This is a single site, open-label study designed to examine dopamine transporter density using [123I]β-CIT SPECT imaging before and following treatment with IRX4204 for a 30-day period in early Parkinson's disease patients. In addition, clinical evaluations will be performed to evaluate the effect of IRX4204 treatment on the motor and cognitive symptoms of PD.

Fifteen patients with early PD were enrolled in this open label study, in 3 cohorts of 5 patients each, treated with IRX4204 at 5 mg/day, 10mg/day, or 20 mg/day. Patients were administered IRX4204 orally once daily. Baseline assessments were performed for total motor score, and Unified Parkinson's Disease Rating Scale (UPDRS). Follow-up assessments of these clinical outcome measures were performed at 14 and 29 days of treatment. [123]β-CIT SPECT imaging for assessment of dopamine active transporter (DAT) expression was performed at baseline, and on day 30 of IRX4204 treatment. Patients had clinical hematology and chemistry laboratory tests, and recording of adverse events, performed at baseline and at follow up visits.

Inclusion Criteria:

1. Participant is 40-80 years of age, inclusive.

2. Participant has a clinical diagnosis of PD based on the UK Brain Bank Criteria.

3. Participant has Hoehn and Yahr stage < 3.

4. Participant may be treated with PD symptomatic therapy on a stable dose for at least 30 days prior to the Screening Visit. Dose levels of PD symptomatic therapies will remain stable through the patient's participation in the study, unless a change of dose level is indicated because of adverse events.

5. Participant must be willing and able to provide informed consent.

6. Females must be of either non-child bearing potential based on:

   • post-menopausal for at least 2 years, or
   • surgically sterilized If of child bearing potential, must be neither pregnant or breastfeeding at Screening, and must be willing to avoid pregnancy by using medically accepted contraception (use of an intrauterine device or use of a double barrier method when engaging in sexual intercourse with a male partner) for 4 weeks prior to and 4 weeks following the last dose of study medication.

Exclusion Criteria:

1. Has any form of parkinsonism other than idiopathic PD
2. Are currently experiencing motor fluctuations (end of dose wearing off or dyskinesias) reflective of later stage PD
3. Has evidence of dementia or significant cognitive dysfunction
4. Has clinically significant abnormal laboratory value and/or clinically significant unstable medical or psychiatric illness.
5. The subject has any disorder that may interfere with drug absorption, distribution, metabolism or excretion.
6. The subject has evidence of clinically significant gastrointestinal, cardiovascular, hepatic, renal, hematological, neoplastic, endocrine, alternative neurological, immunodeficiency, pulmonary, or other disorder or disease.
7. Pregnancy or breastfeeding