Research on the causes of autism is still at the stage where many etiologies seem possible. Althought a genetic link is likely, it may play a role of predisposition to another factor rather than being the only necessary and sufficient cause of autism.

One such connection being explored is the role of gastrointestinal infections in promoting autistic type behaviors.

This blog entry written by an occupational therapist refers to improvement in a young patient’s autistic type behaviors after she was treated for a Clostridium Bacteria infection.

The most recent blood tests found raging internal infections in little Miss S! Infection so out of control that the levels have to be brought down through dietary supplements before they can medicate her, so that she doesn’t go into a coma! Her infection is in the Clostridium family- from the makers of the hospital-dreaded C.Diff. New doctor sez that there are studies that connect clostridium infections with autistic symptoms in previously healthy rats. I found this abstract (but, since I am no longer a student, I no longer have awesome online library access, and cannot access the whole article). Anyway, this guy is saying that a chronic C. tetani infection (also causes tetanus) is linked to an increase in stereotypical autistic behaviors. The doctor told mom that curing this infection won’t ‘take away the autsim’ but could reduce some of her behaviors and improve some of her skills. I had never even heard of this, but will be anxious to see the results. Miss S’s diet changes have had incredible effects on her behavior, and though the RD at the hospital tells me that while there’s no evidence to support these diets, the anecdotes are highly supportive.

The theory that gut infections with Clostridia play some sort of role, particularly in late-onset autism is explored in articles like this one (Med Hypotheses. 2008;70(3):508-11.):

Therapy and epidemiology of autism–clostridial spores as key elements.”

… intestinal bacteria, specifically clostridia, may play a role in certain cases of autism and hypothesizes that the clostridial spores (which are notably resistant to antimicrobial agents and commonly used germicides) are involved in: (1) relapse in the autistic subject after a response to an agent such as oral vancomycin, after the drug is discontinued, (2) the unexplained increased incidence of autism in recent years, and (3) the unexplained increase in numbers of multiple cases in the same family…

However another article (Acta Paediatr. 2007 Jul;96(7):1076-9.) found no indications of active intestinal inflammation in 22 out of 24 autistic children they studied:

…One child who previously had a severe Clostridium difficile infection displayed raised levels of both these inflammatory markers and one child with extreme constipation for whom only calprotectin was possible to measure had raised levels. The remaining children displayed results that did not indicate an active inflammatory status in the intestine when the two inflammatory markers were combined. …

No evidence for a clear link between active intestinal inflammation and autism based on analyses of faecal calprotectin and rectal nitric oxide.

Several articles mention the benefit of therapy with the antibiotic Vancomycin in late-onset autism:
Short-term benefit from oral vancomycin treatment of regressive-onset autism.” (J Child Neurol. 2000 Jul;15(7):429-35.)

“…a subset of children appears to develop normally until a clear deterioration is observed. Many parents of children with “regressive”-onset autism have noted antecedent antibiotic exposure followed by chronic diarrhea. We speculated that, in a subgroup of children, disruption of indigenous gut flora might promote colonization by one or more neurotoxin-producing bacteria, contributing, at least in part, to their autistic symptomatology….”

“…Entry criteria included antecedent broad-spectrum antimicrobial exposure followed by chronic persistent diarrhea, deterioration of previously acquired skills, and then autistic features. Short-term improvement was noted using multiple pre- and post-therapy evaluations …”

For more articles on this topic, see late-onset autism and clostridia