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MR neuroimaging and proton spectroscopy in Wolfram syndrome
Stefania Evangelisti1,2, Chiara La Morgia1,3, Claudia Testa1,2, David Neil Manners1,2, Claudio Bianchini1,2, Michele Carbonelli3, Giulia Amore1, Alessandra Maresca1, Leonardo Caporali1, Raffaele Lodi1,2, Valerio Carelli1,3, and Caterina Tonon1,2

1Department of Biomedical and NeuroMotor Sciences, University of Bologna, Bologna, Italy, 2Functional MR Unit, Policlinico S.Orsola - Malpighi, Bologna, Italy, 3IRCCS Institute of Neurological Sciences of Bologna, Bologna, Italy

Synopsis

We characterized neurodegeneration in Wolfram syndrome by combining MR neuroimaging and proton MRS, and evaluated pathological accumulation of brain lactate as a. mitochondrial oxidative impairment marker. Cerebellar white matter loss was widespread, while grey matter loss was stronger within sensorimotor and cognitive cerebellar lobules. Infratentorial neurodegeneration was confirmed by biochemical signs of neuro-axonal degeneration in cerebellum and pons. The lack of abnormal ventricle lactate suggests an absence of dysfunction of mitochondrial metabolism. These morphological, microstructural and biochemical alterations were in line with neuropathological findings of loss of myelinated axons in the visual system, smaller brainstem and cerebellar white matter loss.

Introduction

Wolfram syndrome (WS) is a rare (1 in ~770000)1 progressive autosomal recessive genetic disease, characterized by early childhood onset of the combination of insulin dependent diabetes mellitus, optic nerve atrophy, diabetes insipidus and deafness. Neurologic abnormalities (cerebellar ataxia, brainstem dysfunction and epilepsy) are also present from the early stages1. The neurodegeneration pattern of this disorder has been characterised by few in vivo neuroimaging studies: decrease grey matter (GM) volume and white matter (WM) microstructural alterations were found mainly in the brainstem, cerebellum and optic radiations1,2. Changes in mitochondrial dynamics were observed in relation to a deficiency of WFS1 (protein Wolfram syndrome 1) and mitochondrial morphological and biochemical changes were detected at muscle biopsy3,4,5. The aim of this study was to further characterize Wolfram syndrome neurodegeneration, by combining MR neuroimaging and proton MRS, and evaluate pathological brain accumulation of lactate as a potential mitochondrial oxidative impairment marker.

Methods

Ten patients with confirmed WFS1 gene mutations, who underwent brain MR in their diagnostic workup, were enrolled. Acquisitions were performed with a 1.5T GE scanner, equipped with a head coil. The standardized MR protocol included volumetric T1-w images (TR/TE/TI=12.5/5.1/600ms, 1mm3 isotropic), diffusion-weighted MRI (TR/TE=10.000/87.5ms, 25-directions, b-value=900 mm2s−1, voxel=1.25x1.25x4mm) and single voxel 1H-MR spectroscopy (PRESS) with localizations in the lateral ventricles (TR/TE=1500/288ms, volume=3.7-8.2ml, NEX=384), left cerebellar hemisphere (TR/TE=4000/35ms, volume=6ml, NEX=64), left parieto-occipital white matter (TR/TE=4000/35ms, volume=8ml, NEX=64) and pons (TR/TE=1500/40ms, volume=1.2-1.5ml, NEX=512)6,7. Not all the patients completed the whole protocol; groups of sex- and age-matched healthy controls were included (Tab.1). Voxel-based morphometry (VBM) analyses were performed on T1-w images using SPM 12.0. Whole-brain VBM was supplemented by software optimized for evaluating infratentorial structures (Spatially Unbiased Infratentorial Toolbox, SUIT8). Morphometric measurements were performed following previously reported methods9,10. Sagittal middle cerebellar peduncle (MCP) diameter, coronal superior cerebellar peduncle (SCP) diameter, pons and midbrain areas, MCP/SCP ratio, pons/midbrain ratio and MR Parkinsonism Index were evaluated. Diffusion-weighted data underwent standard pre-processing and tensor fitting. Voxelwise analysis of tensor parameters was performed using TBSS (Tract-Based Spatial Statistics). Mean Diffusivity (MD) and Fractional Anisotropy (FA) values were also evaluated within manually defined ROIs (listed in Tab.2). To globally evaluate brain DTI parameters, we created MD and FA histograms of cerebral and cerebellar hemispheres, brainstem, vermis and posterior fossa1. Spectra were analysed with LCModel 6.3, and relative metabolites concentrations were evaluated. Group comparisons were performed with univariate analyses (SPSS®); voxelwise comparisons were non-parametric (permutation method). Statistical significance was set to p<0.05 (corrected for multiple comparisons).

