Results of a study suggest that schizophrenia may be associated with a larger range of autoimmune diseases than previously suspected.

Schizophrenia affects about 1 percent of the population and can trigger delusions, paranoia, and hallucinations. It is very difficult to treat. A few autoimmune disorders are thought to play some role in schizophrenia.

Dr. William W. Eaton, of the Johns Hopkins University, Baltimore, and colleagues examined the association between schizophrenia and a range of autoimmune diseases using three databases.

Included in the analysis were 7704 subjects diagnosed with schizophrenia between 1981 and 1998 and their parents, and age- and sex-matched controls and their parents.

Subjects with a history of one or more autoimmune diseases had a 45 percent higher risk of schizophrenia, according to the authors. Schizophrenia patients had a higher prevalence of nine autoimmune disorders compared with comparison subjects.

Compared with the parents of controls, the parents of schizophrenic patients had a higher prevalence of 12 autoimmune diseases.

The autoimmune disorders - thyrotoxicosis, celiac disease, acquired hemolytic anemia, Interstitial cystitis, and Sjogren’s syndrome - occurred more often in schizophrenic patients and their parents compared with the controls and their parents.

“In future clinical studies, it may be interesting to search for a family history of autoimmune diseases ... in patients with schizophrenia,” Eaton’s team suggests. “Eventually, individual or family disease comorbidity may help to elucidate shared etiologic pathways.”

SOURCE: American Journal of Psychiatry March 2006.