A 6-month-old infant has been exclusively fed a commercially available infant formula. Upon introduction of fruit juices, however, the child develops jaundice, hepatomegaly, vomiting, lethargy, irritability, and seizures. Tests for urine-reducing substances are positive. Which of the following is likely to explain this child's condition?
a) Galactokinase deficiency
b) Fructose-1,6-bisphosphatase deficiency
c) Hereditary fructose intolerance
d) Lactose intolerance