A 2-Year-Old Caucasian Boy Is Brought to the Pediatric Clinic

A 2-year-old Caucasian boy is brought to the pediatric clinic for failure to gain weight. The child's mother states that he has frequent foul-smelling stools, with a greasy appearance, and has had three hospitalizations for pneumonia. Which of the following defects is responsible for this child's symptoms?

A) Lack of phenylalanine hydroxylase
B) Deficiency of galactokinase
C) Defective epithelial chloride transport
D) Amino acid substitution on the hemoglobin beta chain
E) Defect in hypoxanthine-guanine phosphoribosyltransferase