Droplet-Based Digital PCR for Non-Invasive Prenatal Genetic Diagnosis
for Alpha- and Beta-Thalassemia: a feasibility study
Abstract
Objective The aim of this study is to develop ddPCR based-assay for
detecting alpha (0)-thalassemia (SEA) and beta-thalassemia (HbE and
41/42 (-CTTT) from cell-free fetal DNA (cffDNA) extracted form maternal
plasma. Design Feasibility study using sample collected from prenatal
clinic. Setting Thailand. Population 46 couples who were identified to
be carriers of alpha or beta thalassemia. Method Cell-free DNA from 46
singleton pregnant women were isolated and quantified using ddPCR with
specially designed probes for each target allele. Allelic copy number
(CNV) calculation and likelihood ratio test were used to classify the
most likely fetal genotypes. Classification performances were evaluated
against ground truth fetal genotypes obtained from conventional
amniocentesis. Main outcome measures Concordance with fetal genotyping
results from invasive technique. Sensitivity and specificity of
ddPCR-based assays. Results CNV analysis of SEA deletion accurately
classify fetal genotypes in 20 out of 22 cases with an AUC of 0.98 (95%
sensitivity and 91% specificity) for the prediction of Hb Bart’s
hydrops fetalis. Application of sequential probability ratio tests to
detect HbE and 41/42 correctly classified 12 out of 24 cases (10 out of
16 HbE and 2 out of 8 41/42) and provided inconclusive for 7 cases.
Conclusion We showed that ddPCR-based analysis of maternal plasma is an
accurate and effective NIPD for SEA deletion. Although the performance
of ddPCR-based assay on HbE and 41/42 mutations is still not high enough
for clinical application, our work should serve as a good foundation for
future works in this field.