Primary hyperoxaluria

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Primary hyperoxaluria is a rare condition characterized by recurrent kidney and bladder stones. The condition often results in end stage renal disease (ESRD), which is a life-threatening condition that prevents the kidneys from filtering fluids and waste products from the body effectively.

Primary hyperoxaluria results from the overproduction of a substance called oxalate. Oxalate is filtered through the kidneys and excreted as a waste product in urine, leading to abnormally high levels of this substance in urine (hyperoxaluria). During its excretion, oxalate can combine with calcium to form calcium oxalate, a hard compound that is the main component of kidney and bladder stones. Deposits of calcium oxalate can damage the kidneys and other organs and lead to blood in the urine (hematuria), urinary tract infections, kidney damage, ESRD, and injury to other organs. Over time, kidney function decreases such that the kidneys can no longer excrete as much oxalate as they receive. As a result oxalate levels in the blood rise, and the substance gets deposited in tissues throughout the body (systemic oxalosis), particularly in bones and the walls of blood vessels. Oxalosis in bones can cause fractures.

There are three types of primary hyperoxaluria that differ in their severity and genetic cause. In primary hyperoxaluria type 1, kidney stones typically begin to appear anytime from childhood to early adulthood, and ESRD can develop at any age. Primary hyperoxaluria type 2 is similar to type 1, but ESRD develops later in life. In primary hyperoxaluria type 3, affected individuals often develop kidney stones in early childhood, but few cases of this type have been described so additional signs and symptoms of this type are unclear.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Mutations in the AGXT, GRHPR, and HOGA1 genes cause primary hyperoxaluria types 1, 2, and 3, respectively. These genes provide instructions for making enzymes that are involved in the breakdown and processing of protein building blocks (amino acids) and other compounds. The enzyme produced from the HOGA1 gene is involved in the breakdown of an amino acid, which results in the formation of a compound called glyoxylate. This compound is further broken down by the enzymes produced from the AGXT and GRHPR genes.

Mutations in the AGXT, GRHPR, or HOGA1 gene lead to a decrease in production or activity of the respective proteins, which prevents the normal breakdown of glyoxylate. AGXT and GRHPR gene mutations result in an accumulation of glyoxylate, which is then converted to oxalate for removal from the body as a waste product. HOGA1 gene mutations also result in excess oxalate, although researchers are unsure as to how this occurs. Oxalate that is not excreted from the body combines with calcium to form calcium oxalate deposits, which can damage the kidneys and other organs.

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

Primary hyperoxaluria is estimated to affect 1 in 58,000 individuals worldwide. Type 1 is the most common form, accounting for approximately 80 percent of cases. Types 2 and 3 each account for about 10 percent of cases.

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.

Calcium oxalate nephrolithiasis · Very frequent (99-80%)

The presence of calcium- and oxalate-containing calculi (stones) in the kidneys.

Hyperoxaluria · Very frequent (99-80%)

Increased excretion of oxalates in the urine.

Abnormality of the dental pulp · Frequent (79-30%)

An abnormality of the dental pulp.

Abnormality of the dentition · Frequent (79-30%)

Any abnormality of the teeth.

Aciduria · Frequent (79-30%)

Excretion of urine with an acid pH, i.e., having an increased hydrogen ion concentration.

Arterial occlusion · Frequent (79-30%)

Blockage of blood flow through an artery.

Bone pain · Frequent (79-30%)

An unpleasant sensation characterized by physical discomfort (such as pricking, throbbing, or aching) localized to bone.

Choroidal neovascularization · Frequent (79-30%)

Choroidal neovascularization (CNV) is the inward growth of new blood vessels arising from the choriocapillaris. Depending on the stage of development, they can be external (type 1 NV) or internal (type 2 NV) to the retinal pigment epithelium.

Other findings in the same source

From: Orphanet

Additional reported features include Chronic kidney disease (Frequent (79-30%)); Elevated circulating hepatic transaminase concentration (Frequent (79-30%)); Elevated urine glycolate (Frequent (79-30%)); Failure to thrive (Frequent (79-30%)); Gangrene (Frequent (79-30%)); Generalized osteosclerosis (Frequent (79-30%)); Heart block (Frequent (79-30%)); Hematuria (Frequent (79-30%)); Intermittent claudication (Frequent (79-30%)); Metabolic acidosis (Frequent (79-30%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Primary hyperoxaluria 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 Primary hyperoxaluria. 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.

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.