ATXN1 and cerebellar ataxia: However, some subtypes of hereditary cerebellar ataxia and spastic ataxia, such as spinocerebellar ataxia (SCA) type 1 (ATXN1) (10) and type 3 (ATXN3) (11) and Friedreich's ataxia (FXN) (12), have been reported to present as isolated spastic paraplegia and are caused by abnormal trinucleotide repeat (TNR) expansion.