Safety and Tolerability Study of Phenylbutyrate in Huntington's Disease (PHEND-HD)

Inclusion Criteria: * Subjects with clinical diagnosis of HD and family history of HD or a CAG repeat expansion greater than or equal to 37 * Subjects in stage I or II of illness (TFC greater than or equal to 7) * Subjects must be ambulatory and not requiring skilled nursing care * Age of 18 years or older * Women of childbearing potential (i.e., those not postmenopausal or surgically sterile) must confirm to the best of their knowledge that they are not pregnant or plan to get pregnant * Women of childbearing potential must have negative pregnancy test, be non-lactating and use adequate contraception methods, such as oral birth control pills plus a barrier method (i.e. condoms, diaphragm) or IUD during their participation in the study * Subjects currently taking psychotropic medications (including antidepressants and neuroleptics) must be on stable dosages for at least 4 weeks prior to baseline visit and should be maintained on constant dosage throughout the study * Subjects must be capable of providing informed consent and complying with trial procedures * Subjects must be able to take oral medication, a person willing and able to serve as an informant and provide information about the daily dosing of study medication Exclusion Criteria: * Exposure to phenylbutyrate, valproic acid, probenecid, known HDAC inhibitors or other transcriptionally active compounds within 3 months (90 days) prior to the baseline visit * History of known sensitivity or intolerability to phenylbutyrate, sodium butyrate or sodium acetate * Existence of a known malignancy that might require treatment during the course of this study * Exposure to any investigational drug within 30 days of the baseline visit * Subjects with underlying hematologic, hepatic or renal disease; screening white blood cell (WBC) count less than 3,800/mm3, screening creatinine greater than 2.0 or alanine aminotransferase (ALT) greater than 2 times the upper limit of normal * Clinical evidence of unstable medical illness in the investigator's judgment * Clinical illness that requires use of warfarin (Coumadin) * Unstable psychiatric illness defined as psychosis (hallucinations or delusions) untreated major depression or plan for suicide within 90 days of the baseline visit * Current or history of substance (alcohol or drug) abuse within 1 year of the baseline visit * Pregnant women or women who are currently breast-feeding * History of heart failure or other conditions that might be exacerbated by sodium loading