Ans. (d). through diet.
PKU (phenylktonuria) is a genetic disorder, characterized by decreased metabolism of phenylalanine amino acid. It is caused by mutation in the gene that codes for phenylalanine hydroxylase, enzyme responsible for phenylalanine metabolism.
If untreated, PKU leads to mental problems, seizures or intellectual disabilities. The one way to treat intellectual disabilities can be done by regulated diet.
Patients are advised to take strict diet, with limited or minimum amount of phenylalanine, such as red meat, milk, and eggs.
Thus, the correct answer is option (d).