Left-Handed Patients More Likely to Have Psychotic Disorders

Among those with mental disorders, left-handed patients are more likely to be diagnosed with psychotic conditions like schizophrenia than mood disorders like depression, according to a study published in the October-December 2013 issue of SAGE Open.

For their study, Jadon Webb, MD, of the Yale Child Study Center and researchers from the University of Iowa, the University of Texas Southwestern Medical Center, Georgia Regents University, and the University of California, San Francisco, asked 107 patients seeking treatment for mood and psychiatric disorders to indicate which hand they typically prefer to write with.

While recording the rate of left-handedness within the study population, the authors found that “the prevalence of left-handedness among the mood disorders was close to 10% in our sample, which is similar to the general population average.” But when they examined the prevalence of left-handedness among patients with psychotic illness like schizophrenia or schizoaffective disorder, the authors recorded a highly disproportionate rate of 40%.

“In general, people with psychosis are those who have lost touch with reality in some way, through hallucinations, delusions, or false beliefs, and it is notable that this symptom constellation seems to correlate with being left-handed,” Webb said in a statement.

Among patients suffering from psychosis, Webb and his co-authors also found that white patients were more likely to be left-handed than black patients, though they explained “even after controlling for this, a large difference between psychotic and mood disorder patients remained.”

The researchers noted that previous studies have proposed that the asymmetry of the brain’s left and right hemispheres may cause the correlation, as “variations in development of this asymmetry are suspected to contribute to the pathogenesis of schizophrenia.”

Regardless of the underlying cause, the investigators believe that their findings will assist in the detection of mental disorders.

“Finding biomarkers such as this can hopefully enable us to identify and differentiate mental disorders earlier, and perhaps one day tailor treatment in more effective ways,” Webb concluded.