Calcium oxalate (CaOx) crystal deposition within the tubules is often a perplexing finding on renal biopsy of both native and transplanted kidneys. Understanding the underlying causes may help diagnosis and future management. The most frequent cause of CaOx crystal deposition within the kidney is hyperoxaluria. When this is seen in native kidney biopsy, primary hyperoxaluria must be considered and investigated further with biochemical and genetic tests. Secondary hyperoxaluria, for example due to enteric hyperoxaluria following bariatric surgery, ingested ethylene glycol or vitamin C overdose may also cause CaOx deposition in native kidneys. CaOx deposition is a frequent finding in renal transplant biopsy, often as a consequence of acute tubular necrosis and is associated with poorer long-term graft outcomes. CaOx crystal deposition in the renal transplant may also be secondary to any of the causes associated with this phenotype in the native kidney. The pathophysiology underlying CaOx deposition is complex but this histological phenotype may indicate serious underlying pathology and should always warrant further investigation.
IntroductionThe genetics underlying the idiopathic hypercalciuria leading to calciumcontaining renal stones remains elusive. The discovery of rare monogenic tubulopathies, often leading to hypercalciuria, has increased our understanding of tubular physiology and patho-physiology. However, insights into idiopathic calcium stone formation have not been gained from these disorders. The aim of this study is to examine CYP24A1 mutations in cohorts of patients with calcium nephrolithiasis.
Materials and MethodsWe examined two cohorts of stoneforming patients for mutations in CYP24A1, which encodes the vitamin D24-hydroxylase enzyme. The first cohort had a biochemical phenotype of suppressed parathyroid hormone and high normal serum calcium, whilst the second cohort had a hypercalciuria phenotype. We did not identify bi-allelic sequence variants in CYP24A1 in our cohorts.
ResultsIn cohort 1, we identified 9 known sequence variants. In cohort 2 we identified 7 known sequence variants. Conclusion CYP24A1 mutations remain a rare cause of calcium nephrolithiasis and hypercalciuria.
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