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Lesch-Nyhan syndrome (LNS) is a rare X-linked disease caused by a deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT). This deficiency results in a defect in purine recycling, leading to the accumulation of urate crystals in joints and the urinary tract, causing kidney stones. Other clinical features include neurological impairment, cognitive dysfunction, and self-injurious behavior.
Urate-lowering therapies are used to manage the disease. However, an excessive reduction in uric acid levels can lead to the accumulation of xanthine, an alkaloid with low solubility in urine. This is a rare cause of kidney stones and was first reported in LNS patients in 2018.
Case report
Case Presentation
We present the case of a 30-year-old male patient with LNS who has experienced recurrent nephrolithiasis since the age of 20. Most of the stones were composed of xanthine, others of uric acid. In August 2022, after two episodes of renal colic, bilateral JJ stents were inserted due to hydronephrosis. One year later, the right stent was replaced because of stent calcification and the development of a large stone in the right renal pelvis. After the stent's removal, we analyzed it and the lithiasic formation, using Fourier-transform infrared spectroscopy (FTIR), and found xanthine in both the stent and the stone.
A control CT scan revealed calcification also of the left stent (image). It was subsequently changed, and the right stent was removed, showing early calcification after only one month after its placement.
Ten days after the removal of the right stent, the patient was readmitted for right III-grade hydroureteronephrosis with a 25mm calculus in the kidney pelvis, along with a urinary tract infection (UTI). A percutaneous nephrostomy was then inserted.
Blood tests obtained in 2022, before the stent removal showed: MCV 127 fL, creatinine 1.13 mg/dL, uric acid 3.3 mg/dL, while on therapy with febuxostat 80 mg once daily (as he is intolerant to allopurinol), folic acid 5 mg once daily, potassium citrate 3.5g twice daily, and B12 vitamin 1000IU/week. During the clinical assessment in that occasion, considering the low levels of uric acid and clinical history of xanthine kidney stones, we have already decided to reduce reduced the febuxostat therapy to 80 mg once daily on alternate days, to reduce xanthine accumulation.
LNS therapy involves reducing uric acid levels through allopurinol or febuxostat. Excessive therapy, as previously reported in a few case reports, can result in xanthine kidney stones. Here, we present the first case of xanthine incrustation of JJ stents associated with high-dose febuxostat therapy. This case underscores the importance of carefully titrating urate-lowering therapy in these patients.