Cystine Capacity Clinical Study (CysCap)

Study Overview
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Brief Summary
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The purpose of this study is to determine whether urinary cystine capacity, an assay used to measure the amount of cystine in the urine, can be used to predict stone recurrence in patients with cystinuria.

Detailed Description
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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.

Official Title
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Cystine Capacity Clinical Study (CysCap)

Conditions
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Cystinuria

Participation Criteria
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Eligibility Criteria
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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.

Ages Eligible for Study
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Minimum Age: 8 Years
Maximum Age: 80 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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No

Study Plan
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How is the study designed?
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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Cystinuria<br> | |

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Cystine capacity will be correlated with recurrence or non-recurrence of stones | The primary end point will be cystine capacity in participants who do and do not have recurrence of stones seen on radiologic imaging in the ipsilateral kidney which was rendered stone-free prior to enrollment. Subjects who are enrolled in the study will perform semi-annual 24-hour urine collections for measurement of cystine capacity. 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. | every 6 months over 3 years | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| 24-hour urine cystine excretion | We will compare 24 hour urine cystine excretion in patients who remain stone free and those who experience stone recurrence. | every 6 months over 3 years | 
| episodes of renal colic and/or stone passage from a kidney that was previously stone-free | Assessed by renal imaging, either ultrasound or CT scan, every 6 months. | every 6 months over 3 years | 
| Evidence of new asymptomatic stones noted on the contralateral kidney | Cystine capacity will be compared in participants with or without recurrence of stones in the contralateral kidney by renal ultrasound or CT scan | every 6 months over 3 year observational study | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Renal aminoaciduria, cystinuria, D-penicillamine, renal tubular transport, inborn errors, tiopronin, urolithiasis