Although osteoporosis has been de? ned as a metabolic bone disease characterized by low bone mass and microarchitectural deterioration of bone tissue leading to enhanced bone fragility and a consequent increase in fracture risk, it is not clear that osteoporosis represents a single disease as much as a similar response of bone to different pathophysiologies. In the 1940s Fuller Albright and colleagues recognized osteoporosis of old age and distinguished it from osteoporosis associated with the postme- pausal state, as well as from osteoporosis from disuse, osteoporosis from malnutrition, and...