Abstract Details

SCA 8 is caused by bidirectional transcription at the SCA 8 locus on chromosome 13q21 by way of CAG trinucleotide repeat expansion in the ATXN8 gene or the complementary CTG repeat in the ATXN8OS gene. This leads to slowly progressive neurodegeneration with eye movement abnormalities, progressive cerebellar ataxia, cerebellar atrophy, and pyramidal signs. However, to our knowledge, self-limited seizures have not been previously described in SCA 8. 

To report the natural history of progressive neurodegeneration in a family with 8 out of 9 siblings with Spinocerebellar Ataxia Type 8 (SCA 8).

In this case series, we describe three adult siblings presenting with progressive motor weakness and cognitive decline.  

All patients had history of self-limited epilepsy in infancy, followed by a brief period of normal development. They subsequently had loss of motor and cognitive skills in late childhood-early adolescence.  Family history was notable for 6 (3 males and 3 females) out of 7 siblings with similar clinical phenotype. Father’s progeny including 2 additional children with different mother were also affected, highly suggestive of paternal autosomal dominant inheritance. Examination was significant for nystagmus, impaired smooth pursuit, upper extremity ataxia, spasticity, and inability to ambulate. EMG showed evidence of a demyelinating neuropathy with secondary axonal features. MRI brain demonstrated T1 hyperintensity of decussating fibers of the pons. Genetic testing revealed trinucleotide expansion of ATXN8OS with 99 repeats.  

SCA8 is typically associated with slowly progressive neurologic decline and ataxia in third to fifth decade. However, SCA 8 can have earlier onset as seen in our case series.  Our case series also highlights atypical presentation with self-limited neonatal seizures, not previously described in SCA 8.