Objective      To detect the differentially expressed miRNAs in mononuclear cells from Down syndrome (DS) fetal cord blood.       Methods      Solexa high-throughput sequencing technology was conducted to evaluate the miRNA expression in 6 pairs of fetal cord blood mononuclear cells samples from DS fetuses (DS group) and normal fetuses (control group). Stem-loop qRT-PCR was performed to verify the results of Solexa sequencing.       Results      A total of 167 miRNAs were found significantly dysregulated expression in the DS fetal cord blood mononuclear cells compared to the controls. And there were 8 up-regulated miRNAs and 159 down-regulated miRNAs in DS group. Moreover

38 miRNAs and 139 miRNAs were specifically expressed in the DS group and control group

respectively. For the 5 miRNAs encoded by 21 chromosome

with the exception of miR-802

which was up-regulated in DS group

the other 4 Hsa21-derived miRNAs (i.e.

hsa-miR-99a

let-7c

miR-125b

and miR-155) displayed reduced expression.       Conclusion      These results suggested that there is a significant difference between the expression patterns of miRNAs in the DS group and control group

which may be related to the immune deficiency of DS fetus

and the decrease of T/B lymphocytes in DS fetal circulation. The significantly dysregulated and specifically expressed miRNAs are potential prenatal diagnosis biomarkers for DS fetus.