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Recurrent limb and vertebral fractures are typical for patients with osteogenesis imperfecta (OI). Primary Osteoporosis Affecting Collagen (Osteogenesis Imperfecta) 2.1.1. In fact, they continue holding secrets which may open doors for drug developments in rare and common osteoporosis. Medical research has unveiled many monogenic bone fragility conditions, yet their mechanisms of disease remain incompletely understood. Traditionally, bone fragility is understood as resulting from reduced bone mass, or from defects in bone matrix composition or mineralization. Bone fragility can originate from alterations in all these components, be it the genetic blueprint, mechanical loading, insufficient remodeling at old age, estrogen deficiency or chronic medical conditions affecting bone accrual, structure or composition. The extracellular matrix of bone tissue is composed of inorganic minerals, collagen, water, non-collagenous proteins and lipids. Bone tissue contains three distinct cell types: (i) the osteoblasts, derived from mesenchymal cells, which deposit new bone tissue (ii) osteoclasts, derived from bone marrow hematopoietic precursor cells, which break down bone matrix and (iii) osteocytes (former osteoblasts) which orchestrate the activity of osteoblasts and osteoclasts as a response to mechanical strain.
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Developing bones consist of cartilaginous joints, the epiphysis, the growth plate cartilage with adjacent osteogenesis and the cortical and cancellous bone mineralized structure.