Accelerated loss of prefrontal gyrification in bipolar disorder is linked to having at least one brain-derived neurotropgic factor (BDNF) variant, although the overall rate is no higher in such patients, say UK researchers.

Studies have shown that there are structural cerebral abnormalities in bipolar disorder patients, but it is not clear whether they are present at disease-onset or develop over time. As a measure of brain morphology, the gyrification index (GI) of cortical folding has been found to be increased in patients with acute schizophrenia and decreased in those with chronic schizophrenia.

To examine GI changes in bipolar disorder, Ajay Mirakhur and colleagues, from the University of Edinburgh, performed magnetic resonance imaging at baseline and after 4 years in 18 bipolar I disorder patients and 18 healthy controls. They calculated prefrontal GI as the ratio of folded inner contour to exposed outer contour.

Both bipolar disorder patients and healthy controls had a significant decrease in GI over 4 years for dorsal and ventral prefrontal quadrants bilaterally, with no significant difference in the rate of change between patients and controls.

The team also found that bipolar disorder patients with at least one BDNF val⁶⁶met met allele experienced a significantly increased change in GI, particularly in the right dorsal prefrontal cortex, compared with patients with no copies of the BDNF val⁶⁶met met allele, with, GIs at baseline and at follow-up of 2.48 versus 2.31 and 2.47 versus 2.42, respectively.

Interestingly, the team notes in the journal Biological Psychiatry that carriers of the met allele were significantly older than non-carriers, at 43.9 years versus 35.1 years. After taking age into account, the associations between the met allele and change in GI were significant only in the dorsal quadrants. Taking into account medications had no effect on the findings.

“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,” the researchers conclude.

MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a part of Springer Science+Business Media. © Current Medicine Group Ltd; 2009

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