OXTR and major depressive disorder: For OXTR, three genomic regions were investigated: (i) a region within intron 1 that has previously been associated with autism symptoms and both externalizing and internalizing behaviors [32,34,35]; (ii) the promoter region upstream of the start codon, which plays a crucial role in the control of OXTR transcription [35]; and (iii) a region within exon 3 that has been associated with various psychopathologies, including anxiety and depression, obsessive–compulsive disorder, post-traumatic stress disorder, and deficits in social communication [36,37].