A 2-Year-Old Boy Is Evaluated for Easy Bruising

A 2-year-old boy is evaluated for easy bruising.  His parents report that he develops marked bruising and open wounds following minor trauma.  The skin is difficult to suture due to its extreme fragility.  Physical examination reveals hyperextensible skin, multiple ecchymoses over the forearms and pretibial regions, and an umbilical hernia.  A skin biopsy is performed, and histochemical evaluation of the biopsy reveals a defect in extracellular processing of collagen.  Which of the following steps of collagen synthesis is most likely impaired in this patient?

A) Glycosylation of hydroxylysine residues
B) Interchain C-terminal disulfide bond formation
C) N-terminal propeptide removal
D) Proline residue hydroxylation
E) Triple helix formation