The importance of these transmembrane co-receptors in bone was revealed by the description of mutations in LRP5 that caused two diametrically opposed bone phenotypes: osteoporosis pseudoglioma syndrome (OPPG), and the high bone mass (HBM) phenotype [38,50,51] (Table 1 and Figure 2). The gene discussed is LRP5; the disease is Osteoporosis - pseudoglioma.