LRP5 and osteoporosis: Mutations within the gene are known to lead to various bone disorders: gain-of-function mutations in the LRP5 gene can cause high-bone-mass (HBM) phenotypes in humans [7,8], whereas homozygous loss-of-function mutations cause osteoporosis-pseudoglioma syndrome (OPPG) characterized by early-onset osteoporosis and complications in eye development [9-11].