This large cohort study shows significant, although modest, associations between MDD and specific hypothalamic-pituitary-adrenal axis indicators. Because a higher cortisol awakening response was observed among both subjects with current MDD and subjects with remitted MDD, this may be indicative of an increased biological vulnerability for depression.

No abstract

Data from the Genetic Association Information Network (GAIN) genome-wide association study (GWAS) in major depressive disorder (MDD) were used to explore previously reported candidate gene and single-nucleotide polymorphism (SNP) associations in MDD. A systematic literature search of candidate genes associated with MDD in case-control studies was performed before the results of the GAIN MDD study became available. Measured and imputed candidate SNPs and genes were tested in the GAIN MDD study encompassing 1738 cases and 1802 controls. Imputation was used to increase the number of SNPs from the GWAS and to improve coverage of SNPs in the candidate genes selected. Tests were carried out for individual SNPs and the entire gene using different statistical approaches, with permutation analysis as the final arbiter. In all, 78 papers reporting on 57 genes were identified, from which 92 SNPs could be mapped. In the GAIN MDD study, two SNPs were associated with MDD: C5orf20 (rs12520799; P = 0.038; odds ratio (OR) AT = 1.10, 95% CI 0.95-1.29; OR TT = 1.21, 95% confidence interval (CI) 1.01-1.47) and NPY (rs16139; P = 0.034; OR C allele = 0.73, 95% CI 0.55-0.97), constituting a direct replication of previously identified SNPs. At the gene level, TNF (rs76917; OR T = 1.35, 95% CI 1.13-1.63; P = 0.0034) was identified as the only gene for which the association with MDD remained significant after correction for multiple testing. For SLC6A2 (norepinephrine transporter (NET)) significantly more SNPs (19 out of 100; P = 0.039) than expected were associated while accounting for the linkage disequilibrium (LD) structure. Thus, we found support for involvement in MDD for only four genes. However, given the number of candidate SNPs and genes that were tested, even these significant may well be false positives. The poor replication may point to publication bias and false-positive findings in previous candidate gene studies, and may also be related to heterogeneity of the MDD phenotype as well as contextual genetic or environmental factors.

Although we have previously shown that the integrity of inflammatory mediator-induced activation of the hypothalamic-pituitary-adrenal axis is essential for conferring resistance to inflammatory disease in susceptible Lewis rats, the role of endogenous glucocorticoid secretion in human immune function in either health or disease is less clear. To further understand the relevance of physiological variations in plasma cortisol on immune function in humans, we evaluated ex vivo lipopolysaccharide-induced interleukin-1 beta (IL-1 beta), IL-6, and tumor necrosis factor-alpha (TNF alpha) production in the whole blood of healthy volunteers studied under conditions chosen to approximate either physiological or pharmacological glucocorticoid levels. Administration of a pharmacological dose of hydrocortisone suppressed the production of all three cytokines, whereas administration of a physiological dose of hydrocortisone suppressed only TNF alpha production. Stress-induced levels of glucocorticoids, achieved during exercise at 100% maximal oxygen utilization, suppressed IL-1 beta and TNF alpha production, but were without effect on IL-6 production. In addition, circadian variations of cortisol were associated with decreased TNF alpha production, but were without effect on IL-1 beta or IL-6 production. These studies challenge the generally accepted idea that glucocorticoids consistently suppress cytokine production and indicate a hierarchy of sensitivity, with TNF alpha having the greatest sensitivity, IL-1 beta having intermediate sensitivity, and IL-6 being resistant. The resistance of IL-6 production to glucocorticoid suppression is compatible with data suggesting an antiinflammatory as well as a proinflammatory action for this cytokine.

This study showed a modest but significantly higher 1-hour cortisol awakening response among anxiety patients, which was driven by those with panic disorder with agoraphobia and those with comorbid depression.