This study evaluates bone mineral density (BMD) in pediatric patients aged 5-18 years with conditions negatively affecting bone health, using REMS (Radiofrequency Echographic Multi Spectrometry), a non-invasive and radiation-free ultrasound technology. Bone health is crucial during childhood, when peak bone mass develops, and reduced BMD is associated with increased fracture risk. DXA is the current reference method but has limitations in children, including radiation exposure and growth-related measurement issues. REMS has been validated in adults and shows promise in pediatrics, despite the lack of reference values. The study is a single-center, national, non-profit interventional study lasting about 12 months. Participants will undergo REMS BMD measurement, clinical history collection, and assessment of anthropometric and pubertal parameters, with prior DXA data collected when available. The primary aim is to describe BMD values measured by REMS in pediatric osteoporosis, with secondary aims including subgroup analyses and comparison with DXA. A sample of 100 patients is planned. Statistical analyses will assess BMD distributions, correlations with clinical variables, and agreement between REMS and DXA using correlation coefficients and Bland-Altman analysis.

Inclusion Criteria:

• Written informed consent from adult patients or parents/legal guardians
• Age between 5 and 18 years
• Both sexes and all ethnicities
• Known condition negatively affecting bone health

Exclusion Criteria:

- Age below 5 years or over 18 years