中文摘要：

目的 分析母血中非性别依赖的胎儿表观遗传学标记超甲基化Ras相关区域家族1A（Ras association domain family 1A,RASSF1A）基因的检测效率,探讨其替代SRY基因检测游离胎儿DNA的可行性. 方法 选择2011年5月1日至2012年4月30日于山西省大同市第一和第五人民医院进行产前检查的正常妊娠妇女50例,分别于妊娠早、中、晚期采集外周静脉血,胎儿出生后确定为男胎的孕妇（28例）为研究对象.选择20例同期体检的健康未妊娠女性作为阴性对照.通过甲基化敏感的限制性内切酶消除母源性（非甲基化）RASSF1A基因,采用TaqMan实时荧光定量聚合酶链反应检测胎源性（超甲基化）RASSF1A基因,同时测定孕妇血浆中SRY基因并作为参照,对检测结果进行相关性分析.统计学方法采用Shapiro-wilk分析、Pearson或Spearman秩相关分析和x2检验. 结果 28例男胎孕妇共进行84次检测,超甲基化RASSF1A基因最早于妊娠第8＋2周检出,检出率97.62％（82/84）.对照组未检测到超甲基化RASSF1A基因和SRY基因.妊娠早、中、晚期孕妇血浆中酶切后RASSF1A基因及SRY基因的含量分别为（60.19±14.16） copies/ml与（58.22±15.13） copies/ml（r=0.933,P＜0.01）、（99.18±28.44） copies/ml与（95.43±32.33） copies/ml（r=0.931,P＜0.01）、（144.93±33.51） copies/ml与（132.96±28.24） copies/ml（r=0.654,P＜0.01）.酶切后RASSF1A和SRY基因含量均与孕周呈正相关（r分别为0.933和0.896,P均＜0.01）. 结论 检测表观遗传学标记超甲基化RASSF1A基因所得的游离胎儿DNA结果与SRY基因具有较高的一致性,该基因突破了胎儿性别的局限,有助于扩大无创伤性产前诊断的临床应用范围.

英文摘要：

Objective To analyze the detection efficiency of non-sex dependent Ras association domain family IA （ RASSF1A ） sequences in maternal plasma as a fetal epigenetic marker, and to explore the feasibility of replacing SRY gene in quantitative detection of fetal free DNA. Methods Maternal peripheral blood samples were collected in the first, second and third trimester from 50 normal pregnant women who had their prenatal care in the First and Fifth People＇s Hospital in Datong, Shanxi Province, between May 1, 2011 and April 30, 2012. Among them, pregnant women with single male fetus （ n=28 ） were selected as study group, and another 20 normal healthy non-pregnant women in the same period were selected as control. The methylation- sensitive restriction enzymes were used specifically to cut the maternal hypomethylated RASSF1A gene, the fetal hypermethylated sequences were determined by fluorescence quantitative polymerase chain reaction, and SRY sequences in maternal plasma were determined as a reference. Shapiro-wilk, Pearson or Spearman correlation analysis and Chi square test were applied for statistical analysis. Results Among the 28 pregnant women with male fetus, the hypermethylated RASSFIA sequences in maternal plasma was tested 84 times and identified as early as at 8＋z weeks of gestation, giving the detection rate of 97.62% （ 82/84 ） . However, no RASSF1A or SRY gene was identified in control group. The mean concentrations of hypermethylated RASSF1A and SRY gene in the first, second and third trimester group were （ 60.19± 14.16 ） copies/ml vs （ 58.22±15.13 ） copies/ml （ r=0.933, P〈0.01 ） , （ 99.18±28.44 ） copies/ml vs （ 95.43±32.33 ） copies/ml （ r=0.931, P〈0,01 ） and （ 144.93±33.51 ） copies/ml vs （ 132.96±28.24 ） copies/ml （r=0.654, P〈0.01 ） , respectively. The mean concentrations of hypermethylated IdSSFJA and SRY gene showed positive correlation with gestational weeks （ r=0.933 and 0.896, P〈0.01, respectively ） . Coneluslons By using hyperm