SHANK3 and autism: DNA methylation was also investigated at the GABA receptor 5 (GABRA5)/GABA receptor 3 (GABRB3) and SHANK3 loci that are located on chromosomes 15q12 and 22q13, respectively. These loci were chosen based on their association with neurodevelopmental disorders such as autism [33–36] and served as negative controls to the significant across-group methylation differences observed on the X chromosome.