Researchers at the Western Australian Centre for Health & Aging have identified a genetic variation in the C-reactive protein gene that predisposes individuals to developing depressive symptoms.
C-reactive protein (CRP) is a ubiquitous protein that is an acute marker for physical ill health and is up-regulated in response to stressful events, including inflammation or infection.
Previously published research examining inflammatory molecules involved in depression suggested an association between CRP and depression.
However, when researchers at the Western Australian Centre for Health & Aging (WACHA) studied this association, they found that once physical morbidity was taken into account, the association between CRP and depression disappeared.
“This particular association could have been confounded just by poor physical health and it was the poor physical health that was contributing to people being depressed rather than the CRP per se increasing depression,” says Professor Osvaldo Almeida, the director of research at WACHA.
“But we were not entirely satisfied with this (finding) because even though poor physical health might contribute to causing depression there would be physiological intermediates in this relationship that could be contributing to people becoming depressed and CRP could be one of them.
“My concern was that we were potentially hiding an effect that was real even though it may have been caused by poor physical health.”
Researchers at WACHA recruited a cohort of community dwelling older men (70+) in Perth as part of the ‘Health in Men Study’. They performed genotyping studies, measured CRP levels and assessed depression levels using a Geriatric Depression Scale, in an effort to understand the role of CRP in depression.
“What we found in this particular piece of research was that the genetic variation in the CRP gene dampens the CRP response. In other words, it decreases your ability to fight off stressful events efficiently and this is associated with depressive symptoms.
“The association between CRP and depression becomes more prominent the sicker the person gets.”
According to Professor Almedia, this particular genetic variation is likely to increase the susceptibility of people to develop depressive symptoms because they don’t become acutely sick as people who don’t have the variation, as the stressful event is not dealt with acutely as it should be.
Instead, the damage tends to persist and leads to prolonged levels of changes in the body that leads to sickness behaviour later which Professor Almedia describes as similar to symptoms of depression.
“Many of these things mentioned in sickness behaviour are also similar in people who develop depressive symptoms. People become depressed, withdraw, lose interest in the surrounding environment, lack motivation and lack energy.”
The research was supported by the National Health and Medical Research Council of Australia, and was published in the International Journal of Epidemiology (11 May 2009).
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