The Causes of Autism

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Study Finds Link Between Autism Severity and Gastrointestinal Health

Who are the remarkable authors, what is the title of the study, and what year was it published?

Authors: James B. Adams, Leah J. Johansen, Linda D. Powell, David Quig, and Robert A. Rubin

Title: Gastrointestinal flora and gastrointestinal status in children with autism–comparisons to typical children and correlation with autism severity. BMC Gastroenterology 2011, 11:22

Year: 2011

What is the study about?

This study focuses on the gastrointestinal flora and gastrointestinal status in children with autism, comparing them to typical children and correlating them with autism severity. Specifically, it examines the prevalence of dysbiotic bacteria, levels of inflammation markers and other biomarkers, mucosal status, and digestive enzyme activity in stool samples collected from children with autism and typical children. The study is designed to provide greater clarity regarding the impact of autism on GI (gastrointestinal) health. Autism is often associated with gut issues such as constipation or diarrhea, and issues related to feeding and food aversions. However, the extent and nature of this connection are not well established. This study aims to provide some insight into the extent to which autism and GI problems are correlated and to which they co-occur, and build upon previous research in this area.

What previous research is there on this topic?

One study in 2003 found that 24% of 137 children with ASD had at least one GI symptom, with diarrhea being the most common (occurring in 17% of individuals). In 2006, a study of 150 children (50 ASD, 50 typically developing, and 50 children with other developmental disabilities) found that 70% of children with ASD presented with GI symptoms, compared to 28% of typically developing children and 42% of those with other developmental disabilities. Another study conducted by the authors’ group in 2006 of 51 children with ASD found that 63% of children with autism were reported to have moderate or severe chronic diarrhea and/or constipation, compared to only 2% of the control group. A characterization study in 2008 of 160 children with ASD found that 59% had GI dysfunction, with diarrhea or unformed stools, constipation, bloating, and/or gastroesophageal reflux (GERD) being the most commonly reported symptoms. Similarly, a 2009 study of 172 children with autism spectrum disorder found that 22.7% had GI distress, with diarrhea and constipation being the most prevalent symptoms.


A study published in 2002 studied fecal samples from 13 children with late-onset autism and 8 control children, finding that the number and type of Clostridium and Ruminococcus species in children with autism differed from the control children. Another study in 2004 followed up this study using stool samples from children with autism and found that Clostridium cluster groups I and XI and Clostridium boltae had mean cell counts significantly higher than those of control children. Another study in 2005 reported differences in the gut microflora of children with autism compared to healthy children using fluorescence in situ hybridization (FISH) targeting Clostridium groups. In their study, levels of the Clostridium histolyticum group of bacteria were higher in the autism spectrum disorder (ASD) children compared to typical children.

A study in 2010 investigated gut bacteria in children with autism vs. controls, using high throughput sequencing techniques and found several differences at the phylum level. Additionally, Desulfovibrio species and Bacteroides vulgatus were present in higher numbers in autistic than controls. Treatment studies using an oral antibiotic (vancomycin) to treat abnormal gut flora showed significant temporary improvements in behavior for children with late-onset autism. However, this study demonstrated the importance of gastrointestinal flora and the difficulty in permanently normalizing them.

Much focus has been given to the presence and abundance of Clostridium groups in the intestines of autistic children. One study in 2008 hypothesized that the relapse of some autistic kids after antibiotic treatment is caused by the presence of Clostridium spores. This study also discussed the fact that propionate has been shown to have severe neurological effects in rats, and Clostridia species are propionate producers. No human studies have been conducted to test whether the relative proportion of propionate and/or its absolute concentration correlates to autistic symptoms. However, a study in 2007 demonstrated that injecting propionate directly into specific regions of rat brains in vivo can cause significant behavior problems.

There have also been reports of decreased activity of digestive enzymes in children with autism. A study in 2002 reported that 49% of children with autism who underwent endoscopy had deficiencies in one or more disaccharidase enzymes, especially lactase and maltase. They reported that all of the children with low enzyme activity had loose stools and/or gaseousness. Another study of children with autism and their first-degree relatives found that 37% and 21%, respectively, had increased intestinal permeability based on a lactulose/mannitol test, compared to 5% of normal subjects. They also found that autistic patients on a gluten-free, casein-free diet had significantly lower intestinal permeability.

What methods were used?


The participants were 58 children with ASD and 39 typically-developing children between the ages of 21/2 and 18 years. All participants were required to have not used any antibiotics or antifungal medications in the prior month. The authors note that the two groups were similar in age, but the control group had a higher percentage of females and a lower severity of gastrointestinal (GI) problems compared to the ASD group.

The autism group was split into three groups based on their consumption of seafood and fish oil. The three groups were: 1. A-Fish: This group consumed seafood more than twice a month, and 57% of them also consumed fish oil on a daily basis. 2. A-Fish Oil: This group did not consume seafood but took fish oil supplements daily. 3. A-No Fish: This group did not consume seafood or fish oil. It is worth noting that none of the typical group were consuming fish oil regularly.

Dependent Variables

This study analyzed various dependent variables through lab analysis of stool samples and parent-reported questionnaires. The analyzed variables include biomarkers associated with inflammation, oxidative stress, or bacterial overgrowth, such as lysozyme, lactoferrin, E. coli, and Enterococcus. The stool samples were sent to Doctor’s Data, which is a certified laboratory under the CLIA program and conducted all lab measurements in this research. In addition, this study used the 6-GSI score questionnaire to measure the severity of gastrointestinal symptoms, such as chronic diarrhea or constipation, in individuals with autism.


