Open Label Extension Study To Investigate Long Term Safety, Tolerability And Efficacy Of Pf-02545920 In Subjects With Huntington's Disease Who Completed Study A8241021

This study is a 12 month open label extension study of PF-02545920 20 mg dosed BID following
study A8241021 in subjects with HD. Primary endpoints will be to assess long-term safety and
tolerability of 20 mg BID of PF-02545920. Secondary endpoints will be the change from
baseline in the Total Motor Score (TMS)assessment, and/ior the Total maximum Chorea (TMC)
assessment of the Unified Huntington Disease Rating Scale (UHDRS) after 6 and 12 months of
treatment, and Clinical Global Impression-Improvement score after 6 and 12 months of
treatment. Subjects, who were assigned to the 20 mg PF-02545920 dose group in the preceding
A8241021 study, will receive 20 mg PF-02545920 without any titration. All other subjects will
be titrated to the 20 mg BID dose as follows: 5 mg BID for 7 days, 10 mg BID for 7 days, 15
mg BID for 7 days, then 20 mg BID for the remainder of the treatment phase. Up to 260
subjects may take part in this open label extension