For all of the money, energy and focus that has gone into gene studies on schizophrenia, two findings this week call into question much of that effort.

The first one has been widely reported yesterday, Parasite May Lead to Schizophrenia. The parasite? Good ‘ole toxoplasma gondii, a common organism carried by carried by cats and farm animals. In most cases, the parasite is harmless (except for pregnant women, who have long been taught to avoid handling cat litter when pregnant).

But in the latest study, researchers found that 7 percent of people with schizophrenia had this parasite, compared to only 5 percent in people who were not diagnosed with schizophrenia. That puts someone who has this parasite at a 24% increased risk of also getting schizophrenia.

The second study, not yet widely disseminated, found no significant association of 14 candidate genes with schizophrenia. What does this mean? I’ll let the authors speak for themselves:

It is unlikely that common SNPs in these genes account for a substantial proportion of the genetic risk for schizophrenia, although small effects cannot be ruled out.

These 14 genes studied by the researchers do not account for a substantial proportion of the genetic risk for schizophrenia.

This includes many genes previously indicated and believed to have a significant influence on causing schizophrenia. This was a large scale population study (unlike many gene studies), and so its results are fairly robust.

It doesn’t mean genes aren’t a contributing factor to schizophrenia (I’m sure they likely are). Only that, as we’ve noted all along, genes are likely only one tiny part of a complex causative picture for this mental disorder. Third-party factors, like a parasite, seem to also have significant risk impact on the development of schizophrenia.

Dr. John Grohol is the CEO and founder of Psych Central. He is an author, researcher and expert in mental health online, and has been writing about online behavior, mental health and psychology issues -- as well as the intersection of technology and human behavior -- since 1992. Dr. Grohol sits on the editorial board of the journal Cyberpsychology, Behavior and Social Networking and is a founding board member and treasurer of the Society for Participatory Medicine.

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    Last reviewed: By John M. Grohol, Psy.D. on 18 Jan 2008
    Published on PsychCentral.com. All rights reserved.