Noninvasive prenatal diagnosis for pregnancies at risk for β‐thalassaemia: a retrospective study

Abstract

Objective To evaluate the clinical feasibility of noninvasive prenatal diagnosis (NIPD) for b-thalassaemia using circulating single molecule amplification and re-sequencing technology (cSMART). Design zThrough carrier screening, 102 pregnant Chinese couples carrying pathogenic HBB gene variants were recruited to the study. Pregnancies were managed using traditional invasive prenatal diagnosis (IPD). Retrospectively, we evaluated the archived pregnancy plasma DNA by NIPD to evaluate the performance of our cSMART assay for fetal genotyping. Setting Chinese prenatal diagnostic centres specialising in thalassaemia testing. Population Chinese carrier couples at high genetic risk for bthalassaemia. Methods Fetal cell sampling was performed by amniocentesis and HBB genotypes were determined by reverse dot blot. NIPD was performed by a newly designed HBB cSMART assay and fetal genotypes were called by measuring the allelic ratios in the maternal cell-free DNA. Main outcome measures Concordance of HBB fetal genotyping between IPD and NIPD and the sensitivity and specificity of NIPD. Results Invasive prenatal diagnosis identified 29 affected homozygotes or compound heterozygotes, 54 heterozygotes and 19 normal homozygotes. Compared with IPD results, 99 of 102 fetuses (97%) were correctly genotyped by our NIPD assay. Two of three discordant samples were false positives and the other sample involved an incorrect call of a heterozygote carrier as a homozygote normal. Overall, the sensitivity and specificity of our NIPD assay was 100% (95% CI 88.06-100.00%) and 97.26% (95% CI 90.45-99.67%), respectively. Conclusions This study demonstrates that our cSMART-based NIPD assay for b-thalassaemia has potential clinical utility as an alternative to IPD for pregnant HBB carrier couples.

Noninvasive Detection of Fetal Genetic Variations through Polymorphic Sites Sequencing of Maternal Plasma DNA

“…Here, we estimated the genotype of each target site using the sample’s fetal fraction and read counts of mutant and wildtype alleles which were the only information required by our allelic goodness of fit method, and then compared the estimated genotype with the true genotype reported. Using allelic counts of a single target site, 100% estimation accuracy was observed for all maternal genotypes, and 95.7%, 93.4% and 96.8% for fetal genotypes of the hbb dataset 12 , the arnshl dataset 13 and the cfbest dataset 14 , respectively (Table 1; Table S9-S12). Moreover, when both the mother and the fetus were homozygous wildtype, 100% accuracy was observed (Table S9-S12).…”

“…The wilson validation dataset was retrieved from Supplementary Table 4 11 and the wilson disease dataset from Table 2 11 . The hbb dataset was retrieved from Table S1 12 , the arnshl dataset from Supplementary Table S2 13 and the cfbest dataset was retrieved from Table S8 14 . The simulated datasets were generated using ART 15 simulator.…”

Reply

“…However, for the time being, these techniques examining cell-free DNA in maternal blood are used for screening (and not diagnosis) for aneuploidy, with a very high detection rate for trisomy 21 but being less effective for other trisomies 5 . Regarding hemoglobinopathy, diagnosis is often difficult or even incorrect with a false-positive or false-negative result, and further improvements are needed before they can be used in clinical practice, especially when both parents carry the same trait 6,7 . Additionally, these techniques are generally applied beyond 10 weeks of gestation and, therefore, any possibility of intrauterine treatment is lost.…”

Differential diagnosis of thalassemia and iron deficiency anemia in pregnant women using new formulas from multidimensional analysis of red blood cells

“…Thalassemia is a common monogenic disease caused by defects in the synthesis of hemoglobin chains (3), and is highly prevalent in the tropics and subtropics (4). In China, the incidence rate of thalassemia mutations along the coastal areas of southern China is higher than that in inland regions (3,5). Therefore, in Guangdong Province, the identification of thalassemia carriers is important in premarital counselling to prevent the inheritance of severe and potentially lethal forms of thalassemia (6).…”