Spinocerebellar ataxia type 17 (SCA17): Oculomotor phenotype and clinical characterization of 15 Italian patients

SCA17 is a rare type of autosomal dominant spinocerebellar ataxia caused by a CAG/CAA expansion in the gene encoding the TATA-binding protein (TBP).We screened for triplet expansion in the TBP gene 110 subjects with progressive cerebellar ataxia and 94 subjects with Huntington-like phenotype negative at specific molecular tests. SCA17 mutation-positive subjects were found in both groups of patients. Expanded alleles with ≥ 44 CAG/CAA repeats were identified in 11 individuals and in 4 non-symptomatic relatives. Eleven de novo diagnosed patients and four patients previously reported underwent extensive clinical, neuroradiological and oculographic examination. Cerebellar signs and symptoms were present in all cases; 80% of the patients had mild to severe cognitive deficits; 66% of patients showed choreic movements; pyramidal signs, bradykinesia and dystonia were observed in approx 50% of the cases. MRI demonstrated cortical and cerebellar atrophy in all patients, whereas neurophysiological examination excluded signs of peripheral nervous system involvement. Oculographic examinations were performed in 9 out of 15 patients and showed a distinct pattern of oculomotor abnormalities, characterized by impairment of smooth pursuit, defects in the saccade accuracy, normal saccade velocity, hyperreflexia of vestibuloocular reflexes, and absence of nystagmus.