A young man presenting with recurrent nephrolithiasis

A male patient, born in 1990, first presented with a kidney stone when he was 10 years old, but the stone had passed spontaneously, and no further testing was done at that time. At the age of 20, he presented with a second episode of renal colic. Proteinuria and microscopic haematuria were also noticed, for which he was referred to a nephrologist. On examination, he was a lean young man with normal height and stature. Height was 175 cm, and weight was 59 kg. Systemic examination was unremarkable. Blood pressure was 107/74 mmHg. Laboratory examination showed an elevated serum creatinine of 130 μmol/L (1.44 mg/dL) (eGFR 62 mL/min/ 1.73 m). Serum alkaline phosphatase level was 122 U/L with elevated bone fraction of alkaline phosphatase. Other blood tests were normal. Twenty-four-hour urine collection showed proteinuria of 2.981 g/day consisting mainly of low-molecular-weight proteins. Calciuria was 8.3 mmol/ day (334 mg/day) or 5.7 mg/kg/day (normal <4). Urine sediment analysis was normal (Table 1). Ultrasonography, CT scan and MRI revealed normal kidney size and contour but bilateral multiple cysts. The cysts were mainly localized in the cortex, and they had a benign simple appearance. Furthermore, bilateral nephrolithiasis and intraparenchymal calcification consistent with nephrocalcinosis were seen (Figures 1 and 2). Renal biopsy had been performed in another centre and had shown normal light microscopy, normal electron microscopy, and negative immunofluorescence. After the acute renal colic, transurethral stone extraction was performed. Stone analysis showed a stone consisting of calcium phosphate and calcium oxalate. Family history was negative for renal disease or renal colic. The patient had no siblings. The parents underwent a renal ultrasound examination: both had normal morphology of their kidneys without cysts, but one asymptomatic nephrolithiasis was found in the father.