What are the causes of nephrocalcinosis?

Causes of Nephrocalcinosis

Nephrocalcinosis results from a diverse array of genetic tubulopathies, metabolic disorders, and iatrogenic factors, with the specific etiology varying significantly by age at presentation and clinical context.

Genetic and Hereditary Causes

Bartter Syndrome Subtypes

• Bartter syndrome types 1 and 2 (BS1, BS2) are the principal inherited disorders presenting with hypercalciuria and nephrocalcinosis in early infancy, typically developing after 1–2 months of life 1, 2
• BS1 results from autosomal-recessive mutations in the SLC12A1 gene (NKCC2 transporter) 2
• BS2 results from autosomal-recessive mutations in the KCNJ1 gene (ROMK/Kir1.1 channel) 2
• Bartter syndrome type 3 (BS3) usually shows normocalciuria but hypercalciuria can occur; some patients exhibit hypocalciuria mimicking Gitelman syndrome 1, 2
• Bartter syndrome types 4a and 4b (BS4) generally have normocalciuria, though hypercalciuria may be present 1, 2
• Transient Bartter syndrome type 5 (BS5) may display hypercalciuria, but nephrocalcinosis is uncommon 1, 2

Other Genetic Tubulopathies

• Familial hypomagnesemia with hypercalciuria and nephrocalcinosis (FHHNC) is caused by mutations in CLDN16 (paracellin-1), leading to urinary magnesium wasting, hypercalciuria, nephrocalcinosis, and progressive renal failure 2
• Dent disease is associated with nephrocalcinosis and has limited supportive therapies, often necessitating early renal replacement 3
• Distal renal tubular acidosis is a common hereditary tubular disorder causing medullary nephrocalcinosis in children 4

Metabolic Genetic Disorders

• Primary hyperoxaluria type 1 (PH1) causes oxalate deposition leading to calcium oxalate nephrocalcinosis, recurrent kidney stones, and chronic kidney disease; characterized by presentation before adolescence, nephrocalcinosis, decreased eGFR at diagnosis, and calcium oxalate monohydrate stone composition 5
• Genotypes affecting vitamin D metabolism and hepatic glyoxylate metabolism are associated with nephrocalcinosis 3

Metabolic and Idiopathic Causes

• Idiopathic hypercalciuria is among the most common causes of medullary nephrocalcinosis in children 4
• Hyperoxaluria (both primary and secondary forms) leads to calcium oxalate deposition 4
• Disorders of vitamin D metabolism can result in nephrocalcinosis 3

Iatrogenic and Acquired Causes

Medication-Related

• Furosemide use is more frequent in preterm infants with nephrocalcinosis 6
• Vitamin D supplementation and intoxication are iatrogenic causes, particularly in newborns 6, 4
• Calcium-containing phosphate binders at dialysate calcium concentration of 1.75 mmol/l are associated with vascular calcification in CKD patients 1

Prematurity-Related

• Hypercalciuria of the premature infant is the main cause in newborns, with multifactorial and largely iatrogenic origins 4
• Bronchopulmonary dysplasia and patent ductus arteriosus are more frequent in preterm infants with nephrocalcinosis 6

Age-Specific Diagnostic Considerations

Prenatal and Neonatal Period

• Polyhydramnios due to excessive fetal polyuria is virtually always caused by Bartter syndrome 1
• Presentation includes renal salt wasting, polyuria, rapid weight loss, dehydration, failure to thrive, recurrent vomiting, and hypochloremic/hypokalemic metabolic alkalosis 1

Full-Term Children and Adolescents

• Full-term children show higher rates of persistent nephrocalcinosis without resolution and chronic kidney disease compared to preterm infants 6
• Monogenic mutation rates are significantly higher in full-term children (OR 10.02,95% CI [2.464-40.786]) 6
• Young age at onset of kidney stone disease should raise suspicion for underlying genetic causes 1

Diagnostic Approach

Initial Evaluation

• Medical history: assess for polyhydramnios, premature birth, growth failure, failure to thrive, recurrent vomiting, and family history 1, 2
• Biochemical parameters: serum electrolytes (Na⁺, Cl⁻, K⁺, Ca²⁺, Mg²⁺), acid-base status, renin, aldosterone, creatinine, fractional excretion of chloride, and urinary calcium-creatinine ratio 1, 2
• Renal ultrasound to detect medullary nephrocalcinosis and kidney stones 1, 2

Genetic Testing Indications

• Offer targeted gene-panel analysis to children and young adults (≤25 years) with nephrolithiasis 2
• Test adults (>25 years) when an inherited or metabolic disorder is suspected 2
• Perform testing for recurrent stone formers (≥2 episodes), bilateral disease, or strong family history 2
• Confirm clinical diagnosis of Bartter syndrome by genetic analysis whenever possible 1
• Analytical sensitivity of Bartter-specific genetic panels is 90–100%; clinical sensitivity is approximately 75% in children but only 12.5% in adults 1, 2

Critical Clinical Pitfalls

• Overlapping phenotypes can mislead diagnosis; BS3 may mimic Gitelman syndrome with hypocalciuria, necessitating genetic confirmation 2
• Large rearrangements in CLCNKB often escape detection by standard next-generation sequencing and require confirmation by multiplex ligation-dependent probe amplification 1, 2
• Primary hyperoxaluria should always be considered in early-onset nephrocalcinosis as it can lead to chronic kidney disease and requires specific investigation 4
• Avoid routine tubular function tests with furosemide or thiazides if genetic testing is accessible, as these carry risk of severe volume depletion in suspected Bartter syndrome 1
• Provide genetic counseling to all families with confirmed pathogenic variants, including cascade screening of relatives 1, 2