A Research Of 21q CpG Islands DNA Methylation Status In Trisomy 21

Background: Trisomy 21 is a chromosomal condition caused by the presence of all or part of an extra 21st chromosome. Often Trisomy 21 is associated with some impairment of cognitive ability and physical growth, and is one of the high incidence birth defect. Individuals with Trisomy 21 are incurable, so prenatal screens for Trisomy 21 are likely lead to reductions in overall social welfare burden. Although some scientists reported a few epigenetic markers for the prenatal screen of Trisomy 21, there is still short of the research about the DNA methylation status of CpG islands in 21q. Therefore exploring the DNA methylation status of CpG islands in 21q is essential for developing a series of specific and effective epigenetic marker for the prenatal screen of Trisomy 21.Method: First DNA sequences of CpG islands in 21q from USCS database were achieved, and 149 sequences and 148 pairs of primers in BGI YH database were aligned. Then the HM-PCR assay was improved, to determine the DNA methylation status of CpG islands in patients with Trisomy 21. Finally there were totally 2690 CpG island analyzed by HM-PCR assay, and a comparison of the DNA methylation status of CpG islands were made between the control and patients with Trisomy 21Results: According to the results of alignment in BGI YH database, 149 DNA sequences of CpG islands in 21q and 148 pairs of primers for 148 CpG islands are feasible to be used in HM-PCR. HM-PCR assay developed by Yamada were further improved to a simple assay by optimizing experimental condition. Using the improved HM-PCR assay, the results showed that there was no difference in the DNA methylation status of 21q CpG islands between patients with Trisomy 21 and the control. Totally 148 CpG islands in 21q were screened, including 98 null methylation, 30 complete methylation, 12 composite methylation and 8 incomplete methylation. However, 4 null methylation CpG islands (No. 11, 15, 27, 71) and 1complete methylation (No.93) in Japanese were composite methylation in Chinese. The 5 CpG islands were different in DNA methylation level between Japanese and Chinese. Whether the difference is due to the race difference or not, the bisulfite sequencing will be used to detect the DNA methylation status of the 5 CpG islands. Another one CpG island (No.103) will be detected by bisulfite sequencing, because the DNA sequence is no HpaII and HhaI recognition site.Conclusion: There is no difference in the DNA methylation status of 21q CpG islands between patients with Trisomy 21 and the control. The hypothesis that the homogeneity of DNA methylation status of 21q CpG islands in Chinese indicates that DNA methylation is a epigenetic marker to distinguish the different race, is need to be verified by bisulfite sequencing to detect the DNA methylation status.