Results

Whole-brain VBM showed GM loss in WS in the occipital pole and cerebellum (Fig.1) and WM loss in the corpus callosum, anterior corona radiate, optic radiations, cerebellum and brainstem (Fig.1). Cerebellum-specific VBM showed that WM loss was widespread while GM loss affected the whole cerebellum but with a stronger effect within left lobule VIII, vermis IX, bilateral crus I, II, V, VI. TBSS highlighted lower FA (and higher MD) for patients mainly within optic and thalamic radiations, corpus callosum and cerebellar tracts. These effects were mainly driven by a higher radial diffusivity, while axial diffusivity was unaltered (Fig.2). ROI-based DTI showed altered FA and MD mainly within the posterior fossa, basal ganglia and optic radiations (Tab.2). As for morphometric measures, patients had smaller MCP and SCP diameters, pons and midbrain areas, and a lower pons to midbrain area ratio (Tab.2). Ventricular lactate was absent in 7/10 patients, while traces were present in 3/10 patients. WS patients had lower cerebellar NAA/Cr and NAA/mI concentrations, and higher mI/Cr. Lower NAA/Cr and NAA/mI concentrations were also found in the pons, while no differences were found in the parieto-occipital white matter (Tab.3).

Discussion and conclusions

Whole-brain VBM, TBSS and ROI-based DTI results are in line with previous literature1,2. Considering that all previous advanced neuroimaging studies in Wolfram syndrome report data on about 20 patients in total, this confirmation is significant. The most innovative aspects of this study were the fine-grained characterization of cerebellar neurodegeneration using both biochemical and topographic profiles. In particular, cerebellar VBM demonstrated that WM loss was widespread with analogous extent, while GM loss was stronger within cerebellar lobules involved in sensorimotor and cognitive/behavioural functions12,13. This might be of particular interest taking into account the psychiatric manifestations of Wolfram syndrome described in combination with neurological deficits14. Infratentorial neurodegeneration was also confirmed by biochemical signs of neuro-axonal degeneration in cerebellum and pons. The lack of abnormal ventricular lactate excludes the hypothesis of dysfunction in mitochondrial metabolism. These morphological, microstructural and biochemical alterations of the cerebellum are in line with the neuropathological investigation of two WS patients15,16.

Acknowledgements

No acknowledgement found.

References

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Figures

Table 1. Demographic summary of patients and healthy controls. Subgroups for different MR data are reported. No significant differences in age and sex between patients and controls were found for any subgroup (as assessed with Mann-Whitney and Pearson-c2 respectively). WS: Wolfram syndrome; HC: healthy controls; N: number of participants, M: male, F: female; MRS: Magnetic Resonance Spectroscopy.

Figure 1. Evaluation of tissue loss by VBM group comparison. Top: whole brain GM loss (left) and cerebellar GM loss (right). Bottom: whole brain WM loss (left) and cerebellar WM loss (right). P-values maps (corrected for multiple comparisons) are shown projected onto study-specific templates. Cerebellar VBM results are shown for two different significance thresholds (p<0.05 and p<0.001). WS: Wolfram syndrome patients; HC: healthy controls.

Figure 2. TBSS group comparison results. From left to right FA, MD and RD maps are shown. Axial diffusivity did not shown significant alterations. P-values maps (corrected for multiple comparisons, p<0.05) are reported in red projected onto the group mean FA image and white matter skeleton (in green). FA: fractional anisotropy; MD: mean diffusivity; RD: radial diffusivity; WS: Wolfram syndrome patients; HC: healthy controls.

Table 2. Morphometric analysis and ROI-based DTI results. P-values, group means and standard deviations (sd) are reported for morphometric measures and ROI-based DTI. MD values are in mm2s-1 and with a scaling factor of 10-3. Significant results that survived Bonferroni correction (p=0.0071 for morphometries; p=0.0022 for DTI) are in bold. WS: Wolfram syndrome patients; HC: healthy controls; MCP: middle cerebellar peduncles; SCP: superior cerebellar peduncles. (ROIs: medulla, dentate nucleus, pons, MCP, cerebellar white matter, SCP, midbrain SCPs decussation, posterior limb of internal capsule, thalamus, globus pallidus, putamen, head of caudate, parieto-occipital and pre-frontal white matter, genu and splenium corpus callosum).

Table 3. MRS spectroscopy results. P-values, group means and standard deviations (sd) are reported for the metabolites concentrations that were altered in Wolfram patients within the cerebellar hemisphere and the pons. Significant results that survived Bonferroni correction (p=0.0083) are in bold. No significant differences were found within the parieto-occipital white matter. Lactate was not detected within lateral ventricles (in higher than trace concentrations), for any of the patients, and therefore quantifiable. WS: Wolfram syndrome patients; HC: healthy controls; NAA: N-acetyl-aspartate ; Cr: Creatine; mI: myoinositol.

Proc. Intl. Soc. Mag. Reson. Med. 26 (2018)
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