Which autosomal recessive condition causes accumulation of phenylalanine leading to intellectual disability if untreated?

Which autosomal recessive condition causes accumulation of phenylalanine leading to intellectual disability if untreated?

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

Answer: (B)

This question tests understanding of a metabolic disorder caused by an autosomal recessive enzyme defect that leads to buildup of a specific amino acid and brain damage if not treated. Phenylketonuria results from a deficiency of phenylalanine hydroxylase, so phenylalanine cannot be converted to tyrosine. The amino acid then accumulates in the blood and brain, causing intellectual disability and other neurodevelopmental issues if the condition isn’t managed early. Newborn screening detects elevated phenylalanine levels, allowing early dietary treatment that restricts phenylalanine and provides tyrosine as an essential amino acid. Avoiding phenylalanine-containing foods (and sometimes aspartame, which contains phenylalanine) helps prevent damage. Tay-Sachs involves a different substrate accumulation and presents with neurodegeneration due to GM2 buildup; red-green color blindness is not autosomal and isn’t about phenylalanine metabolism; lactose tolerance isn’t a metabolic disorder causing intellectual disability.

This question tests understanding of a metabolic disorder caused by an autosomal recessive enzyme defect that leads to buildup of a specific amino acid and brain damage if not treated. Phenylketonuria results from a deficiency of phenylalanine hydroxylase, so phenylalanine cannot be converted to tyrosine. The amino acid then accumulates in the blood and brain, causing intellectual disability and other neurodevelopmental issues if the condition isn’t managed early. Newborn screening detects elevated phenylalanine levels, allowing early dietary treatment that restricts phenylalanine and provides tyrosine as an essential amino acid. Avoiding phenylalanine-containing foods (and sometimes aspartame, which contains phenylalanine) helps prevent damage. Tay-Sachs involves a different substrate accumulation and presents with neurodegeneration due to GM2 buildup; red-green color blindness is not autosomal and isn’t about phenylalanine metabolism; lactose tolerance isn’t a metabolic disorder causing intellectual disability.