Fronto-cerebellar connectivity disruptions and functional reorganization in Friedreich's Ataxia: A structural and...

Friedreich's ataxia (FRDA) is an inherited neurodegenerative disorder characterized by progressive ataxia and multisystem manifestations resulting from involvement of the peripheral and central nervous systems. While regional atrophy is known to be associated with symptoms, functional network alterations may represent a critical pathological mechanism; however, their specific contribution to motor and cognitive impairment remains unclear. We combined T1-weighted anatomical MRI and resting-state functional MRI (rs-fMRI) in 37 individuals with FRDA and 41 age- and sex-matched healthy controls and explored how functional connectivity differences are related to atrophy, clinical severity and cognitive performance. Regional volumes were quantified using morphometry analyses, spontaneous rs-fMRI activity was assessed via amplitudes of low-frequency fluctuations, and functional co-activation was evaluated among regions showing structural and neuronal activity alterations. Volume reductions were most pronounced in the brainstem, cerebellar white matter, hemisphere of lobules VI, X, and thalamus. Functionally, individuals with FRDA showed decreased fronto-cerebellar connectivity alongside increased intracerebellar, thalamo-striatal, and hippocampal-cerebellar coupling. Infratentorial and thalamic volume loss correlated strongly with clinical disease severity, whereas reduced frontal co-activation with cerebellar lobules VI, Crus I and II was moderately associated with poorer motor and cognitive performance. In contrast, increased intracerebellar and hippocampal-cerebellar coupling was observed particularly in individuals with more advanced disease and was partly associated with better cognitive outcomes. These findings indicate widespread disruptions of long-range cerebro-cerebellar connectivity together with increased intraregional coupling and potential network reorganization, underscoring the importance of network-level mechanisms for understanding clinical heterogeneity in FRDA and guiding future prognostic and therapeutic studies.