Brain volume loss ‘not accelerated in bipolar disorder’
MedWire News: Bipolar disorder patients do not have accelerated prefrontal gyrification index (GI) loss, but having at least one brain-derived neurotrophic factor (BDNF) gene variant may increase loss, UK scientists have found.
Brain structural abnormalities, including temporal lobe and prefrontal cortex volume reductions, have been identified in bipolar disorder patients. However, it is not clear whether the abnormalities are present at disease onset or whether they develop over time.
Noting that the BDNF valine (val)66methionine (met) variant has been linked to such brain changes, Ajay Mirakur and colleagues from the University of Edinburgh performed magnetic resonance imaging (MRI) at baseline and after 4 years in 18 bipolar I disorder patients and 18 healthy controls.
The GI was calculated as the ratio of folded inner contour to exposed outer contour. In addition, the participants underwent clinical assessment and were genotyped for BDNF val66met.
Both bipolar disorder patients and healthy controls were found to have a significant decrease in GI over 4 years in all prefrontal quadrants, and there was no significant difference in the rate of change of GI between patients and controls.
Comparing bipolar disorder patients with and without at least one BDNF val66met met allele, the team discovered that having at least one met allele was associated with a significantly increased change in GI over 4 years in all four prefrontal quadrants, but particularly in the right dorsal prefrontal cortex.
Carriers of a met allele were significantly older than val/val homozygotes, at 43.9 years versus 35.1 years. When taking age into account, there was a trend toward a significant difference in change in GI between met carriers and val/val homozygotes in the ventral quadrants, and a significant difference in dorsal quadrants.
The researchers conclude in the journal Biological Psychiatry: “We show that GI decreases significantly over time and that the rate of change in GI is not different in bipolar patients compared with control subjects but is accelerated in bipolar participants possessing at least one BDNF allele.
“These findings suggest that GI is not purely a neurodevelopmental measure and raise the possibility that GI may be a sensitive measure of morphological change with time.”
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By Liam Davenport