目的　通过检测免疫性血小板减少症(ITP)患儿外周血淋巴细胞中DNA甲基转移酶1(Dnmt1)、DNA甲基转移酶3a(Dnmt3a)mRNA的表达，探讨DNA甲基化与儿童ITP发病机制之间的联系。方法　采用RT-PCR方法检测36例新诊断ITP患儿与26例健康体检儿童外周血淋巴细胞中Dnmt1、Dnmt3a mRNA的表达水平；并进行分析比较。结果　新诊断ITP患儿外周血淋巴细胞中Dnmt1的mRNA表达为(3.02±0.49)，较对照组(4.58±0.52)明显降低，差异有统计学意义(t=11.95，P<0.01)；ITP患儿Dnmt3a mRNA的表达为(1.49±0.44)，较对照组(2.41±0.32)明显降低，差异有统计学意义(t=9.12，P<0.01)。结论　新诊断ITP患儿可能存在DNA低甲基化，这种DNA低甲基化与儿童ITP发病机制关系密切。

Objective　To study the relationship between DNA methylation and pathogenesis of childhood immune thrombocytopenic purpura (ITP) by examining the expression of DNA methyltransferase 1(Dnmt1) and DNA methyltransferase 3a (Dnmt3a) mRNA in peripheral blood lymphocytes of the children with ITP. Methods Expression of Dnmt 1 and Dnmt3a mRNA in the peripheral blood lymphocytes in 36 children with newly diagnosed ITP and 26 healthy children were detected using RT-PCR. Results Dnmt1 mRNA expression in peripheral blood lymphocytes in children diagnosed with ITP was 3.02±0.49, significantly lower than 4.58±0.52 in the control group (t=11.95, p<0.001). Dnmt3a mRNA expression in peripheral blood lymphocytes in children diagnosed with ITP was 1.49±0.44, significantly lower than 2.41±0.32 in the control group (t=9.12, p<0.001). Conclusions Children with newly diagnosed ITP have lower DNA methylation status in peripheral blood lymphocytes as compared to that in healthy children. The DNA methylation may play an important role in the etiology of acute ITP in children.