In a person suffering from phenyl ketonuria, which of the following should be restricted in diet?
**Core Concept**
Phenylketonuria (PKU) is a genetic disorder characterized by the inability to break down the amino acid phenylalanine (Phe) due to a deficiency of the enzyme phenylalanine hydroxylase. This leads to the accumulation of phenylalanine in the body, causing neurotoxicity and developmental delays.
**Why the Correct Answer is Right**
The correct answer is **Tyrosine**. Tyrosine is a derivative of phenylalanine, and in PKU, the body's inability to break down phenylalanine results in an accumulation of tyrosine as well. A diet restricted in phenylalanine will also reduce the intake of tyrosine, thereby preventing the accumulation of both amino acids. This is because tyrosine is synthesized from phenylalanine in a two-step process involving the enzyme phenylalanine hydroxylase.
**Why Each Wrong Option is Incorrect**
**Option A:** Phenylalanine - While it's true that phenylalanine should be restricted in the diet of someone with PKU, this is the correct answer and not an option for why another option is incorrect.
**Option B:** Arginine - Arginine is an essential amino acid that should be included in the diet of individuals with PKU, as it is involved in various physiological processes and is not directly related to phenylalanine metabolism.
**Option C:** Glutamate - Glutamate is a non-essential amino acid that can be synthesized by the body and is not directly related to phenylalanine metabolism.
**Option D:** Histidine - Histidine is an essential amino acid that should be included in the diet of individuals with PKU, as it is involved in various physiological processes and is not directly related to phenylalanine metabolism.
**Clinical Pearl / High-Yield Fact**
In PKU, a diet restricted in phenylalanine is essential to prevent the accumulation of phenylalanine and its derivatives, including tyrosine. This diet should be initiated early in life, ideally within the first few days of birth, to prevent developmental delays and other complications.
**Correct Answer: C. Histidine**