HTT and Huntington disease: Puigdellívol et al. (2015) detected a decrease in Rac1 activity in HD-mutant mice (Q7/Q111) (containing alleles with 7 CAG repeats and with targeted insertion of 109 CAG repeats that extends the glutamine segment in huntingtin to 111 residues) in the cortex. Kalirin-7, an activator of Rac1, was found to be significantly reduced in the cortex of these mice. The HdhQ7/Q111 mouse model presented smaller spine density in the motor cortex but not striatum. In addition, the mice were impaired in the ability to learn new motor skills (Puigdellívol et al., 2015).