Answer:USMLE step 2 Mcq 93:An 11 year old girl is noted to be rather short. She has a history of frequent bone fractures following minor trauma

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Correct Answer: A
Explanation:
Accurate diagnosis of osteogenesis imperfecta is especially critical because of the not uncommon dilemma of distinguishing whether recurrent fractures in a young child represent brittle bones or child abuse. Type I osteogenesis imperfecta is the most common form and is associated with wide intrafamilial variability. One patient might be extremely short of stature, with frequent fractures and considerable disability, whereas an affected relative leads an unencumbered, vigorous life. Type II encompasses the class of 'osteogenesis imperfecta congenita' variants, most of which are lethal in infancy, if not in utero. Type III osteogenesis imperfecta comprises miscellaneous phenotypes that cannot be classified better. Most cases include severe skeletal deformity and short stature as distinguishing features. Most occur sporadically.Type IV osteogenesis imperfecta is similar to type I, only rarer and not associated with blue sclerae. Some patients with types I or IV have few fractures or may escape them entirely, although blue sclerae, short stature or deafness indicates the presence of the mutant gene. Brittleness and deformability result from a defect in the collagenous matrix of bone. The skeletal aspect of osteogenesis imperfecta is, therefore, a hereditary form of osteoporosis. Scalloping of the superior and inferior vertebral bodies by pressure from the expansible intervertebral disc or flat vertebrae are observed, particularly in older patients in whom senile or postmenopausal changes exaggerate the change, or young patients immobilized after fracture or orthopedic surgery. Usually the frequency of fractures decreases at puberty for patients with types I, III, and IV. Loose-jointedness is sometimes striking in type I osteogenesis imperfecta; dislocation of joints can result from deformity secondary to repeated fracture, ligamentous laxity, or rupture of tendons (especially the Achilles and patellar). Blue or bluish-gray sclerae are present in types I, II, and III osteogenesis imperfecta and are a valuable clue to the diagnosis. The cornea, like the sclera, is abnormally thin. The ocular features are usually not of great functional importance. Hearing loss becomes detectable in many patients by the second or third decade of life. The characteristic dental manifestation of osteogenesis imperfecta is opalescent teeth caused by a defect in dentin morphogenesis .


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