DECT Study in Allopurinol-Treated Gout Patients

DECT is a technique that enables visualization of MSU crystal deposits by analysis of the
chemical composition of the scanned materials. This study will determine the extent of MSU
crystal volume in the hands/wrists, feet/ankles, and knees as determined by DECT of subjects
with gout taking a dose of at least 300 mg allopurinol daily for the past 12 weeks.

Patients with gout on allopurinol with and without tophi to be assessed using DECT imaging
for crystal deposition with assessments, which include patient and provider assessments of
disease severity and pain, prior to and after the scan.

Inclusion Criteria:

- Subject is able to understand the study procedures, the risks involved and willing to
provide written informed consent before the first study related activity.

- Subject is willing to adhere to the visit/protocol schedules.

- Subject meets the diagnosis of gout as per the American Rheumatism Association
Criteria for the Classification of Acute Arthritis of Primary Gout.

- Subject has been taking allopurinol at a dose of at least 300 mg daily for at least
12 weeks prior to Day 1, as the sole uratelowering therapy.

Exclusion Criteria:

- Subject who is pregnant or breastfeeding.

- Subject with any other medical or psychological condition, which in the opinion of
the Investigator and/or Medical Monitor, might create undue risk to the subject or
interfere with the subject's ability to comply with the protocol requirements
(including dual energy computed tomography imaging), or to complete the study.

- Subject who has received an investigational therapy or has participated in any
clinical trial or research study within 30 days of Day 1.

- Subject who has taken pegloticase (KRYSTEXXA®) or is expected to take pegloticase
during the study.