Study Evaluating The Safety, Tolerability And Brain Function Of 2 Doses Of PF-0254920 In Subjects With Early Huntington's Disease

• Drug: PF-02545920
  
  • Dose will be titrated up every 2 days by 5mg increments: 5mg Days 1-2, 10mg days 3-4, 15mg days 5-6, and reach 20 mg from Days 7 to Day28.
  • Orally, approx. Q12H (range 10-14 hours), administered at least one hour prior to, or two hours after meals.
  • Treatment for 28 days.
• Drug: Placebo
  

  - Orally, approx. Q12H (range 10-14 hours), administered at least one hour prior to, or two hours after meals.

  Dosing for 28 days.

• Drug: PF-02545920
  
  • 5mg dose
  • Orally, approx. Q12H (range 10-14 hours), administered at least one hour prior to, or two hours after meals.
  • Dosing for 28 days.
• Drug: Placebo
  
  • Orally, approx. Q12H (range 10-14 hours), administered at least one hour prior to, or two hours after meals.
  • Dosing for 28 days.

• Experimental: 20 mg Arm Cohort A
  
  Intervention: Drug: PF-02545920
• Placebo Comparator: Placebo Arm Cohort A
  
  Intervention: Drug: Placebo
• Experimental: 5 mg Arm Cohort B
  
  Intervention: Drug: PF-02545920
• Placebo Comparator: Placebo Arm Cohort B
  
  Intervention: Drug: Placebo

Inclusion Criteria:

• Must have a diagnosis of Huntington's Disease
• a CAG repeat expansion equal or great than 39
• a Unified Huntington Disease Rating Scale (UHDRS) Total Motor Score equal or greater than 5 and less than 60
• a UHDRS Total Functional Capacity equal or greater than 9

Exclusion Criteria:

• Subjects with evidence or history of severe acute or chronic medical condition or laboratory abnormality, or significant neurological disorder other than HD.
• Treatment with any antipsychotic medication within 5 weeks of enrollment