To characterize the phenotypic presentations of spinocerebellar ataxia, type 8.

Spinocerebellar ataxia type 8 (SCA8) is caused by a trinucleotide repeat expansion in one of two overlapping genes on chromosome 13q21: CTG in the 3’ untranslated region of the ATXN8OS gene or CAG in the ATXN8 gene. Repeat length over 80 is often pathogenic, but there is incomplete penetrance. Classically, patients present with gait, limb, speech, and oculomotor incoordination, spasticity, and sensory loss. However, there is wide variability in phenotypic presentations.

The three cases of SCA8 differed significantly from one another.  Patient 1 developed head tremor, which progressed to include bilateral action and postural appendicular tremor with myoclonic features and gait ataxia. MRI of the brain showed chronic microvascular disease, and there was a family history of tremor. Patient 2 had progressive gait ataxia and dysarthria with slowed saccades, nystagmus, restricted up-gaze, executive dysfunction and parkinsonism at presentation. MRI brain showed midbrain and cerebellar atrophy, and there was no relevant family history. Patient 3 initially presented with postural tremor, then developed parkinsonism, cognitive impairment, and restricted extraocular movements. MRI brain also showed chronic microvascular changes, and there was a family history of ataxia. All patients were diagnosed with a comprehensive ataxia panel including SCA evaluation. These cases differ from the classic presentation of SCA8 and reflect the array of features reported in the literature.

SCA8 is known for its phenotypic variability. We present the largest video case series of SCA8 patients that highlights the different clinical presentations, family history, and imaging findings. Improving accessibility to genetic ataxia panels increases the capability of diagnosing a diverse and rare condition.