[Juvenile osteoporosis].

Osteoporosis is induced by a disorder of the bone turnover that generates an accelerated destruction process and leads to the rarefaction of the protein matrix. The RANK-L/RANK/OPG system is the main actor of the bone remodelling regulation. Juvenile osteoporoses may have primary or secondary aetiologies. The main causes include constitutional bone fragilities, and osteoporoses, which are secondary to chronic inflammatory diseases and sustained steroid treatment. Etiologic diagnosis relies on a clinical basis, and is often made too lately when complications occur. Osteodensitometry is a sensitive and noninvasive tool for measuring mineral bone density in children. The reliability of results is limited by the variations due to patients' age, gender, pubertal stage, and by the length of bone pieces. The optimal treatment of osteoporosis is preventive, and includes accurate nutritional diet, D vitamin-calcium supplementation and regular physical activity. Biphosphonates are used for treatment of symptomatic osteoporoses. Careful utilization is required in childhood because their late potential secondary effects are still unknown. New antiresorptive drugs and other that stimulate osteoformation are successfully used in adults. Their effects have not been studied in the paediatric population.