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Patients diagnosed with obsessive-compulsive disorder (OCD) are more likely to suffer schizophrenia and other schizophrenia spectrum disorders.

While some studies show that obsessive-compulsive disorder and schizophrenia rarely overlap each other, other studies reveal higher rates of coexisting illness with the two disorders in patients.

Lead researcher Sandra M. Meier, Ph.D., of Aarhus University, Denmark, and colleagues, examined data of 3 million people born between 1955 and 2006 were followed up from 1995 through 2012.

Researchers noted that a total of 16,231 people developed schizophrenia and 447 (2.75 percent) of these people were previously diagnosed with obsessive-compulsive disorder. The study also revealed that a total of 30,556 people developed a schizophrenia spectrum disorder and 700 (2.29 percent) of these people were previously diagnosed with obsessive-compulsive disorder.

Researchers said the latest findings suggest that being diagnosed with obsessive-compulsive disorder significantly increases the risk of developing schizophrenia and schizophrenia spectrum disorders later in life. The findings also suggest that children of people diagnosed with obsessive-compulsive disorder were also significantly more likely to develop schizophrenia and schizophrenia spectrum disorders.

"Despite the fact that our results indicate putative overlapping etiological factors of OCD and schizophrenia or schizophrenia spectrum disorders, they do not necessarily suggest that these disorders should be aggregated into one global diagnosis. However, given these findings and the fact that OCD and schizophrenia co-occur with one another at a higher rate than would be expected in the general population, the phenotypes of these disorders are potentially more similar than currently acknowledged. ... Further research is needed to disentangle which genetic and environmental risk factors are truly common to OCD and schizophrenia or schizophrenia spectrum disorders," researchers wrote in the study.

The findings were published September 3 in the journal JAMA Psychiatry.