Through PCR analysis, followed by Sanger sequencing and high performance capillary electrophoresis (HPCE), we confirmed that the expansion of an unstable CAG tract in exon 10 of the ATXN3 was a causal mutation for the disease called Machado–Joseph Disease (MJD), a type of spinocerebellar ataxia (type 3, SCA3). Here, ATXN3 is linked to cerebellar ataxia.