For example, two of the four lines of mice that are null for the Prion protein genePrnp, exhibited late onset ataxia and neurodegeneration -- this was subsequently found to be the result of aberrant upregulation of a gene (Prnd) downstream ofPrnp, which occurred as a result of induced exon skipping (Mooreet al., 1999). This evidence concerns the gene PRND and cerebellar ataxia.