Australian scientists have found a strong genetic overlap between depression and a number of diseases of the gastrointestinal tract. The results may help to better understand why mental and physical illnesses often occur together.
The study, published in the scientific journal “Nature Genetics“, analyzed the genetic links between major depressive disorder and four main groups of diseases: cardiovascular, metabolic, gastrointestinal and immune.
The scientists found common genetic factors in all the groups studied, but the strongest link was between depression and diseases of the digestive system. Among them are irritable bowel syndrome, gastroesophageal reflux disease, gallstone disease and peptic ulcer.
The analysis showed significant overlap between genetic variants associated with the risk of these diseases and genetic factors that increase the predisposition to depression.
According to lead author Damien Woodward, the results support the idea that that depression should not be viewed solely as a brain-related illness.
Of particular importance may be the so-called gut-brain axis“, the two-way communication system between the central nervous system and the gastrointestinal tract. It involves the nervous system, hormones, immune mechanisms and intestinal microbiota. Scientists believe that common biological mechanisms may partly explain why people with depression are more likely to suffer from certain physical illnesses.
The discovery may also have implications for future treatment. Identifying common genetic and biological mechanisms could help develop therapies that affect both mental and physical health.
Researchers are also looking at the possibility that drugs already approved for certain diseases could be tested for use in other conditions if they are found to affect the same biological pathways.
However, the results do not mean that a gastrointestinal disease necessarily causes depression or vice versa. Genetic overlap indicates the presence of common risk factors, but does not in itself prove a causal relationship.