What is phenylketonuria (PKU) and how is it nutritionally managed?

• A. PKU is a deficiency of calcium; managed with high-phenylalanine diet.
• B. PKU is an inability to metabolize fat; managed with ketogenic diet.
• C. PKU is a liver disease causing cholesterol accumulation; managed with statins.
• D. PKU is an inability to metabolize phenylalanine; management requires lifelong low-phenylalanine diet with specialized formulas.

Answer: (D)

PKU is an inherited metabolic disorder caused by insufficient activity of the enzyme phenylalanine hydroxylase, so phenylalanine from dietary protein cannot be converted to tyrosine. This leads to elevated phenylalanine levels that can damage brain development if not controlled. Nutritional management centers on a lifelong, very low-phenylalanine diet guided by regular monitoring of blood phenylalanine levels. This typically involves using specialized medical formulas that provide essential amino acids and calories without phenylalanine, while restricting high-protein foods such as dairy, meat, fish, eggs, and most grains. Tyrosine becomes an essential amino acid in PKU and is often provided through these formulas. Early detection via newborn screening and ongoing diet adjustment are key to preventing intellectual and developmental problems. Other descriptions—calcium deficiency, fat metabolism issues requiring a ketogenic diet, or liver disease treated with statins—do not describe PKU.