Scientists Debunk Gut Microbiome-autism Connection

There's no technological grounds that nan gut microbiome causes autism, a group of scientists argue in an sentiment paper publishing November 13 successful nan Cell Press journal Neuron. They point to nan fact that conclusions from past investigation that supported this hypothesis-including observational studies, rodent models of autism, and quality objective trials-are undermined by flawed assumptions, mini sample sizes, and inappropriate statistical methods. 

Despite what you've heard, read, aliases watched connected Netflix, location is nary grounds that nan microbiome causally contributes to autism. I don't think it's warranted to spend further clip and backing connected this topic. We cognize that autism is simply a powerfully familial condition, and there's still loads to beryllium worked retired there." 

Kevin Mitchell, first writer and developmental neurobiologist, Trinity College Dublin

The hypothesis that autism is caused, at slightest partially, by nan gut microbiome stems from the truth that many people pinch autism suffer from gastrointestinal symptoms. In addition, the caller emergence in autism diagnoses has led immoderate to judge that environmental or behavioral changes are driving an increase in autism, though authors note that there is strong evidence that nan emergence successful autism diagnoses reflects accrued awareness and broadened diagnostic criteria rather than a biologic mechanism. 

Nevertheless, researchers person pursued nan microbiome-autism hypothesis by comparing the gut microbiomes of group pinch and without autism, by studying mouse models of autism, and by conducting clinical trials involving group pinch autism. The authors reason that in all of these studies, the results are flawed and unconvincing. 

"There's variability successful each 3 of those areas, and the studies just don't shape a coherent communicative astatine all," says elder writer and developmental neuropsychologist Dorothy Bishop of nan University of Oxford. 

In the astir highly cited studies comparing the gut microbiomes of group pinch and without autism, researchers used sample sizes ranging from 7 to 43 individuals per group, whereas statistical recommendations telephone for sample sizes successful nan thousands. 

"Autism is not rare, so there's nary logic to be having studies with only 20, 30, or 40 participants," says coauthor and biostatistician Darren Dahly of nan University College Cork. 

These studies besides used varying methods to qualify microbiome composition, which makes their results difficult to compare. And although some studies recovered differences between the microbiomes of people pinch autism and controls, these differences were often contradictory-for example, some studies found little microbial diverseness successful nan courage of group pinch autism, while others recovered nan opposite. These differences besides vanished erstwhile nan studies accounted for different variables, specified arsenic diet, aliases erstwhile they compared the microbiomes of children pinch autism with their neurotypical siblings. 

"If anything, location is stronger grounds for a reverse causal effect, successful that having autism tin impact someone's diet, which tin impact their microbiome," says Mitchell. 

Mouse models of autism that have claimed to show a nexus betwixt nan gut microbiome and autism are besides unconvincing, nan researchers say, because of behavioral, cognitive, and physiological differences betwixt humans and mice. 

"There's no grounds that 'autistic-like' behaviors successful mice models have immoderate relevance to autism, and nan experiments themselves had methodological and statistical flaws that undermine their claims," says Mitchell. 

Several quality objective tests person tested nan microbiome-autism presumption by performing fecal transplants aliases by administering probiotic therapies to group pinch autism and then monitoring changes successful their characteristics. Again, nan researchers opportunity that most of these studies used inadequate sample sizes and inappropriate statistical methods that undermine their findings, and many didn't use a power group aliases randomization. 

 "The statement crossed nan studies that we surveyed is that erstwhile you do nan tests properly, you don't see anything," says Dahly. 

Based connected nan deficiency of convincing evidence, and nan deficiency of advancement successful nan field, nan researchers argue that nan hypothesis that nan microbiome causes autism has reached a dormant end. 

"If you judge our message, there's two ways you tin go. One is to conscionable extremity moving connected this area, which is thing that we would beryllium rather happy to see," says Bishop. "But fixed that realistically, group are not going to stop, they need to at least start doing these studies successful a overmuch much rigorous way."