What deficiency causes phenylketonuria?

What deficiency causes phenylketonuria?

• A. Deficiency of the enzyme converting phenylalanine to tyrosine
• B. Deficiency of the enzyme converting tyrosine to phenylalanine
• C. Deficiency of the enzyme converting leucine to isoleucine
• D. Deficiency of the enzyme converting methionine to homocysteine

Answer: (A)

Phenylketonuria (PKU) results from a deficiency in the enzyme phenylalanine hydroxylase, which is responsible for converting phenylalanine to tyrosine. In individuals with PKU, the inability to effectively metabolize phenylalanine leads to its accumulation in the body, resulting in a variety of neurological and developmental issues if not managed through diet. As phenylalanine is an essential amino acid, its excessive levels can be toxic to the brain, leading to cognitive impairments and other health issues.

The other processes mentioned involve different amino acids and enzymes that do not relate to the metabolic pathway affected in phenylketonuria. Therefore, understanding that the linkage of phenylalanine to tyrosine metabolism is crucial to explaining the enzyme deficiency's role in PKU.