Abstract
Down's syndrome (DS), a chromosomal abnormal genetic disease caused by a local or total copy of chromosome 21, leads to patients suffering from delayed body growth, special facies, mild to moderate mental retardation and other symptoms, seriously affecting the life of patients. The aim of the present study was to examine the association between Down's syndrome critical region 4 (DSCR4) gene methylation in plasma in high-risk pregnant women with DS in early pregnancy (hereinafter referred to as pregnant women in early pregnancy) and DS, in order to screen new epigenetic markers for the clinical diagnosis of DS. DNA in peripheral blood cells and plasma in pregnant women in early pregnancy were treated with hydrosulphite. DSCR4 genes with different methylation levels were amplified by methylation-specific polymerase chain reaction (PCR), and the methylation difference of the CpG site of the DSCR4 amplification product in peripheral blood DNA was verified via restriction endonuclease analysis. The expression of DSCR4 with different methylation levels in peripheral blood of pregnant women in early pregnancy were detected via reverse transcriptase-quantitative PCR (RT-qPCR), and the DSCR4 gene functions were studied via the intervention in DSCR4 expression with small interfering RNA (siRNA). Methylation-specific PCR and restriction endonuclease analysis revealed that DSCR4 genes were differentially methylated in peripheral blood DNA in pregnant women in early pregnancy. Additionally, DSCR4 showed a low methylation status in plasma but a high methylation status in peripheral blood cells. RT-qPCR revealed that non-methylated DSCR4 was highly expressed in the peripheral blood of pregnant women in early pregnancy, and thus was an epigenetic marker of fetal DS. siRNA results showed that the downregulation of DSCR4 inhibited cell migration and invasion, but had no effect on cell proliferation. The results suggest that the DSCR4 gene was differentially methylated in peripheral blood DNA in pregnant women in early pregnancy. Furthermore, DSCR4 exists in a non-methylated state in plasma and in a hyper-methylated state in blood cells. DSCR4 can therefore promote the migration and invasion of trophocytes and serve as an epigenetic marker of non invasive clinical diagnosis of DS.