Evaluation of: Lo YM, Tsui NB, Chiu RW et al. Plasma placental RNA allelic ratio permits noninvasive prenatal chromosomal aneuploidy detection. Nat. Med. 13, 218–223 (2007).

A recent report by Dennis Lo and colleagues has indicated that the analysis of placentally derived cell-free mRNA can be used to detect fetal Down syndrome. The unique aspect of this work is that fetal ploidy for chromosome 21 was determined by a quantitative assessment of gene expression for a chromosome 21-specific gene, namely PLAC4. This technical feat was achieved by quantifying the relative expression of PLAC4 alleles to each other by the mass spectrometric analysis of single nucleotide polymorphism loci. By these means, fetal trisomy 21 could be detected noninvasively with a sensitivity of 90% for a false-positive rate of less than 3.5%. Hence, it is highly probable that this salient development could usher in a new era in noninvasive prenatal diagnosis.