Liability for schizophrenia linked to cognition in mood disorders

By Mark Cowen

Schizotypal traits and genetic liability for schizophrenia are associated with reduced cognitive functioning in patients with mood disorders, Japanese study results show.

The team found that schizotypy negatively correlated with verbal comprehension in patients with mood disorders, while a family history of schizophrenia in first-degree relatives was associated with poorer performance in all cognitive areas.

"Liability for schizophrenia could play a pivotal role in neurocognitive functioning in mood disorders, suggesting that such liability might lie on a continuum ranging from normality through mood disorders to full-blown schizophrenia," say Hiroaki Hori (National Center of Neurology and Psychiatry, Tokyo) and colleagues.

The findings come from a study of 41 depressed patients with bipolar II disorder (BD II), 131 patients with unipolar major depressive disorder, and 225 age-, gender-, and education-matched mentally healthy individuals (controls).

All of the participants were evaluated for neuropsychological functioning using the Wechsler Memory Scale-Revised, the Wechsler Adult Intelligence Scale-Revised, and the Wisconsin Card Sorting Test.

Schizotypal traits were assessed using the Schizotypal Personality Questionnaire (SPQ), and the mood disorder patients were interviewed about diagnosed schizophrenia in family members.

The team found that both groups of mood disorder patients had significantly poorer performance in tests of verbal and visual memory, working memory, and processing speed than controls. And BD II patients had significantly poorer performance in tests of verbal memory and executive functioning than those with unipolar depression.

Both BD II and unipolar depression patients had significantly higher SPQ scores than controls, at 26.4 and 25.2 versus 13.4, respectively, indicating greater schizotypy. The difference in scores between the two mood disorder groups was not significant.

SPQ scores significantly negatively correlated with verbal comprehension performance in BD II and unipolar depression patients, and with working memory performance and processing speed in controls.

In the mood disorder patients, those with at least one first-degree relative with schizophrenia had significantly poorer performance in all cognitive domains compared with those without such a family history.

Hori and team conclude in the Journal of Affective Disorders: "Future large-scale studies are warranted that take account of the density of family history of mood disorders and/or schizophrenia and investigate the effect of familial aggregation/coaggregation of these distinct disorders on neurocognitive status based on the stratification of the density."

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