Supplementary Material for: Molecular and Genetic Characterization of Depression: Overlap with Other Psychiatric Disorders and Aging

Genome-wide expression and genotyping technologies have uncovered the genetic bases of complex diseases at unprecedented rates. However, despite its heavy burden and high prevalence, the molecular characterization of major depressive disorder (MDD) has lagged behind. Transcriptome studies report multiple brain disturbances but are limited by small sample sizes. Genome-wide association studies (GWAS) report weak results but suggest an overlapping genetic risk with other neuropsychiatric disorders. We performed a systematic molecular characterization of altered brain function in MDD using meta-analysis of differential expression of 8 gene array studies across 3 corticolimbic brain regions in 101 subjects. The identified ‘metaA-MDD' genes suggest altered neurotrophic support, brain plasticity and neuronal signaling in MDD. Notably, metaA-MDD genes display a low connectivity and hubness in coexpression networks as well as a uniform genomic distribution, which is consistent with diffuse polygenic mechanisms. We have integrated these findings with results from over 1,800 published GWAS and show that genetic variations nearby metaA-MDD genes predict a greater risk for neuropsychiatric disorders, and notably for age-related phenotypes, but not for other medical illnesses (including those frequently co-occurring with depression) or body characteristics. Collectively, the intersection of unbiased investigations of gene function (transcriptome) and structure (GWAS) provides novel leads to investigate molecular mechanisms of MDD and suggests common biological pathways between depression, other neuropsychiatric diseases and brain aging.