HD pathogenesis and somatic instability. (A) We profiled gene expression in striatum and cerebellum in HdhQ 111/111and control (Hdh+/+) mice at 10 weeks of age (GSE19780). Expression values of the 150 instability-correlated probes were used to predict instability indices based on our regression model. Data bars represent mean ± SD (n = 3-5 mice per genotype). (B) Dopamine transporter (DAT) knockout mice were crossed with HdhQ 92mice to test if accelerated HD pathogenesis increases instability (8-10 months, n = 3-4 mice per genotype). Instability indices were measured in striatum and cerebellum. Cerebellum was included as a control tissue that does not show accelerated HD pathology. (C) Hq/+ mice were crossed with HdhQ 111mice to test if pathology in cerebellar granule cells can induce somatic instability (4 months, n = 3 mice per genotype). Instability indices were measured in striatum and cerebellum. Striatum was included as a control tissue that does not show Hq-mediated neurodegeneration. In addition, the Hq mutation did not increase HD CAG instability in cerebellum at either 5 weeks (n = 3-4 per mice genotype) proceeding overt neurodegeneration, or at 7 months (n = 3-4 mice per genotype) when the mice exhibit significant neurodegeneration (data not shown).