Pseudoxanthoma elasticum and nephrolithiasis

We report the case of a 42-year-old man with pseudoxanthoma elasticum (PXE) and recurrent bilateral nephrolithiasis. Diagnosis of PXE was made by yellow papules on the neck and ophthalmologic angioid streaks. This diagnosis was confirmed by a skin biopsy (Von Kossa stain) and by genotyping analysis of ABCC6 (homozygous mutation R1138Q). Nephrolithiasis was recurrent and biological investigations showed hypophosphoraemia, hyperphosphaturia, hypercalciuria, normocalcaemia, normal serum parathyroid hormone value, high 1,25-dihydroxy vitamin D value and a renal calcium oxalate stone. ABCC6 encodes for MRP6, a multidrug resistant protein strongly expressed in the liver and kidney. The substrates of the MRP6 remain unknown. As PXE is characterized by calcification of elastic fibres and this patient presents important phosphocalcic anomalies, we discuss the possible implications of MRP6 in the phosphocalcic metabolism.