Bone mineral density and urinary N-acetyl-beta-D-glucosaminidase activity in paediatric patients with idiopathic hypercalciuria.
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.
Skalova
Sylva
S
Department of Paediatrics, Faculty of Medicine, Charles University, Hradec Králové, Czech Republic.
Palicka
Vladimir
V
Kutilek
Stepan
S
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
D000118:Acetylglucosaminidase; D002118:Calcium