BDNF and major depressive disorder: Also in prefrontal brain regions, diffusion tensor magnetic resonance imaging (DTI) has shown increased fractional anisotropy in WM fiber bundles associated with particular genotypes of the neurotrophic tyrosine kinase receptor type 2 (NTRK2), but only in subjects diagnosed with depression [101], while specific polymorphisms of the BDNF gene are associated with detection of WM DTI disturbances in subjects with high depression severity [102,103].