Interestingly, patients suffering from a non-classical form of osteopetrosis, the autosomal dominant osteopetrosis type I (ADOI), which is caused by a specific gain-of-function mutation in the LRP5 gene and is associated with a high bone mass phenotype, have abnormally low number of osteoclasts in vivo[39]. Here, LRP5 is linked to osteopetrosis.