<s>[INST] <<SYS>> This is a medical question of type : frequency <</SYS>> How many people are affected by spinocerebellar ataxia type 3 ? [/INST] The prevalence of SCA3 is unknown. This condition is thought to be the most common type of spinocerebellar ataxia; however, all types of spinocerebellar ataxia are relatively rare. </s>