Brain Structure and Degeneration Staging in Friedreich Ataxia: MRI Volumetrics from the ENIGMA-Ataxia Working Group

This group of investigators undertook a comprehensive characterization of the spatial profile and progressive evolution of structural brain abnormalities in people with FRDA. A coordinated international analysis of regional brain volume using magnetic resonance imaging data charted the whole-brain profile, inter-individual variability, and temporal staging of structural brain differences in 248 individuals with FRDA and 262 healthy controls. The brainstem, dentate nucleus region, and superior and inferior cerebellar peduncles showed greatest reductions in volume relative to controls (Cohen's d = 1.5-2.6). Cerebellar grey matter alterations were most pronounced in lobules I-VI (d = 0.8), while cerebral differences occurred most prominently in precentral gyri (d = 0.6) and corticospinal tracts (d = 1.4). Earlier onset age predicted less volume in the motor cerebellum (rmax = 0.35) and peduncles (rmax = 0.36). Disease duration and severity correlated with volume deficits in the dentate nucleus region, brainstem, and superior/inferior cerebellar peduncles (rmax = -0.49); subgrouping showed these to be robust and early features of FRDA, and strong candidates for further biomarker validation. Cerebral white matter abnormalities, particularly in corticospinal pathways, emerge as intermediate disease features. Cerebellar and cerebral grey matter loss, principally targeting motor and sensory systems, preferentially manifests later in the disease course. FRDA is defined by an evolving spatial profile of neuroanatomical changes beyond primary pathology in the cerebellum and spinal cord, in line with its progressive clinical course. The design, interpretation, and generalization of research studies and clinical trials must consider neuroanatomical staging and associated inter-individual variability in brain measures.

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