Cystine Capacity Clinical Study (CysCap)

Cystinuria is a rare genetic cause of kidney stones that leads to significant morbidity due
to the recurrent nature of the disease. Despite recent advancements in knowledge about
cystinuria, such as the discovery of the genetic defects that cause the disease, there have
been very few studies of clinical determinants of recurrent stone formation. An optimal
method of measuring cystine solubility in the urine has been lacking, and therefore response
to pharmacologic and dietary therapy is often not known. Recently, a new assay to measure the
amount of cystine in the urine was developed called Cystine Capacity, or CysCap. It is an
assay that adds a pre-formed amount of cystine crystals to urine and measures the amount of
cystine the urine can take up from the solid phase (in undersaturated urine) or gives up to
solid phase (in supersaturated urine). This study seeks to examine how well this measure of
urinary cystine predicts stone occurrence, with the ultimate goal of helping to guide therapy
and preventing kidney stones in cystinurics.

This is an observational study over 3 years. Subjects who are enrolled in the study will
perform semi-annual 24-hour urine collections. They will undergo imaging of the kidneys every
6 months to monitor kidney stone formation or growth, in order to correlate urinary
parameters with clinical events. The study will examine how well the urinary cystine capacity
predicts stone formation.

Inclusion Criteria:

- Patients with a confirmed laboratory diagnosis of cystinuria will be included in this
study. There will be no age barrier to inclusion, but included patients must be able
to reliably collect urine for 24 hours. Men and women will be recruited equally and
there are no restrictions for racial or ethnic origin in this study.

- Patient enrollment will require signing of an informed consent document approved by
the Lenox Hill IRB.

- For children 8-18 years of age, signing an assent to participate will also be
required.

Exclusion Criteria:

- Patients will be excluded if they cannot sign consent or assent.

- Furthermore if the patient cannot reliably collect urine for 24 hours or adhere to
study follow up visit requirements.