The prevalence of juvenile primary osteoporosis is unknown. Nearly 1 in 10 adults over age 50 have osteoporosis, but the condition is uncommon in children. Osteoporosis can occur at a young age as a feature of other conditions but rarely occurs without other signs and symptoms (primary osteoporosis).

Mutations in the LRP5 gene can cause juvenile primary osteoporosis. This gene provides instructions for making a protein that participates in a chemical signaling pathway that affects the way cells and tissues develop. In particular, the LRP5 protein is involved in the regulation of bone mineral density.

LRP5 gene mutations that cause juvenile primary osteoporosis result in an LRP5 protein that cannot transmit signals along the pathway. The resulting reduction in signaling impairs proper bone development, causing decreased bone mineral density and osteoporosis at a young age.

Many people with childhood-onset osteoporosis do not have a mutation in the LRP5 gene. (When its cause is unknown, the condition is often called idiopathic juvenile osteoporosis). It is likely that mutations in other genes that have not been identified are involved in this condition.