On the pathogenesis of osteogenesis imperfecta: some insights of the Utah paradigm of skeletal physiology.
The pathogenesis of osteogenesis imperfecta (OI) baffled physiologists and physicians for over a century. Most past efforts to explain it depended heavily on cell and molecular biology and on changes in the material properties of affected bones (an old idea that OI patients could not make enough bone erred). To such views the still-evolving Utah paradigm of skeletal physiology can add a model for bone and bones that depends on errors in three genetically-determined features. The errors include, 1,2) elevated 'set points' of the strain-dependent thresholds that help to control how lamellar bone modeling and remodeling adapt bone strength, architecture and 'mass' to the voluntary loads on load-bearing bones; 3) and a reduced modeling-rate limit for the appositional rate of the lamellar bone formation drifts that can increase bone strength, outside bone diameters, cortical and trabecular thickness, and bone 'mass'. If only abnormalities #1,#2 occurred, that should limit the eventual strength, architecture and 'mass' of load-bearing bones, while if only #3 occurred that should prolong or delay how long it took to achieve the above limits, but without changing them. Equally, in driving from New York to Boston, stopping at New Haven would prevent reaching Boston no matter how rapidly one drove (a limited trip). But by not stopping one could reach Boston by driving very slowly (a prolonged but not a limited trip). This model concerns general features of bone and bones in OI that would need study and explanation at the tissue, cellular and molecular-biologic levels. Other places and people must discuss any devils in the details, as well as collagenous tissue, auditory, dental and other problems in OI, and the effects of treatment on the above features.
Frost
H M
HM
Department of Orthopaedic Surgery, Southern Colorado Clinic, Pueblo, CO 81008-9000, USA.