The remarkable finding that loss-of-function mutations in the Wnt coreceptor low-density lipoprotein receptor related protein 5 (LRP5) gene cause the osteoporosis-pseudoglioma syndrome (OPPG), a rare autosomal recessive disorder of severe juvenile osteoporosis and congenital blindness, and that gain-of-function mutations in this gene result in a high bone mass phenotype, provided first evidence for the considerable influence of Lrp5 signaling on bone remodeling [2], [3]. This evidence concerns the gene LRP5 and congenital stationary night blindness.