MedGen

A constitution or condition of the body which makes the tissues react in special ways to certain extrinsic stimuli and thus tends to make the individual more than usually susceptible to certain diseases. [from MONDO]

Juvenile primary osteoporosis is a skeletal disorder characterized by thinning of the bones (osteoporosis) that begins in childhood. Osteoporosis is caused by a shortage of calcium and other minerals in bones (decreased bone mineral density), which makes the bones brittle and prone to fracture. Affected individuals often have multiple fractures in the long bones of the arms and legs, especially in the regions where new bone forms (metaphyses). They also have fractures in the bones that form the spine (vertebrae), which can cause collapse of the affected vertebrae (compressed vertebrae). Multiple fractures can cause bone pain and lead to movement problems. [from MedlinePlus Genetics]