Gut microbiome therapies show promise for treating autism
Therapies that target the gut microbiome through diet, prebiotics, probiotics, antibiotics or fecal microbiota transplantation could effectively treat autism spectrum disorders, but finding a “cheap and effective treatment” requires better designed and larger studies, according to researchers who reviewed more than 150 studies published since the 1960s.
While it is well established that gastrointestinal symptoms like diarrhea, constipation and flatulence are common comorbidities in patients with autism spectrum disorders (ASD), the underlying mechanisms remain poorly understood, investigators wrote. Accumulating evidence shows that the gut–brain axis may contribute to the development of ASD, they added, supporting the role of the gut microbiome in brain function and the view of the enteric nervous system as a “second brain.” In particular, they noted that increased intestinal permeability, or “leaky gut,” appears to be a fundamental underlying factor in patients with ASD.
“ASD is likely to be a result of both genetic and environmental factors [including] the overuse of antibiotics in babies, maternal obesity and diabetes during pregnancy, how a baby is delivered and how long it is breastfed. All of these can affect the balance of bacteria in an infant’s gut, so [they] are risk factors for ASD,” Qinrui Li, PhD, of the department of pediatrics at Peking University First Hospital in Beijing, China, said in a press release.
There are currently no effective therapies for ASD, but strategies to modulate the gut microbiota show potential for children with ASD, according to Li and colleagues.
“Efforts to restore the gut microbiota to that of a healthy person has been shown to be really effective,” Li said in the release. “Our review looked at taking probiotics, prebiotics, changing the diet — for example, to gluten- and casein-free diets — and fecal matter transplants. All had a positive impact on symptoms,” ranging from increased sociability, reduced repetitive behavior, and improved social communication.
The idea behind prebiotics and probiotics in ASD is that they may help regulate intestinal barrier function, the investigators wrote. While probiotics have been shown to normalize the gut microbiota and improve GI symptoms, there is less evidence for prebiotics.
Li and colleagues cited several small studies showing probiotics can improve GI and psychological symptoms, including a cohort study showing children with ASD had improved “ability to follow directions” after receiving probiotics for 2 months, and a case study showing 4 weeks of VSL#3 (VSL Pharmaceuticals) improved autistic core symptoms in a child with ASD. However, they concluded that large randomized controlled trials are lacking, and noted that a clinical study of probiotics in 100 preschoolers with ASD is currently ongoing.
Fecal microbiota transplantation
The investigators highlighted data supporting the high efficacy of FMT for Clostridium difficile infection, and the speculation that FMT can normalize the gut microbiota in patients with inflammatory bowel disease and irritable bowel syndrome. “Thus, researchers are increasingly interested in using FMT to treat children with ASD. However, the safety of FMT should be considered,” they wrote.
They cited one open-label clinical trial of microbiota transfer therapy, “a modified FMT protocol comprising 14 days of antibiotic treatment followed by bowel cleansing and the administration of a high initial dose of standardized human gut microbiota ... for 7-8 weeks.” In the study, this intervention normalized the gut microbiota, and improved GI symptoms and ASD-related symptoms in 18 children with ASD.
The rationale behind dietary therapies in children with ASD surrounds their likelihood of rejecting certain foods, thereby ingesting “fewer fruits, vegetables, and proteins” and “a significantly lower daily intake of potassium, copper, folate, and calcium,” which can influence the gut microbiota composition.
Li and colleagues cited one open-label trial that showed patients with ASD who were treated with omega-3 fatty acids for 12 weeks had significant improvements in social behaviors, but noted another recent study showed high-dose omega-3 supplements did not affect children with ASD.
Other studies have shown gluten-free and/or casein-free diets improved ASD behaviors, psychological symptoms and social behaviors, and the ketogenic diet showed improvements in an ASD animal model.
In terms of modulating the gut microbiome using antibiotics, Li and colleagues cited one study that showed children with regressive-onset autism who were treated with vancomycin had improved GI and ASD symptoms, and a randomized controlled trial that showed 3 months of treatment with levocarnitine improved ASD symptoms in children.
More research needed
Despite the recent clinical studies showing gut microbiome-targeted therapies can improve ASD symptoms, the researchers noted that these studies are scarce and small, and that larger clinical trials are necessary.
“We are encouraged by our findings, but there is no doubt that further work needs to be carried out in this field,” Li said in the press release. “We need more well-designed and larger-scale studies to support our theory. For now, behavioral therapies remain the best way to treat ASD. We would hope that our review leads to research on the link between the gut microbiota and ASD, and eventually a cheap and effective treatment.” – by Adam Leitenberger
Disclosures: The researchers report no relevant financial disclosures.