Genetic determinants of bone mass.
OBJECTIVE
This review examines recent advances in the analysis of genetic determinants of bone mass. It addresses both human and animal linkage studies as well as genetic manipulations in animals, inbred mouse models, and candidate gene analyses.


RESULTS
Recent studies have implicated novel regulatory pathways in bone biology including both the neuroendocrine system and metabolic pathways linked to lipid metabolism. Variations in the lipoprotein receptor-related protein 5 (LRP5), part of the Wnt-frizzled pathway, were independently identified by linkage in high and low bone mass families. Subsequently, other high bone mass syndromes have been shown to have mutations in this gene. Neural studies have shown the skeletal regulatory activity of leptin and neuropeptide Y receptors via the hypothalamus. Subsequently, the beta-adrenergic pathway has been implicated, with important changes in bone mass. The lipoxygenase 12/15 pathway, identified through inbred mouse models and through pharmacologic studies with specific inhibitors, has also been shown to have important effects on bone mass. These studies exemplify the value of genetic models both to identify and then confirm pathways by mutational study and pharmacologic interventions. Continuing candidate gene studies often performed with multiple loci complement such discoveries. However, these studies have not focused on the clinical endpoint of fracture and few have included large enough groups to engender confidence in the associations reported, as such studies may require thousands of individuals. Interestingly, results often differ by ethnicity, age, or gender. A small proportion have examined whether relevant genes influence response to treatment.


CONCLUSIONS
The combinations of human and animal genetic linkage studies have advanced understanding of the regulation of bone mass. Studies ranging from linkage to pharmacology provide optimism for new targets and treatments for osteoporosis.
Baldock
P A
PA
Bone and Mineral Research Program, Garvan Institute of Medical Research, St. Vincent's Campus and University of New South Wales, Sydney, Australia.
Eisman
John A
JA
D000818:Animals; D015519:Bone Density / Q000235:genetics*; D006801:Humans; D026502:LDL-Receptor Related Proteins; D020738:Leptin / Q000235:genetics; D060492:Low Density Lipoprotein Receptor-Related Protein-5; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation; D009478:Neuropeptide Y / Q000235:genetics; D011943:Receptors, Adrenergic, beta / Q000235:genetics; D011973:Receptors, LDL
D026502:LDL-Receptor Related Proteins; C555482:LRP5 protein, human; D020738:Leptin; D060492:Low Density Lipoprotein Receptor-Related Protein-5; C555483:Lrp5 protein, mouse; D009478:Neuropeptide Y; D011943:Receptors, Adrenergic, beta; D011973:Receptors, LDL