DNA序列甲基化是表觀遺傳學調控影響基因表現的一種方式,人類自胚胎發育即有甲基化的改變,出生之後DNA甲基化的變化持續發生,不但在各組織不同,也因年齡不同而有差異。研判檢體來源者年齡及DNA檢體之組織來源為法醫人別鑑定時重要工作。本研究目的是分析DNA甲基化表現,推估DNA檢體來源者年齡,及辨別檢體的體液或組織來源。我們以52個受試者的血液檢體作年齡分析,又以52個受試者血液檢體及24個口腔黏膜檢體作組織來源分析,應用Illumina Human Methylation 450 Beadchip作各基因的甲基化程度分析實驗,分別找出相關的甲基化位點。在年齡鑑別部分,我們找到6個甲基化位置(cg10381440、cg06942183、cg02361903、cg19474833、cg26841048、cg20692569)與年齡分層有明顯相關,可能應用於年齡群估計結果,其年齡層推估之正確率為96.15%;在組織鑑別部分,我們發現以cg02706018、cg03982801、cg07828024、cg19674178這四個點位的甲基化差異,可以正確鑑別血液與口腔黏膜,預測正確率為100%。我們研究找出的基因甲基化標記,可能應用於法醫實務工作中,鑑別現場殘留的人類血液或唾液,及來源者年齡層,引導辦案方向,縮小偵察範圍。
Variation in DNA methylation is one of the epigenetic mechanisms that regulate gene activities. DNA methylations are remodeled since early embryogenesis. It progresses after birth and continues with aging. It varies in different kinds of tissue. The methylations change with age. In forensic casework, it is important to estimate the age of the unknown donor of a forensic sample. It is also helpful to identify the tissue or organ source of a forensic sample, in order to classify the case under investigation. The aim of our study was to find the DNA methylation markers associated with age. We also intended to identify the DNA methylation markers that can classify the tissue origin of the sample. We used blood DNA samples from 52 donors for age stratification analysis. We also used 52 blood DNA samples and 24 oral mucosal DNA samples for tissue origin analysis. The Illumina Human Methylation 450 Beadchip was applied for detection of the level of DNA methylation in different loci. For age stratification, 6 DNA methylation loci (cg10381440, cg06942183, cg02361903, cg19474833, cg26841048, cg20692569) were identified to be useful. The age groups of 96.15% of donors can be predicted with these 6 DNA methylation markers. For tissue origin classification, 4 DNA methylation loci (cg02706018, cg03982801, cg07828024, cg19674178) were noted to be effective to differentiate blood samples from oral mucosal samples. With these 4 DNA methylation markers, 100% of blood and oral mucosal samples can be correctly classified. In conclusion, we identified the DNA methylation markers for age stratification and for discrimination of blood sample from oral mucosal sample. These DNA methylation markers may be helpful to classify the forensic caseworks and to focus the investigation.