (G-A) as a paternally inherited mutation. The gold standard was the result of a chorionic villus sampling by a standard reverse dot blotting test.

RESULTS

The sensitivity and specificity of HRM real-time PCR were 92.6% and 82.6%, respectively. Also, the positive and negative predictive values were 86.2% and 90.47%, respectively.

CONCLUSIONS

HRM real-time PCR was a sensitive and specific method for determining the paternally inherited mutation in the fetus at risk with thalassemia major.

Evaluation of suitable control genes for quantitative polymerase chain reaction analysis of maternal plasma cell-free DNA

The content stability of commonly used control genes is considered to vary significantly in different independent experimental systems, either in the expression of RNA expression or in the level of DNA content. The present study aimed to examine a panel of six common control genes, including β‑globin (HBB), telomerase (TERT), glyceraldehyde‑3‑phosphate dehydrogenase (GAPDH), albumin (ALB), β‑actin (ACTB) and T cell receptor γ (TRG), in order to evaluate and validate the most reliable control genes for quantitative polymerase chain reaction (qPCR) in investigations for the analysis of fetal‑derived DNA and maternal‑derived DNA in maternal plasma to enable non‑invasive prenatal assessment. Plasma DNA was extracted from the peripheral blood of 20 pregnant femals (gestational age, 18.67 ± 0.58 weeks) using a QIAamp DNA mini kit. Electrophoresis was performed to separate the fetal‑derived DNA and the maternal‑derived DNA at the 300bp position. qPCR was then performed, followed by geNorm‑, NormFinder‑ and BestKeeper‑based analyses to evaluated the content stabilities of the six candidate control genes in the fetal‑derived DNA and maternal‑derived DNA. The subsequent analysis of the experimental data revealed that HBB was expressed in the maternal‑ and fetal‑derived DNA together and in the maternal‑derived DNA alone. In addition, GAPDH in the fetal‑derived DNA enabled efficient normalization for qPCR investigations in the maternal plasma DNA.