Osteogenesis imperfecta
Genetic defect of Type I collagen. Autosomal dominant but there are sporadic cases.
Types
Type I
Collagen is normal but insufficient quantities. Most mild form. Bones fracture easily, slight spinal curvature, loose joints, poor muscle tone, blue-gray sclera, early hearing loss, slight protrusion of the eyes.
Type II
Collagen is not of a sufficient quality or quantity. Most cases die within the first year of life due to respiratory failure or intracerebral hemorrhage.
Type III
Type III is distinguished among the other classifications as being the "Progressive Deforming" type, wherein a neonate presents with mild symptoms at birth and develops the aforementioned symptoms throughout life. Lifespan may be normal, albeit with severe physical handicapping. Collagen quantity is sufficient but is not of a high enough quality.
Type IV
Collagen quantity is sufficient but is not of a high enough quality. Bones fracture easily, especially before puberty. Short stature, spinal curvature and barrel-shaped rib cage, bone deformity is mild to moderate, discolouration of the sclera and early loss of hearing.
Type V
Same clinical features as Type IV. Distinguished histologically by "mesh-like" bone appearance. Further characterized by the "V Triad" consisting of a) radio-opaque band adjacent to growth plates, b) hypertrophic calluses at fracture sites, and c) calcification of the radio-ulnar interosseous membrane.
Type VI
Same clinical features as Type IV. Distinguished histologically by "fish-scale" bone appearance.
