PROFIL Study to Investigate the Effect of GPB on NfL Levels in Patients With Corticobasal Syndrome (CBS)

Inclusion Criteria:

1. Age: ≥ 18 years

2. "clinical possible" or "clinical probable" CBS (Armstrong et al., Neurol-ogy, 2013 80;496-503) and patients with Progressive Supranuclear Palsy-CBS according toHöglinger et al. (Mov Disord. 2017 Jun;32(6):853-864)

3. No regular consumption of glycerol phenylbutyrate within the last 6 months prior toV1

4. Capable of thoroughly understanding all information given and giving full informedconsent according to GCP

5. Capability and willingness to comply with the procedures of the clinical trial

6. Women of childbearing age must be non-lactating and surgically sterile or using ahighly effective method of birth control and have a nega-tive pregnancy test. Incase of using a hormonal contraception, the method must be supplemented with abarrier method (preferably male condom). Acceptable methods of birth control with alow failure rate i.e. less than 1% per year when used consistently and correct aresuch as implants, injectables, combined oral contraceptives, hormonal intrauterinedevices (IUDs), sexual abstinence (defined as refraining from heterosexualintercourse during the clinical trial) or vasectomized partner. Unacceptable birthcontrol methods are: periodic abstinence (calendar, symptothermal, post-ovulationmethods), withdrawal (coitus interruptus), spermicides only and lactationalamenorrhoea method (LAM). Female condom and male condom should not be used together.

7. A stable regimen for at least 1 month prior to V1 and no foreseeable need to changethe regimen throughout the 26 week treatment period for

8. drugs acting against Parkinsonism (e.g. Levodopa, Dopamine-Agonists, Amantadineand MAO-B-Inhibitors)

9. other CNS-active substances including e.g. antidepressants and antidementiadrugs

Exclusion Criteria:

1. Neurodegenerative diseases other than CBS

2. Underlying Alzheimer's pathology as defined by positive β-amyloid-PET or reduced Aβ 1-42 in CSF

3. Participation in another clinical trial involving administration of aninvestigational medicinal product within 1 month or 5 half-lives of theinvestigational medicinal product, whichever is longer, prior to V1

4. Known hypersensitivity to glycerol phenylbutyrate or its further components, or todrugs with a similar chemical structure or to any of the components of the placebo

5. Treatment with valproic acid, haloperidol or probenecid

6. A physical or psychiatric condition (e.g. frontal lobe syndrome, psychotic disorderor major depression), which at the investigator's discretion may put the subject atrisk, may confound the trial results or may interfere with the subject'sparticipation in this clinical trial

7. Persistent abuse of medication, drugs or alcohol

8. Current or planned pregnancy or breast-feeding in females

9. Other severe medical conditions upon the discretion of the investigator