Synergy of Total PLAC4 RNA Concentration and Measurement of the RNA Single-Nucleotide Polymorphism Allelic Ratio for the Noninvasive Prenatal Detection of Trisomy 21

BACKGROUND: Maternal plasma mRNA encoded by the PLAC4 gene (placenta-specific 4), which is transcribed from chromosome 21 in placental cells, is a potential marker for the noninvasive assessment of chromosome 21 dosage in the fetus. We evaluated the diagnostic sensitivities and specificities of 2 trisomy 21-screening approaches that use maternal plasma PLAC4 mRNA. METHODS: We studied maternal plasma samples from 153 pregnant women carrying euploid and trisomy 21 fetuses. For the samples in which the fetuses were heterozygous for the studied PLAC4 single-nucleotide polymorphism (SNP), we measured the ratio between 2 alleles of the SNP in maternal plasma PLAC4 mRNA (RNA-SNP) by mass spectrometric (MS) and digital PCR methods. For pregnancies involving fetuses homozygous for the SNP, we quantified the total PLAC4 mRNA concentration in maternal plasma by real-time PCR and digital PCR. RESULTS: For the RNA-SNP approach, we achieved a diagnostic sensitivity and specificity of 100% (95% CI, 40.2%-100%) and 89.7% (95% Cl, 78.8%-96.1%), respectively, for both the MS and the digital PCR methods. For the mRNA-quantification approach, the areas under the ROC curves were 0.859 (95% Cl, 0.741-0.903) and 0.833 (95% Cl, 0.770-0.923) for plasma PLAC4 mRNA concentrations measured by the real-time PCR and the digital PCR methods, respectively. CONCLUSIONs: For prenatal screening of trisomy 21, the quantification of the total PLAC4 mRNA concentration can be used in a synergistic manner with the RNA-SNP allelic ratio approach to increase the Population coverage of cases in which diagnostic information can be obtained. (C) 2009 American Association for Clinical Chemistry