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People who are left-handed are more likely to develop psychotic disorders like schizophrenia rather than mood disorders such as depression, new research shows.

About 10 percent of the US population is left-handed. A new study that compares all patients with mental disorders, shows that 11 percent of those diagnosed with mood disorders such as depression and bipolar disorder are left-handed—which is similar to the rate in the general population.

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But “a striking of 40 percent of those with schizophrenia or schizoaffective disorder are left-handed,” says Jadon Webb, a child and adolescent psychiatry fellow at the Yale University Child Study Center, who has a particular interest in biomarkers of psychosis.

“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 says.

Tailored treatment

“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.”

For the study, published in the journal SAGE Open, Webb and colleagues studied 107 individuals from a public outpatient psychiatric clinic seeking treatment in an urban, low-income community.

The researchers determined the frequency of left-handedness within the group of patients identified with different types of mental disorders.

The study shows that white patients with psychotic illness are more likely to be left-handed than black patients. “Even after controlling for this, however, a large difference between psychotic and mood disorder patients remained,” Webb says.

Keep it simple

What sets this study apart from other handedness research is the simplicity of the questionnaire and analysis. Patients who were attending their usual check-ups at the mental health facility were simply asked “What hand do you write with?”

“This told us much of what we needed to know in a very simple, practical way,” Webb says. “Doing a simple analysis meant that there were no obstacles to participating and we had a very high participation rate of 97 percent.

“Patients dealing with serious symptoms of psychosis might have had a harder time participating in a more complicated set of questions or tests.

“By keeping the survey simple, we were able to get an accurate snapshot of a hard-to-study subgroup of mentally ill people—those who are often poverty-stricken with very poor family and community support.”

Source: Yale University