What if the microbes in your gut could act as an early warning system, alerting you that you might develop Alzheimer’s disease? It may sound unlikely, but recent research have found that certain microbes are more common in those with very early signs of the disease, pointing to a potential new method for diagnosing a disease that affecting millions worldwide.
The gut microbiome is the collection of microbes, which include bacteria, viruses and fungi, in the gut. Having different populations of microbes is thought to be important for our overall health. However, under certain circumstances, the gut microbiome may also contain microbes that are harmful to our health.
IN Alzheimer’s, two proteins, known as amyloid-beta and tau, accumulate abnormally in the brain. Their presence results in the characteristic memory loss and cognitive decline associated with the disease, with symptoms becoming progressively worse over time.
It is known that amyloid-beta and tau begin to accumulate long before the start of Alzheimer’s symptoms. It is at this stage (known as the “preclinical stage”) that researchers saw changes in the gut microbiome.
The researchers found clear differences in the gut microbiome profiles in older people with and without signs of preclinical Alzheimer’s. In those with signs of preclinical Alzheimer’s, the differences in the gut microbiome appeared to be linked to the accumulation of amyloid-beta and tau proteins in the brain.
Doctors currently rely on the results of various diagnostic tests to assess whether someone may have preclinical Alzheimer’s. The researchers combined these findings with their participants’ gut microbiome data and fed it into a machine learning algorithm, a computer program that can make predictions based on the data you give it.
They found that including the gut microbiome data improved the algorithm’s ability to accurately diagnose preclinical Alzheimer’s. This remained the case even when not all of the diagnostic test data were included.
Some of the diagnostic tests for preclinical Alzheimer’s can be uncomfortable, e.g lumbar punctureor rely on expensive imaging technologies such as magnetic resonance imaging (MRI) scanners that have access to known to be unequal globally.
The idea of analyzing a person’s gut microbiome, requiring only a stool sample, to assess their risk of developing the disease is appealing. It would offer a non-invasive, more accessible way to identify those at risk of developing Alzheimer’s at an earlier stage, giving them more time to plan and prepare for the future.
However, it should be noted that the improvement the study found in predicting preclinical Alzheimer’s by including gut microbiome data was quite modest. So while analysis of gut microbiome data may complement existing methods for diagnosing preclinical Alzheimer’s, it cannot yet replace them.
Unexpectedly, some of the species found to be associated with signs of preclinical Alzheimer’s were previously thought to be beneficial to human health. One of those identified is a bacterium known as Faecalibacterium prausnitzii (F. prausnitzii), Which one, in a previous studywas found to be more common in the human gut microbiome without Alzheimer’s compared to those with the disease.
It is unclear why what are considered to be potentially beneficial microbes were associated with those with symptoms of preclinical Alzheimer’s, as opposed to those who were cognitively healthy.
One explanation may be the stage of the disease. It is important to recognize that not all who have signs of preclinical Alzheimer’s will go on to develop Alzheimer’s themselves. There may be changes in the gut microbiome that occur in later stages of the disease, such as loss of F. prausnitzii.
While it may be tempting to conclude that the gut microbes identified as being associated with signs of preclinical Alzheimer’s also contribute to the development of the disease, the study provides no evidence of a cause-and-effect relationship.
But if a connection can be established, it opens up the exciting possibility that future treatments for Alzheimer’s could target the microbes in our gut.
Article written by Catherine PursePhD candidate in microbiology, The Quadram Institute
You may also be interested in: