Predisposed to Depression?

Depression, primarily major depressive disorder (MDD), is the leading cause of disability in adults.  MDD is primarily familial, prompting research to the nature-nurture origins of the disease.  How is depression tied genetically or shaped by environmental factors in individuals?

The exact mechanisms by which depression affects the brain are fairly unknown.    We know there are brain abnormalities and differences, but some studies have shown it to be hard to discern if the brain differences were causes or effects of depression.

Peterson et al looked at a three generation cohort of individuals, assessing those with and without major depressive disorder in two successive generations.  The results of their research appear in last week's Proceedings of the National Academy of Sciences issue (epub ahead of print).  Peterson et al, found that people at risk for depression (those with a family history in 2 generations) had 28% more cortical thinning in the right hemisphere of their brains than those not at risk for depression.  The thinning occured in gray matter, the core processing brain center (the neurons) as opposed to in white matter, information transport system (the myelinated axons).  28% is a significant amount of difference, and correlates to similar magnitudes of structural changes seen in Alzheimer's disease, frontotemporal dementia (FTD), and schizophrenia (although in different brain regions).  

The right hemisphere of the brain is responsible for most of the tasks of attention and visuospatial memory.  Inattention and slight memory impairment occur symptomatically in individuals with depression, and was found to be higher in the high risk individuals as compared to the low risk individuals in Peterson et al.'s study.  The authors note that inattention could also be produced for social and emotional stimuli, thus producing depressive symptoms or MDD.  

It might be too early to state any translational or policy implications from this study, however more light is now shed upon the physiological differences in those at risk vs. not at risk for depression.  These results might be of interest for those with a family history of major depressive disorder who are curious about assessing their future risk of depression.  Check your cortical thickness.   Or don't...and hope your positive environment will reduce your risk.

Peterson BS, Warner V, Bansal R, Zhu H, Hao X, Liu J, Durkin K, Adams PB, Wickramaratne P, & Weissman MM.  Cortical thinning in persons at increased familial risk for major depresssion.  Proc Natl Acad Sci USA. 2009 Apr 14;106(15):6273-8

www.pnas.org