Cell-free fetal RNA from the amniotic fluid supernatant of five euploid mid-trimester samples was divided and prepared in tandem for analysis by either the Affymetrix HG-U133 Plus 2.0 Gene Chip microarray or Illumina HiSeq. Transcriptomes were assembled and compared on the basis of presence of signal, rank-order gene expression, and pathway enrichment using Ingenuity Pathway Analysis (IPA). RNA-Seq data were also examined for evidence of alternative splicing.
Within individual samples, gene expression was strongly correlated (R = 0.43-0.57). Fewer expressed genes were observed using RNA-Seq than gene expression microarrays (4,158 versus 8,842). Most of the top pathways in the “Physiological Systems Development and Function” IPA category were shared between platforms, although RNA-Seq yielded more significant p-values. Using RNA-Seq, examples of known alternative splicing were detected in several genes including H19 and IGF2.
In this pilot study, researchers at Tufts Medical Center found that expression microarrays gave a broader view of overall gene expression, while RNA-Seq demonstrated alternative splicing and specific pathways relevant to the developing fetus. The degraded nature of cell-free fetal RNA presented technical challenges for the RNA-Seq approach.