There is strong qualitative and quantitative evidence of white matter abnormalities in schizophrenia and bipolar disorder from structural magnetic resonance imaging (MRI). There is also good evidence of altered connectivity in schizophrenia using diffusion tensor magnetic resonance imaging, but no study has yet addressed the diagnostic specificity of these findings or whether they are related to specific susceptibility genes.
Diffusion tensor MRI was used to assess white matter integrity in patients with bipolar I disorder (BD) (n=42), schizophrenia (n=28) and healthy controls (n=38). Clinically stable patients with one other close family member with the same diagnosis were selected. In a second study, we examined white matter associations with Neuregulin I in a sample of healthy controls. Fractional anisotropy (FA) was compared between the groups using voxel-based morphometry, automated region of interest analysis and probabilistic tractography. Results : Patients with BD and those with schizophrenia showed reduced FA in the anterior limb of the internal capsule, anterior thalamic radiation and uncinate fasciculus compared with controls. Results from the second study showed reductions in those carrying a Neuregulin 1 variant previously associated with psychotic symptoms.
Reduced white matter density and integrity is common to both schizophrenia and BD. It is likely that this shared white matter disruption is determined in part by shared genetic risk factors.