ITGB3 and major depressive disorder: Both the candidate gene approach, which has, for many years, been focused on serotonin-related genes, and genome-wide association studies, which have employed SNP arrays, have been disappointing in terms of identifying antidepressant response biomarkers for personalized MDD treatment.30 An alternative approach, that is, genome-wide expression profiling as applied by Morag et al.14 and Oved et al.,17 has led to the identification of two brain-expressed cell adhesion protein-coding genes that are implicated in neurogenesis and synaptogenesis, that is, CHL1 and ITGB3.