Radiographic studies of a 2 year old child brought to an emergency room reveal a new fracture of the humerus and evidence of multiple old fractures in ribs and long bones of the extremities. A social worker wants to initiate prosecution of the parents for child abuse, but an ale emergency room physician notices that, despite the broken arm, the toddler shows minimal bruising. A very careful, directed, physical examination reveals that the toddler has "peculiar teeth," a blue tinge to the sclera, and unusually mobile joints. The disease that the physician suspects the child has is characterized by an abnormality of which of the following biochemical functions?
The child has the most common variant (type I) of osteogenesis imperfecta, which is an autosomal dominant genetic defect in the synthesis of type I collagen, due to decreased synthesis of the procollagen alpha1(1) amino acid chain. This defect (unlike that of the perinatal, lethal, type II form of osteogenesis imperfecta) is compatible with survival, but does cause skeletal fragility, dentinogenesis imperfecta (abnormal teeth), blue sclera, joint laxity, and hearing impairment. Unfounately, a number of families with this defect have had their children removed because of "abuse," only to find that the broken bones continue in the new environment. Type I collagen is found in skin, bone, tendons, and most other organs. Type II collagen is found in cailage and vitreous humor. Type III collagen is found in blood vessels, uterus, and skin. Type IV collagen makes basement membranes. Ref: Barbul A., Efron D.T. (2010). Chapter 9. Wound Healing. In F.C. Brunicardi, D.K. Andersen, T.R. Billiar, D.L. Dunn, J.G. Hunter, J.B. Matthews, R.E. Pollock (Eds), Schwaz's Principles of Surgery, 9e.
Collagen type I synthesis
Collagen type II synthesis
Collagen type III synthesis
Collagen type IV synthesis