Osteoporosis in children with Prader-Willi syndrome

Osteoporosis is a skeletal disorder characterized by compromised bone strength and increased risk of fracture. Its severity is dependent on both bone mineral content and bone quality. Bone mineral, which accounts for about two-thirds of total bone strength, is commonly used to define osteoporosis. In the general population, bone mineral density, or amount of bone mineral per unit of bone mass, is relatively low in early life and gradually increases throughout childhood and adolescence, peaking during the third decade of life. Thereafter, progressive bone mineral loss occurs. Bone mineral density during childhood and adolescence is dependent on several factors including hormones (growth hormone, gonadal steroids, vitamin D), nutrition (particularly calcium), and neuromuscular stimulation (exercise). Deficiencies in any of these areas can lead to inadequate bone density and osteoporosis.

Significantly decreased total bone and spine mineral density and total bone mineral content are reported in PWS subjects but with no significant evidence of bone loss compared with controls suggesting a possible lack of bone mineral deposition during growth (e.g., adolescence). These changes may be due to low calcium and vitamin D intake with calorie-restricted diets and in the latter case, lack of sun exposure. Calcium and vitamin D supplements may be required. A program of physical activity may help prevent the development of osteoporosis by providing neuromuscular stimulation necessary for bone mineral deposition.

Decreased production of sex or growth hormones in individuals with PWS may also play a role. Growth hormone therapy, which is recommended for use in children with PWS, is associated with more normal bone mineral density. Gonadal steroid therapy may also help prevent osteoporosis. [Lee: 2000] [Allen: 2004]