Altered corpus callosum microstructure in people with non-syndromic congenital mirror movements (CMM)

• Micro-organization of the corpus callosum was different in people with congenital mirror movements (CMM) compared to controls. • Reduced fractional anisotropy (FA) values were found in motor and premotor callosal connections of the CMM group. • Unpredicted group differences in occipital portions of the corpus callosum were also found. Our aim is to define the microstructural organization of the corpus callosum (CC) in people with congenital mirror movements (CMM). We hypothesised that smaller fractional anisotropy (FA) values will be found in our CMM sample compared to the control group. Diffusion tractography (DTI) was applied to quantify CC microstructure in 46 neurologically-normal controls and four individuals with CMM characterised by pathogenic variants known to interact with netrin-1 during embryonic development of axonal pathfinding processes. FA was quantified across 80 nodes within each of 8 predefined CC fibre tracts. FA was smaller in our CMM sample in hypothesised premotor-motor regions of the CC and portions of high axonal density of CC-occipital regions. Microstructural effects differentiating our CMM sample and Controls point to the etiology of CMM and possibly also neurocompensatory effects, particularly in relation to occipital CC regions; the latter remains to be fully investigated in future work. This study provides insights into CC micro-organisation and identifies specific regions of the CC that differ from normal in individuals with non-syndromic CMM. Findings potentially also inform knowledge about the broader range of neurological and neuropsychological disorders involving abnormalities of the CC.