With respect to the question of where to measure, studies about epigenetic modification in the etiology of psychiatric diseases have measured markers of epigenetic modification in several tissues, including peripheral blood cells,[46] other peripheral tissues (such as buccal mucosal cells),[47] and post-mortem brain cells.[48] While all nucleated human cells host the full complement of genetic material, different cells may alter gene expression differently to best accomplish their particular function throughout the course of specialization, activating some genes while silencing others in line with physiologic roles.[10,11] Although the pathophysiology of psychiatric disease remains largely unclear, it is known that psychiatric pathology—the cellular changes that mechanize disease phenotypes—is localized somewhere in the brain.[49] For this reason, measuring epigenetic modification in peripheral tissues, like peripheral blood cells or buccal mucosa without evidence that these peripheral changes are pathognomonic and specific is problematic.
