What genetic disorder is associated with the lack of an enzyme necessary for the normal metabolism of the amino acid phenylalanine?

a. marfan syndrome
b. phenylketonuria (pku)
c. huntington disease
d. sickle cell disease
e. cystic fibrosis (cf)

The correct answer is b. phenylketonuria (PKU)

Explanation:

Phenylketonuria (PKU) is a genetic disorder in which an amino acid called phenylalanine accumulates in the body. It occurs due to the mutation in a gene that codes for an enzyme called phenylalanine hydroxylase.  

This enzyme is necessary for breaking down the phenylalanine in the body. As in phenylketonuria (PKU), this enzyme becomes defective so dietary phenylalanine starts accumulating in the body which cause this disorder.  

Some symptoms of this disease are neurological problems, rashes on the skin, hyperactivity, behavioral disorders, etc. So the correct answer is b.