Cystinuria

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Cystinuria is a condition characterized by the buildup of the amino acid cystine, a building block of most proteins, in the kidneys and bladder. As the kidneys filter blood to create urine, cystine is normally absorbed back into the bloodstream. People with cystinuria cannot properly reabsorb cystine into their bloodstream, so the amino acid accumulates in their urine.

As urine becomes more concentrated in the kidneys, the excess cystine forms crystals. Larger crystals become stones that may lodge in the kidneys or in the bladder. Sometimes cystine crystals combine with calcium molecules in the kidneys to form large stones. These crystals and stones can create blockages in the urinary tract and reduce the ability of the kidneys to eliminate waste through urine. The stones also provide sites where bacteria may cause infections.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Mutations in the SLC3A1 or SLC7A9 gene cause cystinuria. The SLC3A1 and SLC7A9 genes provide instructions for making the two parts (subunits) of a protein complex that is primarily found in the kidneys. Normally this protein complex controls the reabsorption of certain amino acids, including cystine, into the blood from the filtered fluid that will become urine. Mutations in either the SLC3A1 gene or SLC7A9 gene disrupt the ability of the protein complex to reabsorb amino acids, which causes the amino acids to become concentrated in the urine. As the levels of cystine in the urine increase, the crystals typical of cystinuria form. The other amino acids that are reabsorbed by the protein complex do not create crystals when they accumulate in the urine.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

Cystinuria affects approximately 1 in 10,000 people.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Abnormality of amino acid metabolism · Very frequent (99-80%)

Abnormality of an amino acid metabolic process.

Cystinuria · Very frequent (99-80%)

An increased concentration of cystine in the urine.

Hematuria · Very frequent (99-80%)

The presence of blood in the urine. Hematuria may be gross hematuria (visible to the naked eye) or microscopic hematuria (detected by dipstick or microscopic examination of the urine).

Nephrolithiasis · Very frequent (99-80%)

Kidney stones (calculi) are mineral concretions in the renal calyces and pelvis that are found free or attached to the renal papillae.

Abnormal urinary odor · Frequent (79-30%)

A deviation from the normal odor of the urine.

Flank pain · Frequent (79-30%)

An unpleasant sensation characterized by physical discomfort (such as pricking, throbbing, or aching) and perceived to originate in the flank.

Hypertension · Frequent (79-30%)

The presence of chronic increased pressure in the systemic arterial system.

Hyperuricemia · Frequent (79-30%)

The concentration of uric acid in the blood circulation is above the upper limit of normal.

Hypocitraturia · Frequent (79-30%)

A lower than normal concentration of citrate(3-) in the urine.

Nausea and vomiting · Frequent (79-30%)

Nausea is a commonly encountered symptom that has been defined as an unpleasant painless subjective feeling that one will imminently vomit. Vomiting has been defined as the forceful expulsion of the contents of the stomach, duodenum, or jejunum through the oral cavity. While nausea and vomiting are often thought to exist on a temporal continuum, this is not always the case. There are situations when severe nausea may be present without emesis and less frequently, when emesis may be present without preceding nausea.

Renal insufficiency · Frequent (79-30%)

A reduction in the level of performance of the kidneys in areas of function comprising the concentration of urine, removal of wastes, the maintenance of electrolyte balance, homeostasis of blood pressure, and calcium metabolism.

Cystine crystalluria · Frequent (79-30%)

Echogenic fetal colon · Occasional (29-5%)

A type of echogenic fetal bowel in which the hyperechogenicity is strictly limited to the colon.

Hyperuricosuria · Occasional (29-5%)

An abnormally high level of uric acid in the urine.

Other findings in the same source

From: Orphanet

Additional reported features include Hypercalciuria (Occasional (29-5%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Cystinuria is Nephrology, with a nephrologist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• How is kidney function being assessed over time?
• Are any current medicines or supplements relevant to kidney safety?
• Is there an individual recommendation about fluids, diet or blood pressure?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Cystinuria. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.