Depression is a brain disease

In a genome-wide study, Perlis and colleagues found 17 genetic variations linked to depression at 15 genome locations. In addition to hinting at a link between depression and brain gene expression during development, there was also evidence of overlap between the genetic basis of depression and other mental illnesses. While the genome sites identified still account for only a fraction of the risk for depression, the researchers say the results support the strategy of complementing more traditional methods with crowd-sourced data.

To increase their odds of detecting these weak genetic signals, the researchers adopted a strategy of studying much larger samples than had been used in the earlier genome-wide studies. They first analyzed common genetic variation in 75,607 people of European ancestry who self-reported being diagnosed or treated for depression and 231,747 healthy controls of similar ethnicity. These data had been shared by people who purchased their own genetic profiles via the 23 and Me website and agreed to participate in the company’s optional research initiative, which makes data available to the scientific community, while protecting privacy.

The researchers integrated these data with results from a prior Psychiatric Genomic Consortium  genome-wide-association study, based on clinician-vetted diagnoses of more than 20,000 patients and controls of European ancestry. They then followed-up with a closer look at certain statistically suspect sites from that analysis in an independent 23 and Me “replication” sample of 45,773 cases and 106,354 controls.

“We hope these findings help people understand that depression is a brain disease, with it’s own biology,” said Perlis. “Now comes the hard work of using these new insights to try to develop better treatments.”

Hyde CL, Nagle MW, Tian C, Chen X, Paciga SA, Wendland JR, Tung J, Hinds DA, Perlis RH, Winslow AR. Identification of 15 genetic loci associated with risk of major depression in individuals of European descent. Nature Genetics, Aug 1., 2016. doi:10.1038/ng.3623

About the National Institute of Mental Health (NIMH): The mission of the NIMH is to transform the understanding and treatment of mental illnesses through basic and clinical research, paving the way for prevention, recovery and cure. For more information, visit the NIMH website.

Five Major mental disorders share genetic roots

Prior to the study, researchers had turned up evidence of shared genetic risk factors for pairs of disorders, such as schizophenia and bipolar disorder, autism and schizophrenia and depression and bipolar disorder. Such evidence of overlap at the genetic level has blurred the boundaries of traditional diagnostic categories and given rise to research domain criteria, or RDoC, an NIMH initiative to develop new ways of classifying psychopathology for research based on neuroscience and genetics as well as observed behavior.

To learn more, the consortium researchers analyzed the five key disorders as if they were the same illness. They screened for evidence of illness-associated genetic variation across the genomes of 33,332 patients with all five disorders and 27,888 controls, drawing on samples from previous consortium mega-analyses.

For the first time, specific variations significantly associated with all five disorders were among several suspect genomic sites that turned up. These included variation in two genes that code for the cellular machinery for regulating the flow of calcium into neurons. Variation in one of these, called CACNA1C, which had previously been implicated in susceptibility to bipolar disorder, schizophrenia and major depression, is known to impact brain circuitry involved in emotion, thinking, attention and memory – functions disrupted in mental illnesses. Variation in another calcium channel gene, called CACNB2, was also linked to the disorders.

Alterations in calcium-channel signaling could represent a fundamental mechanism contributing to a broad vulnerability to psychopathology, suggest the researchers.

They also discovered illness-linked variation for all five disorders in certain regions of chromosomes 3 and 10. Each of these sites spans several genes, and the specific causal factors within them remain elusive. However, one region, called 3p21, which produced the strongest signal of illness association, harbors suspect variations identified in previous genome-wide studies of bipolar disorder and schizophrenia.

Source: Jordan Smoller, M.D., Massachusetts General Hospital

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References

Cross-Disorder Group of the Psychiatric Genomics Consortium. Identification of risk loci with shared effects on five major psychiatric disorders: a genome-wide analysis. The Lancet, February 28, 2013

 

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