Microbes and Mental Illness ~ National Institutes of Health - August 13, 2010

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August 13, 2010

Microbes and Mental Illness - Posted by Thomas Insel

Hints that some mental illness may be linked to infectious agents and/or autoimmune processes date back to at least the early 20th Century. In the 21st Century, the field of microbiomics, which is mapping the microbial environment of the human organism, may transform the way we think about human physical and mental development.1 It is already clear that 90% of “our DNA” is microbial, not human. “We” are, in fact, “super-organisms” made up of thousands of species, many of which are being identified for the first time. And there are persistent individual differences in our microbial ecology established early in life.

Insights from microbiomics have proven important for understanding obesity2 and Type 1 diabetes,3 but microbiomics has not yet been a focus for research on mental illness. Yet, there are many clues linking microbiology and mental disorders, such as epidemiologic evidence of increased risk for schizophrenia associated with prenatal exposure to influenza. Probably the most compelling case for such involvement is children who develop obsessive compulsive disorder (OCD) and/or tic disorders “overnight,” following a strep infection. Despite continuing debate over its parameters, evidence is mounting in support of Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal Infections (PANDAS) — or at least a syndrome modeled on it.

Last month, the NIMH Pediatric Developmental Neuroscience Branch convened dozens of experts from the field — including prominent PANDAS critics — to update the science and attempt to achieve consensus on criteria defining the syndrome. The mere fact that the conference took place signals a change in the scientific climate. Until now, whether a child presenting with sudden onset of OCD and/or tic symptoms gets checked for possible involvement of strep has varied—often depending on which medical journals a practitioner happens to read. I am hopeful that will begin to change in light of the new evidence.

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Impetus for the July conference came, in part, from publication of two independent studies within the past year that lend new credence to the PANDAS concept.

In the first, Columbia University researchers demonstrated, for the first time, that strep-triggered antibodies alone are necessary and sufficient to trigger a PANDAS-like syndrome in mice.4 In an autoimmune-disease susceptible strain of mice, exposure to strep triggered OCD-like repetitive behaviors and antibodies that attacked specific molecules in the brain. PANDAS-like behaviors also emerged in naïve mice after they received antibodies from such PANDAS mice. These included impaired learning and memory and social interaction. As in humans with PANDAS, these impairments were more common in males than females.

In the second study, a Yale University research team reported that OCD and Tourette Syndrome (tic) symptoms worsened slightly following a strep infection in some affected children. Moreover, the strep infection triggered the worsened symptoms by increasing the impact of psycho-social stress.5 The findings suggest that a subset of children with these disorders may be at increased risk of strep infection, which could interact with stress to exacerbate the course, as is seen in other infectious and autoimmune diseases.

MORE at http://www.nimh.nih.gov/about/director/index-ocd.shtml">NIMH