What genetic disorder is characterized by the inability to metabolize phenylalanine?

• A. Down syndrome
• B. Galactosemia
• C. PKU
• D. Marfan syndrome

Answer: (C)

The genetic disorder characterized by the inability to metabolize phenylalanine is phenylketonuria (PKU). PKU is caused by a mutation in the gene that encodes the enzyme phenylalanine hydroxylase, which is responsible for converting phenylalanine into tyrosine. When this enzyme does not function properly, phenylalanine accumulates in the body, leading to various neurological issues and intellectual disabilities if not managed through dietary restrictions.

Early diagnosis through newborn screening and strict adherence to a diet low in phenylalanine can prevent the adverse effects associated with PKU. This disorder is a classic example of how metabolic disorders can have significant developmental implications if not addressed early on.

Other genetic disorders listed do not involve the metabolism of phenylalanine. Down syndrome is a chromosomal condition associated with the presence of an extra chromosome 21. Galactosemia involves the inability to metabolize galactose, and Marfan syndrome affects connective tissue, leading to a variety of physical manifestations but is unrelated to phenylalanine metabolism. Hence, PKU is the only correct choice in this context.