GABRD and anxiety disorder: Furthermore, differential methylation has been identified at CpGs mapping to the GABA Type B Receptor Subunit 2 (GABBR2) and GABA Receptor Subunit Delta (GABRD) belonging to the gamma-aminobutyric acid (GABA) system, which is known to be centrally involved in the pathogenesis of fear, anxiety and anxiety disorders [60–62].