Autism Linked to Lower Levels of Distinct Gut Bacteria

Fran Lowry

July 10, 2013

Children with autism appear to have distinctly different levels of intestinal flora, which may increase their vulnerability to pathogenic bacteria and perhaps play a role in autism pathogenesis, new research suggests.

In a small study, investigators at Arizona State University in Tempe found that autistic children had significantly fewer types of 3 critical types of gut bacteria compared with normal control individuals.

"[We] demonstrated that autism is closely associated with a distinct gut microflora that can be characterized by reduced richness and diversity as well as by altered composition and structure of microbial community," the authors, led by Rosa Krajmalnik-Brown, PhD, write.

"Most notably, we also discovered that the genera Prevotella, Coprococcus, and unclassified Veillonellaceae were significantly reduced in autistic children," they add.

The study was published online July 3 in PLoS One.

GI Disorders Common

Gastrointestinal (GI) disorders are frequent in children with autism, and many researchers believe there may be a link between autism and abnormalities in gut microbial functions.

Another study also recently published in PLoS One and reported by Medscape Medical News showed that a subset of children with autism have increased immune reactivity to gluten that is unrelated to celiac disease.

In the current study, the researchers note that recent high-throughput sequencing analyses indicate that disturbances in the composition and diversity of gut microbiome are linked to various disease conditions.

However, microbiome-level studies in autism are limited, and the few that exist focus on pathogenic bacteria.

To address this research gap, the researchers analyzed the gut microflora from fecal samples taken from 20 healthy and 20 autistic individuals aged 3 to 16 years, using pyrosequencing.

They found that the participants with autism had a lower diversity of gut microbiomes compared with healthy control individuals — specifically, lower levels of Prevotella, Coprococcus, and Veillonellaceae.

"The 3 genera represent important groups of carbohydrate-degrading or fermenting microbes," Dr. Krajmalnik-Brown said in a statement.

"Unexpectedly, these microbial changes were more closely linked to the presence of autistic symptoms rather than to the severity of GI symptoms and specific diet/supplement regimens," the authors note.

"Such bacteria could be critical for healthy microbial-gut interactions or play a supportive role for a wide network of different microorganisms in the gut. The latter would explain the decreased diversity observed in autistic samples," she said.

Prevotella was the most conspicuously reduced among the autistic patients in this study.

Dr. Krajmalnik-Brown noted that Prevotella is believed to play a key role in the composition of the human gut microbiome and is common in normal children with more diverse and robust microbial communities.

"We think of Prevotella as a healthy, good thing to have," she said.

Intriguing Results

Armin Alaedini, PhD, from Columbia University Medical Center, New York City, who led the earlier study that found an association between gluten sensitivity unrelated to celiac disease and autism, described the results of this study "intriguing, as they further indicate a link between autism and gastrointestinal abnormalities, particularly emphasizing the relevance of gut microbial diversity in the affected children.

However, he pointed out that a limitation of the study was that it did not include a control nonautism group with GI symptoms.

"Therefore, it is not totally clear whether the observed differences in the gut microbiome are specific to autism or if they are associated with GI symptoms in general," he said.

The study was funded by Autism Research Institute, San Diego, California. Dr. Krajmalnik-Brown and Dr. Alaedini report no relevant financial relationships.

PLoS One. Published online July 3, 2013. Full article

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