Genetic Link Adds to Gut-Brain Axis Theory in Alzheimer's Disease

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The same genes that send people to the bathroom with an irritable bowel syndrome flare-up may be involved in future brain health, according to a new study. Researchers have found a genetic correlation between individuals with gastrointestinal tract (GIT) disorders and Alzheimer’s disease (AD).

Analyzing years of genetic data from AD studies and similar data from six GIT disorders, the scientists at the Center for Precision Health at Edith Cowan University in Australia found that many disease-specific genes shared the same loci, or chromosomal location, in each group.

The researchers say it is the first comprehensive look at the genetic relationship between these disorders. Prior to this, it was widely believed that there was a link between gastrointestinal disorders and AD. A 2020 longitudinal study noted that people with irritable bowel disease were six times more likely to suffer from AD. But the gut-brain axis had not yet been examined on a genetic basis.

“The study provides a novel insight into the genetics behind the observed co-occurrence of AD and gut disorders,” Emmanuel Adewuyi, PhD, MPH, said in an interview with EurekaAlert. Adewuyi, a postdoctoral research fellow at the Center for Precision Health at Edith Cowan University, led the study.

The authors say that understanding the underlying genetics of AD can provide clues about how the disease works, which is largely a mystery. Treatment of the disease is increasingly urgent in a world with growing life expectancy and incidence of AD. By 2030, over 82 million people will likely suffer from AD, according to the 2015 World Alzheimer’s Report.

The Australian study relied upon previously performed genome-wide association studies. They searched data for patients with AD, gastroesophageal reflux disease, peptic ulcer disease, gastritis-duodenitis, irritable bowel syndrome, diverticulosis, and irritable bowel disorder.

The final cohort represented over 450,000 people. Of those analyzed, they found all the GIT disorders except irritable bowel disorder were correlated with AD.

One of the biological factors that underscored this relationship was the amount of abnormal cholesterol in both sets studied. From the study, It appears that altered cholesterol was a risk factor for both AD and gut disorders. Therefore, the authors suggest that next steps should investigate the use of statins, such as atorvastatin or lovastatin, which lower cholesterol to see whether they help protect the gut and, in turn, the brain.

Although these results point toward a correlation, the researchers caution that a causal relationship cannot be established between these two sets of disorders. The data advance the idea of the gut-brain axis but don’t show that GI problems cause AD or vice versa. Nor do the findings mean that someone with AD will always have gut problems or that a person with gut problems will develop AD.

The authors suggest the role of diet in health maintenance. They specifically highlight the Mediterranean diet, which is rich in natural fats and vegetables.

The study was independently supported. The authors report no relevant financial relationships.

Commun Biol. Published online July 18, 2022. Full text

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