title: Autosomal dominant osteopetrosis revisited: lessons from recent studies.
abstract: Systematic studies of autosomal dominant osteopetrosis (ADO) were followed by the identification of underlying mutations giving unique possibilities to perform translational studies. What was previously designated ADO1 turned out to be a high bone mass phenotype caused by a missense mutation in the first propeller of LRP5, a region of importance for binding inhibitory proteins. Thereby, ADO1 cannot be regarded as a classical form of osteopetrosis but must now be considered a disease of LRP5 activation. ADO (Albers-Schönberg disease, or previously ADO2) is characterized by increased number of osteoclasts and a defect in the chloride transport system (ClC-7) of importance for acidification of the resorption lacuna (a form of Chloride Channel 7 Deficiency Osteopetrosis). Ex vivo studies of osteoclasts from ADO have shown that cells do form normally but have reduced resorption capacity and an expanded life span. Bone formation seems normal despite decreased osteoclast function. Uncoupling of formation from resorption makes ADO of interest for new strategies for treatment of osteoporosis. Recent studies have integrated bone metabolism in whole-body energy homeostasis. Patients with ADO may have decreased insulin levels indicating importance beyond bone metabolism. There seems to be a paradigm shift in the treatment of osteoporosis. Targeting ClC-7 might introduce a new principle of dual action. Drugs affecting ClC-7 could be antiresorptive, still allowing ongoing bone formation. Inversely, drugs affecting the inhibitory site of LRP5 might stimulate bone formation and inhibit resorption. Thereby, these studies have highlighted several intriguing treatment possibilities, employing novel modes of action, which could provide benefits to the treatment of osteoporosis.
authors.affiliation: Section of Specialized Endocrinology, Medical Clinic B, Rikshospitalet, Oslo University Hospital, N-0027 Oslo, Norway. jens.bollerslev@medisin.uio.no
authors.forename: Jens
authors.initials: J
authors.lastname: Bollerslev
authors.forename: Kim
authors.initials: K
authors.lastname: Henriksen
authors.forename: Morten Frost
authors.initials: MF
authors.lastname: Nielsen
authors.forename: Kim
authors.initials: K
authors.lastname: Brixen
authors.forename: Wim
authors.initials: W
authors.lastname: Van Hul
mesh_terms: D001862:Bone Resorption / Q000235:genetics* / Q000473:pathology; D018118:Chloride Channels / Q000235:genetics*; D002986:Clinical Trials as Topic; D056726:Genetic Association Studies; D006801:Humans; D060492:Low Density Lipoprotein Receptor-Related Protein-5 / Q000235:genetics*; D010010:Osteoclasts / Q000473:pathology*; D010022:Osteopetrosis / Q000235:genetics* / Q000473:pathology
chemical_list: C097540:CLCN7 protein, human; D018118:Chloride Channels; C555482:LRP5 protein, human; D060492:Low Density Lipoprotein Receptor-Related Protein-5