Is there a link between autism spectrum disorder and the gut microbiome?

The gut microbiome of children with autism spectrum disorder (ASD) has been found to be different when compared to typically developing children.

The relationship between ASD and the gut microbiome is not well understood. That said, a recent study performed at the California Institute of Technology examined the behavioral effect of transplanting gut microbiota from children with ASD into mice, and the results suggested a causal link between ASD and certain types of microbiota.

In the following article, we summarize the findings of the study and explore potential treatments based on its results.

Are ASD and the Gut Microbiome Connected?

Before we dive into the research, let’s review the basic definitions of both ASD and the gut microbiome.

ASD is a neurodevelopmental condition characterized by deficits in social interaction and communication with restrictive repetitive behaviors. The CDC currently estimates that ASD affects 1 in 36 children in the United States.

The gut microbiome consists of over 100 trillion microbial cells with over 2,000 different species. There are more bacteria in the gut than cells in the human body. These bacteria engage in various physiological processes including digesting food, creating neurotransmitter precursors, producing vitamins, and playing a role in immunity. Numerous factors such as diet and who lives with you (including pets) can impact the microbiome over time.

Many patients with ASD have been found to have gastrointestinal (GI) disorders. However, having both an atypical composition of gut bacteria and ASD does not mean one may cause the other. The study described below sought to clarify the relationship between the two and demonstrate whether this relationship was causal or not by implementing a novel experiment. Read on to find out the fascinating results.

Studying the Link Between the Gut Microbiome and ASD in Mice

Prior studies have demonstrated that mice develop behavioral symptoms when they receive microbiota from patients with depression, anxiety, or schizophrenia. This study sought to determine if the same phenomenon would occur when mice received microbiota from patients with autism.

To conduct this study, scientists colonized germ-free (GF) mice with a fecal transplant containing gut microbiota from one of two different patient groups: a control group made up of “typically developing” individuals and an ASD group made up of individuals with autism. Since ASD is a neurodevelopmental disorder that presents early in life, the mice were then bred so scientists could examine the effects of fecal transplants on mice offspring. Here’s what the study found:

  • The offspring of mice given a transplant from the ASD group demonstrated increased repetitive behaviors. Interestingly, behavioral changes were more pronounced in male mice, which correlates with the distribution in ASD population studies. Currently the overall male-to-female ratio of ASD is 3.8 to 1 based on the latest CDC statistics.
  • Certain bacteria in the gut were less prevalent in the mice and offspring colonized with microbiota from the ASD group versus the control group. Most notably, the ASD-colonized mice displayed less Bacteroides and Parabacteroides than the control group mice. The presence of these two bacterial strains correlated with reduced repetitive behaviors and increased social behavior in mice.
  • The ASD-colonized mice also displayed a greater number of E.tayi bacteria than the control group. E.tayi correlated with increased repetitive behaviors and deficits in social interaction.
  • The authors also found differences in concentrations of several amino acids between the two groups. 5-aminovaleric acid (5AV)—a weak gamma-aminobutyric acid (GABA) receptor agonist—was found to be lower in the ASD group. Another weak GABA agonist, Taurine, was also found to be ~50% less in the ASD group compared to the control group of mice. GABA is a primary inhibitory neurotransmitter, and together these findings suggest that gut microbes can impact GABA signaling.

How Can the Results of This Study Benefit Autism Treatment Options?

The study authors hypothesized that providing depleted amino acids may have a protective effect from developing ASD symptoms. High concentrations of Taurine or 5AV administered to mice with ASD type symptoms were found to significantly reduce repetitive behaviors and increase social duration. The same treatment could benefit patients with autism.


This fascinating study demonstrated a link between gene expression and the gut microbiome. It also demonstrated that replacing certain amino acids such as 5AV and Taurine could help ASD symptoms in mice. Further studies will be needed to understand this connection and whether it holds true for humans. This study supports that there may indeed be a causative relationship between the gut microbiome and behavior.

To find out how this study could help you and your patient or child, contact our doctors at Potomac Psychiatry.