title: Bone mineral density and urinary N-acetyl-beta-D-glucosaminidase activity in paediatric patients with idiopathic hypercalciuria.
abstract: BACKGROUND
  Idiopathic hypercalciuria (IH) is defined as hypercalciuria that persists after correction of dietary inbalances and has no detectable causes. Patients with IH have a higher prevalence of osteoporosis. Defective reabsorption of calcium by the renal tubule is considered a likely mechanism of IH. N-acetyl-beta-D-glucosaminidase (NAG) is a lysosomal enzyme that is a very sensitive marker of renal tubular impairment.
  
  
  METHODS
  Fifteen patients (nine boys and six girls, mean age 12.4 +/- 4.0 years) with IH (urinary calcium excretion >0.1 mmol/kg per 24 h) had their bodyweight, height, body mass index (BMI), urinary NAG/creatinine ratio (U-NAG/Cr) and 24-h urinary calcium excretion (U-Ca/24 h) assessed. L1-L4 bone mineral density (BMD) was measured by dual energy X-ray absorptiometry and volumetric BMD (BMDvol) was calculated. The obtained results were expressed as Z-scores.
  
  
  RESULTS
  The values of basic anthropometric parameters did not differ significantly from the values of the reference population and there was a tendency to short stature, which did not reach statistical significance (P = 0.08). The values of calciuria and U-NAG/Cr were significantly higher while BMD was significantly lower when compared to the reference values (P < 0.0006, P < 0.006 and P < 0.001, respectively). Inverse and significant correlations were found between U-Ca/24 h and BMD, U-Ca/24 h and body height, and U-Ca/24 h and BMDvol (r = -0.64 and -0.70, respectively, P < 0.01; r = -0.55, P < 0.05), while there was no correlation between U-NAG/Cr and U-Ca/24 h, nor between BMD and weight or BMD and BMI.
  
  
  CONCLUSIONS
  Tubular impairment is highly probable in children with IH, but there is a poor relationship with the degree of calcium leakage. Idiopathic hypercalciuria should be considered as a risk factor for stunted growth and low bone mass.
authors.affiliation: Department of Paediatrics, Faculty of Medicine, Charles University, Hradec Králové, Czech Republic.
authors.forename: Sylva
authors.initials: S
authors.lastname: Skalova
authors.forename: Vladimir
authors.initials: V
authors.lastname: Palicka
authors.forename: Stepan
authors.initials: S
authors.lastname: Kutilek
mesh_terms: D000118:Acetylglucosaminidase / Q000652:urine*; D000293:Adolescent; D015519:Bone Density; D002118:Calcium / Q000652:urine*; D002128:Calcium Metabolism Disorders / Q000453:epidemiology* / Q000652:urine*; D002648:Child; D005260:Female; D006130:Growth Disorders / Q000453:epidemiology / Q000652:urine; D006801:Humans; D007684:Kidney Tubules / Q000201:enzymology; D008297:Male; D010024:Osteoporosis / Q000453:epidemiology / Q000652:urine; D015995:Prevalence; D012307:Risk Factors
chemical_list: D000118:Acetylglucosaminidase; D002118:Calcium