Maternal plasma bisulfite DNA sequencing: tomorrow starts today.

The report in this issue of Clinical Chemistry by Lun, Chiu, and coworkers of the Centre for Research into Circulating Fetal Nucleic Acids at the Chinese University of Hong Kong is an excellent example of this process (2 ). The investigators used genomewide bisulfite DNA sequencing of maternal plasma to comprehensively assess the epigenomic profiles of both fetal and maternal epigenomes noninvasively, serially, and on a genomewide scale. As a proof of principle, the authors correctly detected trisomy 21 by assessing the methylation density of chromosome 21 and correctly deduced the imprinting status of 4 selected loci: H19 [H19, imprinted maternally expressed transcript (non-protein coding)], KCNQ1OT1 [KCNQ1 opposite strand/antisense transcript 1 (non-protein coding)], MEST (mesoderm specific transcript), and GNAS (GNAS complex locus).