Additionally, the questionnaire asked about fish oil consumption, probiotic usage, and gluten-free or casein-free diets. The study compared the 6-GSI total scores and four subscales among different groups of participants. Moreover, the study examined the levels of Clostridium species, including C. histolyticum, C. ramosum, and C. difficile, which have previously been linked to autism-related GI problems. Understanding the critical variables analyzed in this study, such as biomarkers and the 6-GSI score, can help assess the link between GI problems and autism severity, and help identify potential biomarkers that could benefit future GI research.

Severity of Autism

Autism Treatment Evaluation Checklist (ATEC), an instrument which was designed to provide a quantitative assessment of autism severity. It is composed of four subscales: 1) speech/language/communication, 2) sociability, 3) sensory/cognitive awareness, and 4) health/physical behavior. The sum of the scores for each subscale gives the total ATEC score.

ATEC scores were used to assess the severity of autism in children by their parents or caregivers. The scores were obtained through a questionnaire that was filled out by parents of children with autism. The ATEC scores were then compared between two groups: a group of children with autism and gastrointestinal problems, and a control group of typical children.

What were the findings?

Gut Bacteria

Children with autism and GI problems had lower levels of beneficial gut bacteria such as bifidobacteria and lactobacillus, and higher levels of potentially harmful bacteria such as clostridia and desulfovibrio.

The study found that the autism group had lower levels of lysozyme in their gastrointestinal flora compared to the control group. The lower levels of lysozyme were associated with probiotic usage, which suggests that probiotics may have decreased the need for lysozyme to be excreted to defend against pathogenic bacteria.

GI Problems

The study results showed that the overall ATEC scores in children with autism and GI problems were significantly higher than those of the control group. In particular, the speech/language/communication and sensory/cognitive awareness subscales of the ATEC showed the largest differences between the two groups.

Severity of Autism Symptoms

The authors of the study also found that the 6-GSI, an index of GI symptoms, strongly and significantly correlated with the total ATEC score. This finding suggests that the severity of GI problems has a significant impact on the severity of autism symptoms.

The study also showed that there was no significant difference in any biomarkers between the low-GI-problem and high-GI-problem groups.

Sex Differences

In the typical control group, there were no statistically significant differences in any biomarkers between males and females, except for possibly higher levels of yeast in females. However, in the autism group, there were too few females to justify comparing the males versus females.

Probiotic Usage

Furthermore, the authors also reported that probiotic usage was significantly greater in the autism group compared to the typical control group. Specifically, 71% of the autism group reported using probiotics, while only 16% of the typical group reported probiotic use. However, the authors did not find any significant differences in GI parameters, ATEC scores or the gut microbiome between those who used probiotics and those who did not.

Short Chain Fatty Acids (SCFA)

The study found a significantly lower total amount of SCFA, including lower levels of acetate, proprionate, and valerate. The lower level of SCFA’s may be due to probiotic usage (which were higher in the autism group), lower sacchrolytic fermentation by beneficial bacteria, lower intake of soluble fiber, prolonged transit time due to constipation, and/or increased absorption by the gut. However, further research is needed to determine the exact cause, as this study did not further examine these findings.


pH Levels

The study found that there was a broad distribution of pH levels in the autistic group which suggests a general disregulation of pH, possibly affecting digestion and bacteria. The fecal pH, which reflects colonic pH, was similar in both the autism and control groups, although the autism group had a somewhat larger standard deviation.

The pH level was negatively correlated with lysozyme, implying that higher pH is associated with lower levels of lysozyme and vice versa.

The study also found an even stronger negative correlation between pH and total SCFA, suggesting that SCFA’s contribute to colonic pH.

Additionally, the A-Fish Oil group had slightly higher pH values than the other two groups, and the higher pH values were associated with decreased levels of beneficial bacteria like Lactobacillus.

What are the study’s limitations?

The study diagnosed the participants with autism spectrum disorder before enrollment, and relied on parental report for the neurotypical children, with no additional verification. A limitation of the study was that children with autism had higher gastrointestinal problems and varying dietary habits, which complicated analysis, but provided valuable insights. Subgroup results should be interpreted cautiously due to smaller sizes and potential confounding variables. Larger, carefully designed studies are necessary to properly investigate these issues.

What are the implications of these findings?

Other research found that babies fed formula without lysozyme had 3 times the rate of diarrheal disease. For future research, the authors hypothesize that probiotics provide limited defense against bad bacteria, which may decrease the need for the immune system to excrete lysozyme.

The findings suggest that the reduced levels of SCFA’s in children with autism could be due to various factors, such as lower intake of soluble fiber, extended transit time, and/or increased gut permeability. This possibility is particularly interesting since previous research has shown that SCFA’s may induce autism-like symptoms in rats. In other words, if lower SCFA levels in the stool result from higher absorption, it may increase the levels of SCFA’s in the bloodstream and exacerbate autism symptoms. Further investigation is required to determine if SCFA levels in blood or urine samples can provide additional insights into the correlation between SCFA’s and autism.

Finally, while the study cannot establish a causal relationship between gastrointestinal problems and autism severity, it highlights the importance of addressing gut health in the context of autism and the potential for interventions such as probiotics and nutritional modifications to improve symptoms.

What other studies within the library is this one related to?

A study published in 2009 by the same lead author found there were multiple positive correlations between the severity of autism and the urinary excretion of some toxic metals.

A study published in 2021 found that taking antibiotics during infancy can cause a disruption in the normal gut microbial communities, which may lead to changes in brain development.

Another study published in 2021 found that antibiotics can significantly alter the types of bacteria present in the gut of developing mice, and these changes were more pronounced in mice whose mothers were also exposed to antibiotics during gestation. These differences in gut bacteria were also associated with changes in gene expression in parts of the brain involved in emotional regulation, which could potentially have long-lasting effects on behavior.

Can I read the study somewhere?

Of course. Right here.

Shh. Quiet in the hall.

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