Which autosomal recessive condition is managed by restricting dietary phenylalanine to prevent intellectual disability?

• A. Tay-Sachs disease
• B. Phenylketonuria (PKU)
• C. Red-green color blindness
• D. Achondroplasia

Answer: (B)

Phenylketonuria (PKU) is an autosomal recessive metabolic disorder in which the enzyme that converts phenylalanine to tyrosine is deficient. Because phenylalanine then builds up in the body, especially affecting the developing brain, restricting phenylalanine in the diet prevents intellectual disability and supports normal cognitive development when started early. Tyrosine becomes essential and is often added to the diet as the body can’t make enough of it from phenylalanine anymore. Newborn screening helps catch PKU so treatment can begin promptly, and lifelong dietary management is usually needed to maintain normal development. Other options don’t fit because Tay-Sachs involves a different enzyme defect with no diet that prevents neurodegeneration; red-green color blindness is usually X-linked and not managed by phenylalanine restriction; achondroplasia is autosomal dominant and unrelated to this dietary approach.