A child with a large head, multiple fractures, and blue sclerae (whites of the eyes) is evaluated for osteogenesis imperfecta. O
ne study involves labeling of collagen chains in tissue culture to assess their mobility by gel electrophoresis. Amino acids labeled with radioactive carbon 14 are added to the culture dishes in order to label the collagen. Which of the following amino acids would not result in labeled collagen? a. Serine
b. Glycine
c. Aspartate
d. Glutamate
e. Hydroxyproline
Explanation: Osteogenesis imperfecta is a systemic heritable disorder of connective tissue whose cardinal manifestation is bone fragility - i.e. it is characterized by brittle bones that easily fracture. Hydroxyproline employed in radioactive labeling would not result in labeled collagen because it is not incorporated per se during the synthesis of collagen.
