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Hyperoxaluria – Causes, Symptoms & Treatment

Hyperoxaluria is a metabolic disorder characterized by elevated levels of oxalate in the urine, which can lead to kidney stones and serious kidney damage.

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Hyperoxaluria is a metabolic disorder characterized by elevated levels of oxalate in the urine, which can lead to kidney stones and serious kidney damage.

What is Hyperoxaluria?

Hyperoxaluria is a metabolic disorder in which the body excretes abnormally high levels of oxalate – a byproduct of various metabolic processes – through the urine. Oxalate is an organic compound that is produced naturally in the body or absorbed from food. When oxalate concentrations in the urine become too high, it can combine with calcium to form insoluble calcium oxalate crystals, leading to kidney stones (nephrolithiasis) and, over time, serious kidney damage.

Causes and Types

There are two main forms of hyperoxaluria: primary and secondary hyperoxaluria.

Primary Hyperoxaluria (PH)

Primary hyperoxaluria is a rare, genetically inherited condition in which liver enzymes responsible for metabolizing oxalate are absent or dysfunctional. Three distinct types are recognized:

Type 1 (PH1): Caused by a deficiency of the enzyme alanine-glyoxylate aminotransferase (AGT) in the liver. This is the most common and most severe form.
Type 2 (PH2): Results from a deficiency of the enzyme glyoxylate reductase/hydroxypyruvate reductase (GRHPR).
Type 3 (PH3): Caused by a mutation in the HOGA1 gene, which encodes the enzyme 4-hydroxy-2-oxoglutarate aldolase.

Secondary Hyperoxaluria

Secondary hyperoxaluria develops due to external factors and is far more common than the primary form. Common causes include:

Excessive dietary intake of oxalate-rich foods (e.g., spinach, rhubarb, nuts, chocolate)
Gastrointestinal conditions such as Crohn's disease, celiac disease, or short bowel syndrome, which increase oxalate absorption in the intestine (enteric hyperoxaluria)
Low dietary calcium intake, as calcium normally binds oxalate in the gut and prevents its absorption
Chronic vitamin B6 deficiency
Certain medications or bariatric procedures (e.g., gastric bypass surgery)

Symptoms

Symptoms of hyperoxaluria vary depending on the severity of the condition and the amount of oxalate excreted. Common signs include:

Recurrent kidney stones (nephrolithiasis), often occurring in childhood or adolescence in primary forms
Severe back or flank pain (renal colic)
Blood in the urine (hematuria)
Frequent urinary tract infections
In severe cases: kidney failure or end-stage renal disease
Deposits of calcium oxalate in other organs (oxalosis), such as bones, the heart, or the eyes – particularly in primary hyperoxaluria type 1

Diagnosis

Diagnosis of hyperoxaluria involves several investigations:

24-hour urine analysis: Measurement of urinary oxalate over 24 hours (normal value: less than 0.5 mmol/day in adults)
Blood tests: Assessment of plasma oxalate levels and creatinine to evaluate kidney function
Imaging studies: Ultrasound or CT scan of the kidneys to detect stones or calcifications
Genetic testing: To identify the causative gene mutation when primary hyperoxaluria is suspected
Liver biopsy: In specific cases to measure enzyme activity (primarily for PH1)

Treatment

Treatment depends on the underlying cause and the severity of the condition.

General Measures

High fluid intake (at least 2–3 liters per day) to dilute urine and prevent crystal formation
Low-oxalate diet: Reducing consumption of spinach, rhubarb, nuts, cocoa, and other high-oxalate foods
Adequate dietary calcium intake (binds oxalate in the intestine)

Medical Therapy

Alkali citrates (e.g., potassium citrate): Raise urinary pH and inhibit calcium oxalate crystallization
Vitamin B6 (pyridoxine): Can significantly reduce oxalate production in some patients with PH1
Lumasiran: A novel RNA interference medication (approved for PH1) that reduces oxalate production in the liver

Severe Cases

Dialysis: In cases of kidney failure to remove oxalate from the blood
Combined liver-kidney transplantation: For primary hyperoxaluria type 1 with advanced renal failure, as kidney transplantation alone is insufficient without correcting the enzymatic defect in the liver

References

Hoppe B. - An update on primary hyperoxaluria. Nature Reviews Nephrology, 2012; 8(8): 467–475. (PubMed)
Knauf F., Asplin J.R. - Hyperoxaluria: Causes and treatments. Urologic Clinics of North America, 2019; 46(2): 161–170.
Orphanet – Primary Hyperoxaluria. Available at: www.orpha.net (accessed 2024)

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