Microstructural Alteration of White Matter Tracts due to 16p11.2 Chromosomal Duplication and Deletion
This study aims to characterize microstructural white matter alterations and inter-hemispheric asymmetry that are induced by deletion and duplication at the chromosomal locus 16p11.2, a genetic locus closely associated with neuropsychiatric disorders such as autism spectrum disorder, bipolar disorder, schizophrenia and language disorders (Chang et al., 2016). In order to examine structural alterations of white matter tracts due to copy number variations at the chromosomal locus 16p11.2, diffusion tensors maps, including fractional anisotropy (FA), axial diffusivity (AD) and radial diffusivity (RD), and tract density maps were generated from diffusion-weighted MR images. Our findings indicate that 16p11.2 chromosomal deletion induces systemic increase in AD and FA as well as tract densities in white matter tracts while the duplication at the chromosomal locus 16p11.2 increases RD while decreasing both FA and track density. Interestingly, white matter tracts that were severely affected by 16p11.2 chromosomal deletion and duplication were splenium of corpus callosum (SCC), genu of corpus callosum (GCC) and body of corpus callosum (BCC), all of which are crucial to inter-hemispheric communication of the human brain. These alterations in the microstructures of corpus callosum are thought to significantly contribute to inter-hemispheric asymmetry, which is often an apparent biomarker of many neuropsychiatric and neurodevelopmental disorders. Overall, this study demonstrates the ramification of 16p11.2 chromosomal deletion and duplication on white matter microstructures, and we believe that this relationship between the copy number variations at the chromosomal locus 16p11.2 and the brain structure is a step towards devising and implementing a more efficient and effective interventions and therapies for currently-untreatable neuropsychiatric and neurodevelopmental disorders.