Inclusion Criteria:  Clinical diagnosis of probable progressive supranuclear palsy (PSP) Presence of PSP symptoms for less than 5 years Body weight range of ≥ 41 kg (90 lbs) to ≤ 118 kg (260 lbs) Has a reliable caregiver to accompany the patient to all study visits. Score ≥ 18 on the Mini Mental State Exam (MMSE) at Screening Patient must reside outside a skilled nursing facility or dementia care facility at the time of Screening, and admission to such a facility must not be planned. Residence in an assisted living facility is allowed If patient is receiving coenzyme Q10, levodopa/carbidopa, levodopa/ benserazide, a dopamine agonist, catechol-o-methyltransferase inhibitor, other Parkinson's disease medication, or memantine with or without acetylcholinesterase inhibitors for cognition, the dose must have been stable for at least 30 days prior to Screening and must remain stable for the duration of the study. No such medication may be initiated during the study  Exclusion Criteria:  Patients must not meet any of the following criteria:  Presence of other significant neurological or psychiatric disorders including (but not limited to) Alzheimer's disease; dementia with Lewy bodies; prion disease; Parkinson's disease (which has not subsequently been revised to PSP); amyotrophic lateral sclerosis or other motor neuron disease; multiple sclerosis; any psychotic disorder; severe bipolar or unipolar depression; prior history of a suicide attempt or current suicidal thoughts or behavior that are believed to represent a safety risk as indicated by a "yes" response to Question 2 of the C-SSRS; seizure; brain tumor or other space-occupying lesion; history of stroke; or history of severe head injury within the past 20 years History of significant brain abnormality, including, but not limited to, prior hemorrhage or infarct, cerebral contusion, encephalomalacia, aneurysm, vascular malformation, subdural hematoma (SDH), hydrocephalus, or space-occupying lesion (e.g., abscess or brain tumor such as meningioma). If there is history or evidence on neurologic exam suggesting possible SDH, patients should be fully evaluated, including MRI if indicated, to exclude significant, new SDH Presence of cerebellar ataxia, choreoathetosis, early symptomatic autonomic dysfunction, or moderate to severe resting tremor, responsive to levodopa Known history of serum or plasma progranulin level less than one standard deviation below the normal patient mean for the laboratory performing the assay