Does a common parasite increase schizophrenia risk in men? New study finds no link.

Could a parasite many people carry be a hidden trigger for schizophrenia? Researchers looked at this question by comparing men diagnosed with paranoid schizophrenia to healthy men. They tested for antibodies to Toxoplasma gondii—a common parasite often spread by cats—and checked for a specific variation in a gene involved in the immune system. The study found that the men with schizophrenia were no more likely to have the parasite than the healthy men. The immune system gene variation also showed no link to the illness, and there was no sign that the two factors combined to increase risk. This is a clear 'null' result, meaning the study found no evidence for a connection. The findings caution against interpreting a positive test for this parasite in an adult as a biomarker for psychosis risk. The researchers note that future studies should look at whether the timing of infection—like during brain development—might matter more than simply having it as an adult.