Discussion Author: clark brixey
Osteogenesis imperfecta (OI) is an inherited disorder of connective tissue (specifically, faulty collagen formation). Gene probes have elucidated mutations in genes that regulate collagen formation, resulting in defective conversion of reticulum fibers to adult collagen fibers. There are four clinical criteria â€” blue sclerae, fragile bones, otosclerosis, and poor dentition â€” the presence of two confirms the diagnosis.
There are four types of OI recognized:
Type I: Clinically, OI type I presents in late teenage years with blue sclerae and occasional deafness (otosclerosis); it is autosomal dominant-inherited with variable penetrance. This, the previously described â€śtardaâ€ť form, is characterized by thin, brittle bones that fracture repeatedly. These heal with exuberant callus formation, resultant skeletal bowing, and epiphyseal enlargement (overtubulation). In this progressive affliction beginning in infancy or early childhood, the rate of limb fractures decreases by the early teenage years. Other clinical hallmarks are a small triangular face and bulging skull. Deafness caused by otosclerosis may develop, but this is uncommon. Radiographically, a progressive kyphoscoliosis (40%) is noted, wormian bones are present, and multiple (healing) fractures are noted in gracile, osteopenic bones. Medullary rods may be needed to splint these bones.
Type II: OI type II is the lethal, previously described â€ścongenitalâ€ť, form that can be recognized on prenatal sonography by multiple fractures, demineralized calvaria, and a femur length more than 3 standard deviations below the mean for gestational age. Most of these infants are born prematurely, and many are stillborn; in addition, blue sclerae are always present. Type II is Autosomal Recessive-inherited.
Type III: OI type III features normal sclerae and progressive deformity of the limbs, with two thirds of infants presenting at birth with fractures having a great deal of callus formation.
Type IV: OI type IV is characterized by normal sclerae and variable skeletal involvement consisting of osteoporosis and occasional fractures, and the presence of discolored teeth.
OI has an equal gender incidence and no race predilection. Intramedullary rods correct bowing deformities and strengthen the bone to avoid new fractures.
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