Adenine phosphoribosyltransferase deficiency

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Adenine phosphoribosyltransferase (APRT) deficiency is an inherited condition that affects the kidneys and urinary tract. The most common feature of this condition is recurrent kidney stones; urinary tract stones are also a frequent symptom. Kidney and urinary tract stones can create blockages in the urinary tract, causing pain during urination and difficulty releasing urine.

Affected individuals can develop features of this condition anytime from infancy to late adulthood. When the condition appears in infancy, the first sign is usually the presence of tiny grains of reddish-brown material in the baby's diaper caused by the passing of stones. Later, recurrent kidney and urinary tract stones can lead to problems with kidney function beginning as early as mid- to late childhood. Approximately half of individuals with APRT deficiency first experience signs and symptoms of the condition in adulthood. The first features in affected adults are usually kidney stones and related urinary problems. Other signs and symptoms of APRT deficiency caused by kidney and urinary tract stones include fever, urinary tract infection, blood in the urine (hematuria), abdominal cramps, nausea, and vomiting.

Without treatment, kidney function can decline, which may lead to end-stage renal disease (ESRD). ESRD is a life-threatening failure of kidney function that occurs when the kidneys are no longer able to filter fluids and waste products from the body effectively.

The features of this condition and their severity vary greatly among affected individuals, even among members of the same family. It is estimated that 15 to 20 percent of people with APRT deficiency do not have any signs or symptoms of the condition.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Mutations in the APRT gene cause APRT deficiency. This gene provides instructions for making APRT, an enzyme that helps to convert a DNA building block (nucleotide) called adenine to a molecule called adenosine monophosphate (AMP). This conversion occurs when AMP is needed as a source of energy for cells.

APRT gene mutations lead to the production of an abnormal APRT enzyme with reduced function or prevent the production of any enzyme. A lack of functional enzyme impairs the conversion of adenine to AMP. As a result, adenine is converted to another molecule called 2,8-dihydroxyadenine (2,8-DHA). 2,8-DHA crystallizes in urine, forming stones in the kidneys and urinary tract. 2,8-DHA crystals are brownish in color, which explains why affected infants frequently have dark urine stains in their diapers. 2,8-DHA is toxic to kidneys, which may explain the possible decline in kidney function and the progression to ESRD.

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

APRT deficiency is estimated to affect 1 in 27,000 people in Japan. The condition is rarer in Europe, where it is thought to affect 1 in 50,000 to 100,000 people. The prevalence of APRT deficiency outside these populations is unknown.

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.

Abnormal enzyme/coenzyme activity · Very frequent (99-80%)

Concentration or activity of an enzyme is above or below the limits of normal in the blood circulation.

Acute kidney injury · Frequent (79-30%)

Sudden loss of renal function, as manifested by decreased urine production, and a rise in serum creatinine or blood urea nitrogen concentration (azotemia).

Chronic kidney disease · Frequent (79-30%)

Functional anomaly of the kidney persisting for at least three months.

Dysuria · Frequent (79-30%)

Painful or difficult urination.

Hypertension · Frequent (79-30%)

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

Nephrolithiasis · Frequent (79-30%)

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

Proteinuria · Frequent (79-30%)

Increased levels of protein in the urine.

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.

Other findings in the same source

From: Orphanet

Additional reported features include Abdominal colic (Occasional (29-5%)); Atrial fibrillation (Occasional (29-5%)); Flank pain (Occasional (29-5%)); Macroscopic hematuria (Occasional (29-5%)); Oliguria (Occasional (29-5%)); Recurrent urinary tract infections (Occasional (29-5%)); Stage 5 chronic kidney disease (Occasional (29-5%)); Uric acid nephrolithiasis (Occasional (29-5%)); Urinary hesitancy (Occasional (29-5%)); Urinary retention (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 Adenine phosphoribosyltransferase deficiency 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

Where the source describes treatments, these are an overview of possible care, not a prescription for an individual. Ask which option applies to the confirmed diagnosis, what benefit is expected, what adverse effects to watch for and how progress will be assessed. Availability, approvals and local practice can differ from the country described in the source.

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.