What metabolic consequence occurs in PKU due to PAH deficiency?

• A. Phenylalanine Accumulates; Tyrosine Becomes Deficient
• B. Tyrosine Accumulates; Phenylalanine Becomes Deficient
• C. Both Phenylalanine and Tyrosine Accumulate
• D. No Change in Phenylalanine Or Tyrosine Levels

Answer: (A)

When phenylalanine hydroxylase is deficient, the pathway that turns phenylalanine into tyrosine can’t proceed. This causes phenylalanine to build up in the body while tyrosine production drops, making tyrosine scarce and often requiring it to be obtained from the diet. That’s why the correct description is that phenylalanine accumulates and tyrosine becomes deficient. The other scenarios don’t fit the defect: tyrosine wouldn’t accumulate, there would be a change from normal levels, and both amino acids wouldn’t rise simultaneously.