Background: X-linked hypophosphatemic rickets (XLH) is caused by inactivating mutations in the phosphate-regulating gene with homologies to endopeptidases on the X chromosome (PHEX). In this group of patients, data about renal calcifying disorders are scarce.
Objective and hypotheses: To determine the prevalence of nephrocalcinosis and nephrolithiasis and their risk factors in XLH patients.
Method: 36 patients (15 children and 21 adults; 27 women and nine men) with confirmed PHEX mutations were followed for 5 years at regular intervals. Associated metabolic factors were evaluated by 24-h urinary samples. Blinded radiologists performed renal ultrasonography (US) and computed tomography (CT) and graded nephrocalcinosis using a 03 scale with 0 meaning no nephrocalcinosis and 3 meaning severe nephrocalcinosis. The NC confirmation was determined with a positive result in both US and CT while the NL diagnosis was confirmed by CT.
Results: Besides hyperphosphaturia, present in all XLH patients, hypocitraturia was the most common metabolic factor found (30.5%), while hypercalciuria occurred in two patients (5.5%) and no one had hyperoxaluria. US diagnosed NC in 34 (94.4%) patients: 33 (97%) as grade 1 and one (3%) as grade 2. Meanwhile, CT identified medullary NC in 15 (41.6%) patients: 10 (66.7%) as grade 1 and five (33.3%) as grade 2. CT identified NL in 4 (11.1%) adults. Stratification by age showed a higher prevalence of NC in children than adults (60% vs 28.5%). The pediatric group, in intensive use of phosphate, started treatment earlier (P<0.01) and presented a greater phosphaturia than the adult group (P<0.01).
Conclusion: In our cohort, nephrocalcinosis was more prevalent than nephrolithiasis. The main metabolic factor was hyperphosphaturia and intensive phosphate treatment appears to be a mitigating factor to kidney calcifications.
01 - 03 Oct 2015
European Society for Paediatric Endocrinology