GAD1 and neoplasm: Interestingly, in brain metastatic tumor cells, it was reported that the downregulation of the DNA methyltransferase DNMT1 induced by the brain microenvironment‐derived clusterin resulted in decreased GAD1 promoter methylation and subsequent upregulation of GAD1 expression.21 Therefore, even the effect of methylation levels of CpG sites around GAD1 on its expression level may vary under different conditions or in different cell lineages.