This mutant protein was chosen for evaluation because it is known to be a cause of spinocerebellar ataxia in humans74, which is an outcome of disabling mutations in CA8. Similar results are observed in agar diffusion assays (Fig. 4c), again demonstrating that the WT CA8 protein modestly increases guanidine-induced reporter gene expression, whereas the mutant protein does not. The gene discussed is CA8; the disease is cerebellar ataxia.