In an earlier post I described the so-called hygiene/old friends hypothesis.  According to this, modern hygienic living conditions have removed infectious agents and parasites which co-evolved with the human immune system and came to fulfill important regulatory functions. The result is the notable rise seen in immuno-regulatory disorders such as asthma, multiple sclerosis (MS), inflammatory bowel disease (IBD), and—even more controversially, major depressive disorder (MDD).

Recently, Kevin Becker and others have argued that this hypothesis might also explain the so-called “autism epidemic”—or at least, part of it. Becker points out that

  • asthma, allergies, bowel disorders, and immune system abnormalities are linked with autism
  • autism and asthma have similar ages of onset and are more prevalent in boys
  • reduced risk related to late birth-order in autism is also found in asthma and other immune disorders
  • increased neonatal head circumference is found in both autism and asthma
  • autism, like asthma and other immuno-regulatory disorders, is increasing
  • as with asthma, there may be an urban bias in risk of autism
  • autism and asthma share several genetic markers

An obvious—if somewhat against-the-grain—therapeutic insight suggested by this hypothesis is that restoration of such “old friends” by clinical infection might help. Introduction of intestinal worms has certainly been found to halt the progress of MS (although not, of course, to reverse it), and oral administration of pig whipworm eggs (Trichuris Suis), already known to be helpful in IBD, is being trialed as a treatment for autism.

A further point worth making is that, according to the imprinted brain theory and its distinctive diametric model of the mind, autism and psychoses such as schizophrenia are opposites of one another and are based on oppositely-acting brain systems and genes. As I point out in my book, a common protozoan parasite, Toxoplasma gondii, is known to be implicated in some cases of schizophrenia. According to the theory this is because it attacks the amygdala, a prime component of the so-called paternal brain. The theory claims that psychoses result from reduced paternal and/or enhanced maternal brain function, with autism being the other way round. Modern hygienic living conditions demonstrably reduce T. gondii infection, and to that extent may definitely have a role in reducing the incidence of schizophrenia in modern societies, as the theory predicts and as the facts suggest (see my earlier post).

However, does this also mean that what reduces schizophrenia risk in this way also increases that of autism? This is essentially what the hygiene/old friends insight reduces to, and if it were confirmed would be another stunningly counter-intuitive triumph of the diametric model. At the very least—and assuming the diametric model is correct—my point above about T. gondii being responsible for some schizophrenia implies that, in those with over-active or over-developed paternal brain systems and a consequent risk of autism, the outcome of such an infection might be protective in some cases. I hasten to add that I am not advocating that autistics should infect themselves with this parasite as one correspondent suggested in relation to an earlier post about this!

On the contrary, the parallels with asthma and other auto-immune disorders suggest that much more than the amygdala is involved, and that dysregulation of the immune system may in itself be a factor in at least some cases of autism. Nevertheless, the fact that clinical infection with pig whipworm is already being tested as a therapy for autism suggests that my point is not completely foolish in principle, and who knows what future therapeutic interventions may follow?

In conclusion, the autism-resembles-asthma-in-being-a-disorder-of-the-modern-environment idea may be even more compatible with the imprinted brain theory than the parallel hypothesis about MDD discussed in an earlier post. But if so—and like other hypotheses such as the extreme male brain theory of autism—it is a part of a much bigger picture: one which only the imprinted brain theory and the diametric model of the mind can reveal in its entirety.  

(With thanks and acknowledgements to Kevin Becker and Graham Rook.)

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