Noninvasive prenatal exclusion of haemoglobin Bart's using foetal DNA from maternal plasma

Abstract

Objective: Prenatal diagnosis of alpha-thalassaemia requires invasive testing associated with a risk of miscarriage. Cell-free foetal DNA in maternal plasma presents an alternative source of foetal genetic material for noninvasive prenatal diagnosis. We aimed to exclude HbBart's noninvasively by detection of unaffected paternal alleles in maternal plasma using quantitative fluorescence PCR (QF-PCR).

Method: Microsatellite markers (16PTEL05, 16PTEL06) within the breakpoint regions of -(SEA), -(FIL) and -(THAI) deletions were analysed using QF-PCR of maternal plasma from 30 families. In this blinded study, genotypes were confirmed using conventional PCR. Maternal plasma from two known cases of HbBart's were also analysed.

Results: HbBart's was excluded in 10 out of 30 (33.3%, 95% CI, 17.3-52.8%) mothers by identifying the presence of nondeleted paternally inherited fetal alleles; either only 16PTEL05 (n = 1) or only 16PTEL06 (n = 4), or both (n = 5), and confirmed through direct analysis of fetal DNA. Paternally inherited foetal alleles of 16PTEL05 and 16PTEL06 were not detected in maternal plasma of the two known HbBarts cases. False negatives were excluded with the detection of paternally inherited fetal control marker, D21S1270 in maternal plasma.

Conclusion: We show proof-of-principle that such a test can accurately exclude HbBart's in the foetus by identifying the nondeleted paternally inherited fetal alleles in maternal plasma in one out of three pregnancies, avoiding invasive testing in these pregnancies.