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Osteogenisis Imperfecta (OI)-

 

            
            
             Osteogenisis imperfecta (OI) is "a rare genetic .
             disorder of collagen synthesis associated with broad .
             spectrum of musculoskeletal problems, most notably bowing .
             and fractures of the extremities, muscle weakness, .
             ligamentous laxity, and spinal deformities.".
             (Binder, 386). Other collagen-containing extraskeletal .
             tissues, such as the sclerae, the teeth, and the heart .
             valves are also affected to a variable degree. OI has a .
             "common feature of bony fragility associated with defective .
             formation of collagen by osteoblasts and fibroblasts." .
             (Smith, 1983, 13) This disease, involving defective .
             development of the connective tissues, is usually the result .
             of the autosomal dominant gene, but can also be the result .
             of the autosomal recessive gene. Spontaneous mutations are .
             common and the clinical presentation of the disease remains .
             to be quite broad. (Binder, 386) .
             OI is most commonly referred to as "brittle bones", .
             but other names include: fragilitas ossium, hypolasia of .
             the mesenchyme, and osteopsathyrosis. Osteogenisis .
             imperfecta is still not completely understood, and while .
             there have been advances in diagnosing the disease, .
             treatment is still limited.
             CAUSES.
             Osteogenisis imperfecta is the result of mutations .
             in the genes for type I collagen.
             In the mild dominantly inherited form of OI (type I), " a .
             non-functional allele for the alpha 1 (I) chain halves .
             collagen synthesis," (Smith, 1995, 169) and is largely .
             responsible for the inheritance. Single base mutations in .
             the codon for glycine causes lethal (type II) OI by wrecking .
             the formation of the collagen triple helix. Types III and .
             IV are the "less dram- atic outcomes of similar glycine .
             mutations in either the alpha 1 (I) or the alpha 2(I) .
             chains.(Smith, 1995, 169).
             The clinical signs can be caused from defective .
             osteoblastic activity and defective mesenchymal collagen .
             (embryonic connective tissue) and its derivatives, such as .
             sclera, bones, and ligaments.


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