The CYP24A1 gene encodes 1,25-hydroxyvitamin-D 3 -24-hydroxylase, a key enzyme responsible for the catabolism of active vitamin D (1,25-dihydroxyvitamin D 3 ). Loss-offunction mutations in CYP24A1 lead to increased levels of active vitamin D metabolites. Clinically, two distinct phenotypes have been recognised from this: infants with CYP24A1 mutations present with infantile idiopathic hypercalcaemia, often precipitated by prophylactic vitamin D supplementation. A separate phenotype of nephrolithiasis, hypercalciuria and nephrocalcinosis often presents in adulthood. CYP24A1 mutations should be suspected when a classical biochemical profile of high active vitamin D metabolites, high or normal serum calcium, high urine calcium and low parathyroid hormone is detected. Successful treatment with fluconazole, a P450 enzyme inhibitor, has been shown to be effective in individuals with CYP24A1 mutations. Although CYP24A1 mutations are rare, early recognition can prompt definitive diagnosis and ensure treatment is commenced.
Here we define precision medicine approaches and discuss how these may be applied to renal stone-formers to optimise diagnosis and a management. Using the gene discovery of monogenic stone disorders as examples, we discuss the benefits of personalising therapies for renal stone-formers to provide improved prevention and treatment of these disorders.
SUMMARYWe present the case of a 68-year-old man admitted to hospital with severe acute kidney injury secondary to statin-induced rhabdomyolysis. Five weeks previously, the patient started a course of clarithromycin for infection of a finger wound with Mycobacterium marinum. His current medications included simvastatin, which he continued along with clarithromycin. The severity of the acute kidney injury necessitated initial continuous venovenous haemofiltration followed by 12 haemodialysis sessions before a spontaneous improvement in renal function occurred. Statins are widely prescribed and we report this case to encourage increased vigilance in avoiding drug interactions known to increase the risk of statin-induced myopathy, including macrolide antibiotics, calcium channel antagonists and amiodarone. The authors would also like to highlight recent guidance on atorvastatin as the statin of choice in patients with chronic kidney disease, and of the need for dose adjustment in those with an estimated glomerular filtration rate less than 30 mLs/min/1.73 m².
BACKGROUND
Cystinuria is a rare inherited renal stone disease. Mutations in two genes SLC3A1 and SLC7A9 underlie this condition, encoding proteins that facilitate dibasic amino acid exchange which are expressed in the gut and the proximal tubule of the kidney. Genetic studies now allow precise genotyping of patients who may have both autosomal dominant and autosomal recessive patterns of disease. The disorder is characterised by the urinary loss of cystine, lysine, ornithine, and arginine, and the insolubility of cystine gives rise to crystalluria and cysteine-containing renal stones. Although an inherited condition, it may present at any age. Clinical management combines lifestyle advice and preventative medical therapy. However, many patients require surgical interventions to remove problematic stones from the urinary tract. Preventative therapies include increased fluid intake, alkalinization of the urine, and the use of cystine-binding drugs, including penicillamine and tiopronin, which form soluble heterodimers with cystine.
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