GAD1 and schizophrenia: Levels of GAD1 DNA methylation in open chromatin (H3K4me3) were strikingly similar between schizophrenia subjects and controls, with extremely low levels at the promoter (<0.5%) (Fig. 2A lower panel, and Fig. 2B) and a higher methylation frequency (approximately 15%) within intron 2 (Fig. 2A lower panel, and Fig. 2C).