Bone is an extremely dynamic and adaptive tissue, whose metabolism and homeostasis is influenced by many different hormonal, mechanical, nutritional, immunological and pharmacological stimuli. Genetic factors significantly affect bone health, through their influence on bone cells function, cartilage quality, calcium and vitamin D homeostasis, sex hormone metabolism and pubertal timing. In addition, optimal nutrition and physical activity contribute to bone mass acquisition in the growing age. All these factors influence the attainment of peak bone mass, a critical determinant of bone health and fracture risk in adulthood. Secondary osteoporosis is an important issue of clinical care in children with acute and chronic diseases. Systemic autoimmune disorders, like juvenile idiopathic arthritis, can affect the skeletal system, causing reduced bone mineral density and high risk of fragility fractures during childhood. In these patients, multiple factors contribute to reduce bone strength, including systemic inflammation with elevated cytokines, reduced physical activity, malabsorption and nutritional deficiency, inadequate daily calcium and vitamin D intake, use of glucocorticoids, poor growth and pubertal delay. In juvenile arthritis, osteoporosis is more prominent at the femoral neck and radius compared to the lumbar spine. Nevertheless, vertebral fractures are an important, often asymptomatic manifestation, especially in glucocorticoid-treated patients. A standardized diagnostic approach to the musculoskeletal system, including prophylaxis, therapy and follow up, is therefore mandatory in at risk children. Here we discuss the molecular mechanisms involved in skeletal homeostasis and the influence of inflammation and chronic disease on bone metabolism.

Disorders of sexual development (DSDs) are characterized by a heterogeneous group of congenital conditions associated with atypical development of the sex chromosomes, gonadal or anatomical sex. We report the case of a child with an isolated micropenis, a typical feature of the 46,XY DSD showing low basal testosterone levels and post-stimulation with the hCG test. Molecular analysis using a next-generation sequencing (NGS) panel of 50 genes involved in DSDs was performed, revealing a heterozygous mutation, c.1040G > ANM_000102.4, in the CYP17A1 gene. Sanger sequencing was used to confirm the gene variant detected by NGS; it was also performed to his parents, revealing the presence of the same mutation in the mother, who presented no features of the disease. Then, the serum steroid profile was determined by liquid chromatography coupled to tandem mass spectrometry analysis. Interestingly, this analysis highlighted low levels of testosterone, progesterone, and dehydroepiandrostenedione, as also confirmed by a stimulus test with ACTH. These results suggest that, in some cases, heterozygous mutations in recessive genes involved in adrenal steroidogenesis can also affect the patient’s phenotype.