利用RASSF1A位点检测母体血浆中胎儿SNP分型

目的探讨利用母体血浆中高甲基化RASSF1A位点进行胎儿SNP分型的应用价值。方法随机收集10个未孕健康妇女和45例不同孕期（早期5例、中期20例、晚期20例）孕妇的血样本及相应胎儿组织（绒毛组织、羊水、胎盘组织）;利用甲基化敏感限制性内切酶BstUI酶切后进行PCR,产物进行血细胞、血浆和胎儿组织（绒毛或胎盘）DNA RASSF1A序列的甲基化模式检测,并采用直接测序法对SNP rs4688725位点进行分型。结果经BstUI酶消化,RASSF1A序列在母体血细胞中均未检出,而在绒毛或胎盘组织中均能检出;在45名孕妇血浆中,RASSF1A序列均能被检出,且序列内的SNP分型与相应胎儿组织一致;在10名非孕妇女血浆中均未检出RASSF1A序列。结论母体和胎儿DNA中RASSF1A基因启动子区域的甲基化模式存在差异,可用于对母体血浆中的游离胎儿DNA进行SNP分型。

Research of detecting and typing fetal SNP in maternal plasma using RASSF1A

Objective To discuss the application value of hypermethylated RASSF1A sequences in matern＇al blood for fetal SNP genotyping. Methods Blood samples and fetal tissues from 10 non-pregnant healthy Women and 45 pregnant women with different gestational ages （5 in the 1 st-trimester, 20 in the 2nd-trimester and 20 in the 3rd-trimester） were collected randomly. Using conventional PCR ~ter digestion with BstUI, a methylation-sensitive restriction enzyme （ MSRE-PCR）, to detect the methylation pattern of RASSF1A sequences in maternal blood cells, fetal tissues （ CVS or placenta） and maternal plasma DNA. Detect sequencing were employed to perform SNP rs4688725 genotyping. Results The amplified RASSF1A sequence was found to be hypermethylated in CVS or placental tissues and hypomethylated in maternal blood cells. Hypermethylated RASSF1A sequences were detectable in the plasma of all 45 pregnant women while absent in the 10 nonpregnant women. The genotype of plasma RASSF1A after enzyme digestion was identical to the fetal genotype in each case. Conclusion Since the promoter of RASSF1A gene has been reported to be hypermethylated in fetal placental tissue while hypomethylated in the maternal blood cells, it was used for SNP typing of fetal DNA in maternal plasma. This study demonstrated the potential utility of specific fetal epigenetic marker containing informative SNP in maternal plasma for noninvasive fetal SNP genotyping in pregnancy.