03-11-2008, 11:48 AM
40.
A newborn female has a large and distorted cranium, short and deformed limbs, and very blue scleras (whites of the eyes). Radiographs demonstrate multiple limb fractures and suggest a diagnosis of osteogenesis imperfecta (brittle bone disease). Analysis of type I collagen protein, a triple helix formed from two 1 and one 2 collagen chains, shows a 50% reduction in the amount of type I collagen in the baby's skin. DNA analysis demonstrates the presence of two normal 1 alleles and one normal 2 allele. Which of the following is the best explanation of these results?
A. Deficiency of 1 collagen peptide synthesis
B. Inability of 1 chains to incorporate into triple helix
C. Defective 1 chains that interrupt triple helix formation
D. Incorporation of defective 2 chains that cause instability and degradation of the triple helix
E. A missense mutation that alters the synthesis of 1 chains
A newborn female has a large and distorted cranium, short and deformed limbs, and very blue scleras (whites of the eyes). Radiographs demonstrate multiple limb fractures and suggest a diagnosis of osteogenesis imperfecta (brittle bone disease). Analysis of type I collagen protein, a triple helix formed from two 1 and one 2 collagen chains, shows a 50% reduction in the amount of type I collagen in the baby's skin. DNA analysis demonstrates the presence of two normal 1 alleles and one normal 2 allele. Which of the following is the best explanation of these results?
A. Deficiency of 1 collagen peptide synthesis
B. Inability of 1 chains to incorporate into triple helix
C. Defective 1 chains that interrupt triple helix formation
D. Incorporation of defective 2 chains that cause instability and degradation of the triple helix
E. A missense mutation that alters the synthesis of 1 chains