A novel study has identified common genetic factors that are present in both depression and Alzheimer’s disease.
Previous research employing epidemiological data has inferred an association between depression and Alzheimer’s disease – a neurodegenerative disease that is characterised by worsening dementia, with reports estimating that over six million people in the US alone have the disease.
Now, in a groundbreaking discovery, US researchers have discovered common genetic factors shared by depression and Alzheimer’s disease. Moreover, the team identified that depression played a causal role in the development of Alzheimer’s disease, and people with more severe depression experienced a more rapid memory decline.
Aliza Wingo, MD, of Emory University School of Medicine and the co-senior author of the study, said: “It raises the possibility that there are genes that contribute to both illnesses. While the shared genetic basis is small, the findings suggest a potential causal role of depression on dementia.”
The study is published in Biological Psychiatry.
Depression and Alzheimer’s genetic factors
For their investigation, the team conducted a genome-wide association study (GWAS), a method that includes scanning the entire genome for regions of commonality associated with specific conditions. The results of the GWAS illuminated 28 brain proteins and 75 transcripts (messages that encode proteins) that were associated with depression.
Of these, the team discovered 46 transcripts and seven proteins linked to symptoms of Alzheimer’s disease, suggesting a shared genetic base for depression and Alzheimer’s disease, potentially triggering an increased risk for AD associated with depression.
Despite other studies examining depression and Alzheimer’s disease by employing GWAS, the team’s novel investigation was more comprehensive than previous attempts due to the researchers utilising larger, newly developed data sets that revealed more extensive and detailed information.
Thomas Wingo, MD, the co-senior author of the study, commented: “This study reveals a relationship between depression and Alzheimer’s disease and related dementia at the genetic level. This is important because it may explain, at least in part, the well-established epidemiologic association between depression and higher risk for dementia.”
Dr Wingo added: “This relationship raises the question of whether treatment of depression can mitigate the risk for dementia. We identified genes that may explain the relationship between depression and dementia here that merit further study. Such genes may be important treatment targets for both depression and reduction of dementia risk.”
John Krystal, MD, Editor of Biological Psychiatry, said: “The costs of ineffectively treated depression continue to mount. There has been increasing evidence that major depressive disorder increases the risk for Alzheimer’s disease, but little insight into this relationship. This innovative study, which links genetic risk mechanisms to molecular changes in the brain, provides the clearest link to date supporting the hypothesis that depression plays a causal role in the biology of Alzheimer’s disease.”
The researchers stated that their research does not suggest that if someone has a bout of depression, they will develop dementia, but indicates that not treating depression effectively may aggravate the biology of Alzheimer’s disease and exacerbate the onset of symptoms and increase the rate of functional decline.