1. A 6-month-old boy is brought to the pediatrician by his parents, who are first cousins. This is their first child. Physical examination reveals a small, thin, lethargic infant with slightly misshapen long bones. His features are somewhat coarse. Joint movements are restricted, his corneas are clouded, and his gums are underdeveloped. His liver is not enlarged. Serum levels of acid hydrolases are found to be elevated. The child most likely has a defect in which of the following metabolic activities?