April is World Autism Awareness Month, a period for raising awareness about the conditions that impact communication, social interaction and behavior and affect about 1 in 160 children worldwide and 1 in 44 in the US.
The interest in the potential link between autism spectrum disorders and the gut microbiome has exploded due to the high rates of occurring gastrointestinal symptoms in this patient population, as well as the growing interest in the gut-brain axis.
Despite that interest, small sample size and differences in study design have meant recent studies have not accurately pinpointed if and how the gut microbiome contributes to autism spectrum disorders (ASD) compared to children who are not diagnosed.
To fill the knowledge gap about the potential role the gut microbiome plays in ASD, Professor Jacob Gratten and colleagues from the University of Queensland analyzed 247 children aged between 2 and 17 years, which included ASD patients, siblings without a diagnosis and unrelated children without a diagnosis.
The authors collected stool samples to analyze microbial DNA from patients with and without an ASD diagnosis. They also analyzed stool consistency and other factors such as age, sex and sleep habits to better understand what affects the gut microbiome and behavior.
Surprisingly, in contrast to previous microbiome studies in ASD patients, the authors did not find a direct association between the gut microbiome and ASD, with the exception of the species Romboutsia timonensis, which was lower in ASD patients. In contrast, their data suggest that ASD-associated repetitive and restricted behaviors lead to reduced dietary diversity which, in turn, is associated with lower microbiome diversity. The results are not in agreement with recent studies that advocate for the gut microbiome as a potential therapeutic target for treating ASD.
Gratten and his team did observe a higher rate of loose stools in the subjects, which means they experienced less colonic absorption of water and a faster transit time, both of which affect gut microbiota diversity. That finding is in line with several other studies that have observed that ASD patients often suffer from gastrointestinal issues such as diarrhea, constipation and abdominal pain.
Although the authors could not identify a direct association between the gut microbiome and ASD, they uncovered that autism-related traits and preferences are linked to food preferences that result in a less diverse diet, which leads to a less diverse gut microbiome and diarrhea-like stool. This new study casts doubt on previous animal studies suggesting a causal involvement of the gut microbiota in ASD-related behaviors.
Yap et al., Autism-related dietary preferences mediate autism-gut microbiome associations, Cell (2021), https://doi.org/10.1016/j.cell.2021.10.015