For the diagnosis of osteoporosis, fragility fracture rather than bone mineral density (BMD) is important sign of osteoporosis in both children and adults. I agree with the authors' opinion for diagnosis of osteoporosis in children as follows. The subjects with one of the following criteria; (1) Vertebral fragility compression fracture, (2) fracture and z-score equal or less than -2.0, (3) 2 or more long bone fractures by age 10 years, (4) 3 or more long bone fractures by age 19 years.

Each country or ethnicity is recommended to have their own BMD data and guideline for diagnosis and treatment of osteoporosis not only in adults but also in children. For example, clinical practice guideline for bone health in Korean children and adolescents has been published [2]. Korean normative data for children BMD are available for lumbar spine, femoral neck, total body, total body less head areas [3,4].

The authors may need to correct or clarify the adult dosages of the bisphosphonates in the Table 1. Osteoporosis treatment dose of intravenous pamidronate in adult is usually 30–90 mg per every 3–4 months (90 mg every 4 weeks is usually cancer bone metastasis osteolysis treatment dose) [5]. Osteoporosis treatment dose of oral alendronate in adult is 70 mg/wk (not 35 mg/wk) [6].