Figure 1

DNA methylation difference between twins in SLC6A4. (a) Results of comprehensive DNA methylation analysis of lymphoblastoid cell lines (LCLs) of a pair of monozygotic twins discordant for bipolar disorder using tiling arrays. The vertical axis represents the signal intensity, and the horizontal axis represents the base number on the chromosome 17 (NCBI36/hg18). Exon–intron structure of the SLC6A4 is shown below the data of tiling arrays. The CpG island and the regions of HTTLPR are shown by a green square and an arrow, respectively. The region showing statistically significant methylation difference between the bipolar twin and the healthy co-twin, and the region examined by bisulfate sequencing are shown by a blue square and a red bar, respectively. (b) Results of bisulfite sequencing. The genomic region examined by bisulfite sequencing, which corresponds to the base numbers from 25 586 333 and 25 586 482, is shown above. The five CpG sites are surrounded by red squares. Black and white circles represent the methylated and unmethylated CpGs, respectively. Each raw shows the data of one clone. Five circles in one raw represent the five CpG sites shown above. This region is methylated in the bipolar twin but not in the healthy co-twin. (c) Representative results of pyrosequencing using independent samples. The results of two CpG sites (3 and 4) were shown by yellow shadows. Percentages of C and T mean fractions of methylation and unmethylation on each CpG site, respectively. Each fraction of methylation on other CpG sites of the bipolar twin and the healthy co-twin was 24.2 and 0 on CpG1, 28.8 and 0 on CpG2, and 9.3 and 4.3 on CpG5, respectively. The differences of DNA methylation in SLC6A4 between the twins were confirmed using the other LCL samples of the twins recultured for this experiment.