COBRA of the subtelomeres specific for chromosome 17p in healthy Japanese. Bisulfite-treated genomic DNA of the participants was polymerase chain reaction–amplified with chromosome arm–specific primers and digested with MspI. Ladder of HaeI-digested φX174 DNA is shown in the left of the each gel. A complete digestion of the amplified bisulfite-untreated product with MspI yields the bands, which are indicated by black arrowheads. The age, TRF, and relative subtelomeric methylation rate are shown on the top of each panel. Note that 6 of the 30 participants (2 in their 20s, 1 in the 40s, and 3 in the 60s) represent extra bands indicated by white arrowheads, which contain thymine residue changed from unmethylated cytosine residue by the bisulfite treatment. Almost all participants, except for those with extra bands, seem to show the subtelomeric region on chromosome 17p to be well methylated. COBRA = combined bisulfite restriction analysis; TRF = terminal restriction fragment.