Background: GAA-FGF14 ataxia (SCA27B) is a recently reported late-onset ataxia caused by a GAA repeat expansion in intron 1 of the FGF14 gene. Initial studies revealed cerebellar atrophy in 74-97% of patients. A more detailed brain imaging characterization of GAA-FGF14 ataxia is now needed to provide supportive diagnostic features and earlier disease recognition.
Methods: We performed a retrospective review of the brain MRIs of 35 patients (median age at MRI 63 years; range 28-88 years) from Quebec (n=27), Nancy (n=3), Perth (n=3) and Bengaluru (n=2) to assess the presence of atrophy in vermis, cerebellar hemispheres, brainstem, cerebral hemispheres, and corpus callosum, as well as white matter involvement. Following the identification of the superior cerebellar peduncles (SCPs) involvement, we verified its presence in 54 GAA-FGF14 ataxia patients from four independent cohorts (Tübingen n=29; Donostia n=12; Innsbruck n=7; Cantabria n=6). To assess lobular atrophy, we performed quantitative cerebellar segmentation in 5 affected subjects with available 3D T1-weighted images and matched controls.
Results: Cerebellar atrophy was documented in 33 subjects (94.3%). We observed SCP involvement in 22 subjects (62.8%) and confirmed this finding in 30/54 (55.6%) subjects from the validation cohorts. Cerebellar segmentation showed reduced mean volumes of lobules X and IV in the 5 affected individuals.
Conclusions: Cerebellar atrophy is a key feature of GAA-FGF14 ataxia. The frequent SCP involvement observed in different cohorts may facilitate the diagnosis. The predominant involvement of lobule X correlates with the frequently observed downbeat nystagmus.