We focus on Spinocerebellar ataxia type 1 (SCA1) [95], where suppressors inform on the mechanism of the disease [96,97,98,99], and Rett Syndrome caused by MECP2 deficiency [100], in which N-ethyl-N-nitrosourea (ENU) random mutagenesis screens have yielded novel targets for therapy [101,102,103]. The gene discussed is MECP2; the disease is spinocerebellar ataxia type 1.