Methylation of the imprinted GNAS1 gene in cell-free plasma DNA: equal steady-state quantities of methylated and unmethylated DNA in plasma

Abstract

However, the production and clearance of cell-free DNA from plasma in relation to its methylation status, are poorly understood processes. Methods:We studied the methylation status of DNA derived from the imprinted GNAS1 locus, in cell-free plasma DNA of healthy adults. Heterozygotes were identified that carried the SNP rs1800905 in the imprinted region. The parent-oforigin-dependent DNA methylation was analysed by bisulfite conversion, followed by cloning and sequencing.Results: Genomic DNA molecules derived from both the methylated, maternal, allele and the unmethylated, paternal, allele were found in plasma. Methylated and unmethylated DNA molecules were present in equal numbers. Conclusions:Our data indicate that the methylation status of a DNA sequence has no effect on its steady state concentration in the cell-free DNA component of plasma, in healthy adults.2

Decreased DNA methylation of a CpG site in the HBAP1 gene in plasma DNA from pregnant women

“…This might result in a higher population of the unmethylated second CpG DNA. This phenomenon is contradicted by the study of Puszyk [ 19 ], which suggests that the methylation status of a DNA sequence has no effect on its steady-state concentration in the cell-free DNA component of plasma. Nevertheless, their study focused on the non-pregnant group, while fetal and maternal DNA in our study might have distinct clearance.…”