Introduction

Spinocerebellar ataxia (SCA) type 1 and 2 are the autosomal dominant neurodegenerative disorders. These are the common subtypes of SCA worldwide and caused by unstable CAG trinucleotide repeat expansion at ATXN1 and ATXN2 genes for SCA type1 and 2 respectively. Cortical and subcortical atrophies (especially cerebellar) are well known in these SCAs by previous neuroimaging studies1, but very little known about the differential default mode connectivity. The use of functional connectivity (FC) measurements is a powerful tool that helps in the discrimination of neurodegenerative diseases. To know the connectivity in SCA type 1 and 2, we have studied default mode network by using resting state fMRI. Additionally, we have also explored the differential loss of volume of brain areas in the same patient groups by structural MRI.

Methods

The resting state fMRI (180 dynamics) and 3D T1-weighted data were acquired using a 3T scanner (Achieva, M/s Philips Medical Systems, The Netherlands) and analyzed using conn toolbox (SPM12) in genetically proven SCA1 (n =9 , age = 35.9 ± 7.6 years) and SCA2 (n =9 , age = 30.9 ± 7.6 years) patients. ROI to ROI based analysis (p<0.05, FDR corrected) was used. While the 3D T1-weighted scans of the whole brain was analyzed by FreeSurfer (version 5.3) software in the same patient groups. MRI parameters used in T1-weighted scans were: Voxel size = 0.6×0.6×1, FOV = 240×240×180 and flip angle = 8ᵒ.

Results

We found the subcortical loss of volume in medulla, pons, brainstem, left cerebellar cortex and right cerebellar cortex in SCA2 than SCA1 patients (table 1). Interestingly, a positive functional connectivity was observed in anterior cerebellum and precuneus (T =4.340; p = 0.042) and post cingulate cortex (T = 4.390; p = 0.042) in SCA1 patients in comparison to SCA2 patients.

Conclusion

On the structural volumetric analysis, the cerebellar and brainstem neurodegeneration have been found to be more in SCA2 as compared with SCA1 patients. Also, the default mode network analysis may differentiate SCA type1 and 2 using fMRI. The negative connectivity in SCA2 may be attributed to the impairment in saccadic subsystem efficient for vision. The role of precuneus in spatial vision2 and posterior cingulate cortex in cognition3,4 help to understand an alternate connectivity in these patients.

Acknowledgements

No acknowledgement found.

References

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