Abstract
Concentrations and expression profile of extracellular chromosome 21-derived microRNAs (miR-99a, let-7c, miR-125b-2, miR-155 and miR-802) were studied with the aim to distinguish between pregnancies bearing euploid fetuses and those affected with Down syndrome. RNA enriched for small RNAs was isolated from plasma samples of 12 Down syndrome pregnancies, 12 women with normal course of gestation and 10 non-pregnant individuals.
MicroRNA transcribed into cDNA using specific stem-loop primer was detected using real-time PCR assay. Simulation experiments using RNA pools of healthy non-pregnant individuals and aneuploid amniotic fluid samples in descending dilution ratio ranging from 1:1 to 1000:1 were used to test the detection limit of the technique for over-expressed chromosome 21-derived microRNAs specific for Down syndrome. 4 out of 5 extracellular chromosome 21-derived microRNAs (miR-99a, let-7c, miR-125b-2 and miR-155) were reliably detected in plasma samples.
Simulation experiments revealed the detection limit of aneuploidy at a ratio 100:1 for let-7c, miR-125b-2 and miR-155, and a ratio of 1000:1 for miR-99a. Overexpression of extracellular miR-99a, miR-125b-2 and miR-155 was observed in pregnant women compared to non-pregnant individuals.
Similarly, increased concentrations of extracellular miR-99a and miR-125b-2 were detected in pregnant women than in non-pregnant individuals. Unfortunately, the concentrations and relative gene expression of extracellular chromosome 21-derived microRNAs did not differ between the cohorts of pregnancies bearing euploid fetuses and those affected with Down syndrome.
Analysis of extracellular chromosome 21-derived microRNAs has no benefit for screening programs and non-invasive diagnosis of Down syndrome.