"The Role of the Gut
Microbiome in Autism" There are many examples in nature of intestinal microbes altering host behavior. One such example involves the
brain parasite Toxoplasma. When it infects a rodent through the gut, it finds its way into the brain and causes the animal
to lose its innate fear of the odor of bobcat urine. Why does the parasite care
about what mice are afraid of? Because by not avoiding predators, they’re more often caught and eaten; so, the parasite can then go on to infect other rodents. If you’re a mouse brain parasite, how are you going to spread? Mice aren’t cannibals; so, you have to make sure the mouse you’re in is eaten by something else.
So, the parasite evolved a way to alter the mouse’s behavior. Given the potential power of microbes to affect behavior, might the disruption
of our gut microbiome, our good gut bacteria, be a potential factor in
the causation of autism? Where’d they get that idea from? Well, kids with autism do tend to have altered gut flora, different than that of children without autism, for example, significantly less Prevotella in autistic children,
which, if you remember, characterized the healthy gut enterotype that you can foster the growth of yourself with a more plant-based diet. But, which came first? Instead of the bad gut
flora leading to autism, isn’t it more likely that the autism led to the bad gut flora? Children with autism eat diets with significantly fewer
servings of fruits and vegetables, often characterized by a lack of variety, an inadequate amount
of fiber-containing foods, meaning whole plant foods in general, and an increased amount of added sugars.
So, couldn’t that explain the different gut flora right there? There are some perinatal risk factors for the development of autism, including premature birth,
low birth weight, and delivery by caesarean section— particularly the C-section. What does that have to do with the microbiome? Well, there may be a protective value offered by the maternal
vaginal microbiome that the infant misses out on when they instead come out through a surgical incision. But, during a C-section, the mothers are also sometimes placed under general anesthesia, and it’s possible that the anesthetics could affect the baby's brain before he or she is disconnected
from the maternal blood supply. To differentiate between
the two scenarios, we need a study that
compared autism risk between C-sections in which the mom just got an epidural or spinal block, versus C-sections under
general anesthesia, but there's never been such a study… until now. This study examined
the incidence of autism in infants delivered vaginally, by C-section with
just regional anesthesia, and by C-section with
general anesthesia.
And only those delivered by C-section under general anesthesia had higher risk, not those in C-sections where mom just got like an epidural; so, that would suggest
the C-section connection is more of an anesthesia drug exposure thing than involving the lack of vaginal flora exposure. This wasn't an interventional trial, though, in which mothers were
randomized into various groups, just an observational study. So, it’s possible the
increased autism risk has less to do with
the anesthetic itself than the pregnancy complications
that may have led to having to put the mother under. Either way, I’m not seeing
the microbiome connection. They’ve tried probiotics
for children with autism, and so far, they don’t
seem to have helped much.
Some families, in desperation,
have tried fecal transplants where they like beg the
neighbor kid to donate. It’s like what one
fly said to the other— is this stool taken? Not FDA-approved, though; so, families are forced to
go on the brown market… (ahem). It can all be traced back
to this remarkable study published in the Journal
of Child Neurology. Several parents of children with regressive-onset autism— meaning the kids started out acting normally before the autism struck— noted that it all seemed to start after their child had taken antibiotics.
They had gotten chronic diarrhea –autism isn’t the only thing
that can run in your genes…(ahem) suggesting the antibiotics had mucked with their gut flora,
and then came the loss of language, play, and social skills. Now, this could be a total coincidence, but it led this group of
pediatric gastroenterologists to speculate that maybe there was some sort of cause-
and-effect link there. Maybe by wiping out the good bugs, some bad bugs took hold, some neurotoxic bugs, and that led to the autism. If this were true, maybe they could clean the slate once again, another dose of antibiotics, but this time to try to clear out any bad bugs lurking down there. Might that reduce autism symptoms in these individuals? That would be groundbreaking. They put the kids on a powerful antibiotic called vancomycin, and 80% of the kids got better. But, within a few weeks
after the treatment, most of them slipped back towards their baseline, suggesting that perhaps the bad bugs got pushed down but not out.
This study was performed nearly 20 years ago and only had an “n” of 11, meaning it only looked at 11 kids. (The letter n is research-speak for the number of subjects in a study). Surely, by now, there’s been lots of larger studies done. But, in reality, there’s only been a single follow-up study published, and it had an n of 1. A case report of a child with autism improving on antibiotics
and a father’s quest to understand what it all may mean, written by the father himself, describing a dramatic improvement
in the child’s autism after taking amoxicillin.
When he talked to other
parents of autistic children, he was surprised to discover
that many of them routinely gave their children antibiotics
expressly for that purpose, though he also heard from other parents that felt that their children’s autism got worse after antibiotics, or that antibiotics were blamed for the emergence of the
disorder in the first place. But, that all speaks to the potential role of the gut flora, just reinforcing the notion. Other parents were talking about it, but then when he scoured the
medical literature to learn more, all he was able to turn up
was that 11-child study. How is it possible that there
hadn’t been follow-up studies? Here it was, right before his eyes, personally witnessing
evidence in his own child what this study had shown,
this seemingly intractable condition rapidly and dramatically ameliorated in response to an antibiotic—
at least in some children, but surprisingly there were no attempts to repeat that study.
Now, I think most parents would probably just count their blessings, that at least it worked on
their child and leave it at that, but not this parent. He started his own Autism
Research Foundation, with the mission of encouraging,
sponsoring, and communicating breakthrough autism research..
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