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19-09-2011 | Mental health | Article

Corpus callosum alterations in BD ‘linked to disease not genetics’


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MedWire News: Corpus callosum (CC) abnormalities in patients with bipolar disorder (BD) appear to be disease related, rather than reflecting a genetic vulnerability to the illness, a US study of twins suggests.

"As the largest white matter fiber tract in the brain, the CC is a critical component of the biological infrastructure that allows communication among brain regions," explain Carrie Bearden (University of California, Los Angeles) and team.

They add that CC "volume reduction has been observed in patients with BD, but whether these deficits reflect genetic vulnerability to the illness remains unresolved."

To investigate further, the researchers studied 21 individuals (48% women) with bipolar I disorder, aged a mean of 44.4 years, 19 of their unaffected co-twins, and 34 mentally healthy control twins. The three groups were similar in terms of age, education, handedness, and gender.

All of the participants underwent magnetic resonance imaging, which revealed no significant differences among the three groups regarding total brain volume.

However, post hoc pairwise contrasts revealed that BD patients had a significantly reduced callosal area compared with their co-twins, while there were no significant differences between co-twins and control twins.

Maps of callosal thickness revealed significant localized thinning in BD patients relative to co-twins and control twins, particularly in the genu and splenium. Again, there were no significant differences between co-twins and control twins in callosal thickness.

The researchers also found that BD patients showed significantly altered CC curvature compared with their co-twins and controls twins, with no significant differences between the latter two groups.

In BD patients and their co-twins, callosal reductions in the genu and splenium were significantly associated with measures of cognitive processing speed (verbal fluency) and response inhibition.

There were no significant association between medication use and CC measurements in the BD patients, the researchers note.

Bearden et al conclude in the journal Cerebral Cortex: "We found evidence for structural alteration in the CC associated with bipolar illness, which appeared to be a disease-specific, rather than genetically mediated, effect."

They add: "Our findings further implicate disrupted interhemispheric connectivity in bipolar disorder. Further studies are needed to determine the etiology of callosal alterations and when in the course of illness they develop."

MedWire ( is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2010

By Mark Cowen

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