The review, carried out by researchers from Peking University in China, looked at a wide range of studies on the topic to determine whether gut microbiota really could be the answer to preventing or reducing symptoms of autism.
“To date there are no effective therapies to treat this range of brain developmental disorders. The number of people being diagnosed with ASD is on the rise. As well as being an expensive condition to manage, ASD has a huge emotional and social cost on families of sufferers,” said Dr Qinrui Li, one of the researchers.
In their review, researchers found that the cost of caring for a child with ASD is £0.92 million in the UK - with the main costs related to special education services and a loss of parental activity.
However, multiple studies have demonstrated that gastrointestinal symptoms are more frequently occurring in children with ASD compared to their unaffected siblings. In fact, studies on the matter have been carried out since the 1960s, with many suggesting a relationship between heathy gut microbiota variety and autism.
Now, experts have suggested that approaches that look to re-shape the gut microbiome could be a cheap and effective method to reducing autism symptoms.
Qinrui and colleagues said all information supports a theory that gut microbiota is associated with ASD - noting that many recent clinical trials have shown the improvements of ASD symptoms from using gut microbiota modulation.
However, more research needs to be done, they noted: “Well-designed research studies with more participants are needed to provide more evidence that supports the effectiveness of these treatments."
An imbalance in the gut microbiota can be caused by both environmental and genetic factors, including the overuse of antibiotics in babies, maternal obesity and diabetes during pregnancy, as well as how a baby is delivered and how long it is breastfed, said the team behind the review.
Gastrointestinal symptoms are well reported with ASD sufferers, with many experiencing problems like diarrhoea, constipation and flatulence. Furthermore, ASD patients who also suffer from gastrointestinal symptoms are more likely to show anxiety, self-injury or aggression.
As a result, it is now assumed that gut microbiota is associated with ASD, either directly or indirectly, said Qinrui and colleagues.
For example, one recent study showed that the gut microbiota of children with ASD is less diverse and exhibits lower levels of Bifidobacterium and Firmicutes, as well as a higher level of Lactobacillus, Clostridium, Bacteroidetes, Desulfovibrio, Caloramator and Sarcina.
It was also found that infants who were delivered by Caesarean section are at higher risk of developing ASD than infants delivered vaginally, and sufferers of ASD usually have a history of using more antibiotics.
The review states that the gut is considered as a ‘second brain’, due to the gut brain axis being regarded as a pathway of communication between the gut and the brain.
In this way, the gut microbiota influences brain function through the neuroendocrine, neuroimmune and autonomic nervous systems and via microbiotic toxin production.
Animal studies have shown that ASD sufferers have defects in their gastrointestinal barriers, affecting the gut brain axis due to the resulting entry of toxin and bacterial products into the bloodstream.
Likewise, a human study detected higher concentrations of total short chain fatty acids and ammonia in fecal matter from children with autism compared to those without.
As a result there is now accumulating evidence pointing to the possibility of gut microbiota modulation as a potential therapy for autism.
Probiotics, prebiotics, fecal microbiota transplantation (FMT) and diet have all been getting considerable attention in this area.
The researchers commented that although there have been a lot of studies carried out on the effects of probotics, the effects of prebiotics are little known.
However, one large-scale study found that the daily administration of Delpro, a probiotic and immune modulator co-formulation, significantly improved both gastrointestinal and ASD symptoms.
FMT, administrating healthy fecal microbiota to a patient with a dysbiotic gut microbiota, has been studied extensively in regard to treating inflammatory bowel disease but not a lot has been tested on ASD patients so far.
However Li et al. said researchers are “increasingly interested in using FMT to treat children with ASD”, but commented that the safety of this method should be considered due to its adverse effects including abdominal discomfort and diarrhea.