Sequence‐dependent and independent inhibition specific for mutant ataxin‐3 by small interfering RNA

Abstract
In Machado–Joseph disease (MJD) gene, there is a C/G polymorphism immediately after the CAG repeat; the expanded CAG repeat tract is exclusively followed by C, whereas about half of wild‐type alleles are followed by G. Using this C/G polymorphism, we have engineered the small interfering RNA (siRNA) which decreased the expression of mutant ataxin‐3, Q79C, by 96.0%, whereas there was minimal reduction on that of the wild type, Q22G (5.9%). Furthermore, unexpectedly, the expression of another wild‐type allele, Q22C, was also much less suppressed (22.5%) by this siRNA possibly due to difference of the secondary structure of the target RNA. This is the first report of sequence‐independent discrimination of mutant and wild‐type alleles by siRNA. Ann Neurol 2004;56:124–129