Patterns of DNA methylation are indistinguishable in different individuals over a wide range of human DNA sequences.

Patterns of DNA methylation at 5'-CCGG-3' and 5'-GCGC-3' sequences were determined in about 570 kb, equivalent to about 0.02% of the human genome, by using HpaII and HhaI restriction endonucleases, respectively, and randomly selected cosmid clones of human DNA as hybridization probes. Many of these human DNA sequences were of the repetitive type. The DNAs from human lymphocytes, from a mixture of all blood cells or from several established human cell lines (HeLa, KB, 293, or DEV) were included in these analyses. In the segments of the human genome investigated, the patterns of DNA methylation were characterized by often completely or partly methylated 5'-CCGG-3' or by partly methylated 5'-GCGC-3' sequences. Even among individuals of different genetic origins (East-Asian or Caucasian), these patterns of DNA methylation proved indistinguishable by the method applied. The cytokine-dependent stimulation of human lymphocytes to replicate in culture did not affect the stability of these patterns. In the same DNA sequences from several human cell lines, much lower levels of DNA methylation were observed. In human cell lines some of the investigated sequences were unmethylated. The results presented lend credence to the notion that the human genome exhibits highly cell type-specific patterns of DNA methylation which are often indistinguishable among different individuals even of different genetic backgrounds.