White Matter Abnormalities Indicate Heredity Nature of Bipolar Disorder

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New evidence has been discovered which helps support the theory that bipolar disorder is a hereditary condition. Researchers have found that widespread white matter integrity reductions in patients with bipolar disorder, which also extends to their unaffected siblings.

Brain Sketch“Together, these results suggest an important role for white matter integrity in the pathology of bipolar disorder and support the validity of white matter integrity as an endophenotype for the illness,” the team writes in The American Journal of Psychiatry.

The researchers used diffusion tensor imaging to find significant reductions in white matter integrity across the whole white-matter skeleton in 64 bipolar disorder patients relative to 46 control participants. The changes correlated with duration of illness, and with Lifetime Dimensions of Psychotic Symptoms scores which suggests that the reductions directly related to the pathology of the illness.

MedwireNews explains the team also looked at specific regions of interest within three categories (limbic and frontotemporal connections, thalamic tracts, and callosal regions) and found that patients had reduced integrity in most of these regions.

Imaging of 60 full siblings of the patients including 54 sibling pairs showed significant reductions in white matter integrity versus controls. Most importantly, these reductions were smaller than those in the patients, and restricted mainly to the splenium of the corpus callosum, the posterior thalamix radiations, and the left superior longitudinal fasciculus.

“These results could reflect a true localization of familial influence in these regions, implying that fractional anisotropy reductions in other areas are determined by illness-specific factors,” say lead study author Emma Sprooten from Yale University School of Medicine.

However, the authors add that it may be easier to detect subtle differences in the “large, well-defined fiber bundles” within these regions.

“Thus, while our results suggest that the familial aspect of fractional anisotropy reductions is restricted to a set of specific tracts, we cannot rule out a more global effect masked by differential sensitivity across the white matter skeleton.”

Seeing that the white matter integrity correlated highly between siblings, which, combined with the relative reductions in unaffected siblings, caused the researchers to believe that a shared set of genes are responsible for white matter abnormalities, as well as the risk for bipolar disorder.

“If so, investigating white matter integrity in molecular and cellular studies may provide new insights into downstream biological pathways and mechanisms of risk genes and may ultimately result in the identification of new medication targets.”

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