**Question:** Which one of the following is not a feature of Phenylketonuria?

A. Hyperphenylalaninemia
B. Ketosis
C. Seizures
D. Macrocephaly

**Core Concept:**
Phenylketonuria (PKU) is an inherited disorder of amino acid التمثيل الغذائي, particularly phenylalanine, due to deficiency of phenylalanine hydroxylase (PAH) enzyme. PAH catalyzes the conversion of phenylalanine to tyrosine in the liver. When PAH is absent or dysfunctional, phenylalanine accumulates in the blood and brain, leading to neurological impairment and intellectual disability if not diagnosed and treated promptly.

**Why the Correct Answer is Right:**
D - Macrocephaly (enlarged head circumference) is a common feature of untreated PKU. However, treated PKU patients usually have normal head circumference.

**Why Each Wrong Option is Incorrect:**
A - Hyperphenylalaninemia is a correct feature of PKU, as the disorder results in elevated phenylalanine levels in the blood (hyperphenylalaninemia).
B - Ketosis is not a feature of PKU, as the disorder primarily affects phenylalanine levels and not ketone production.
C - Seizures can be a feature of untreated PKU, especially in the neonatal period. However, the correct answer should be "Macrocephaly" as it is not present in treated patients.

**Why the Correct Answer is Right:**
Macrocephaly is not a feature of treated PKU patients, as their elevated phenylalanine levels are controlled by a strict phenylalanine-restricted diet and/or pharmacotherapy. Macrocephaly is more likely to occur in untreated PKU patients whose raised phenylalanine levels cause brain damage, leading to developmental delay, seizures, and intellectual disability.

**Clinical Pearl:**
Early diagnosis and treatment of PKU is essential to prevent neurological complications. Parents of newborns should be advised to test their infants for PKU if they have a family history of PKU or live in an area with high PKU prevalence. Treatment includes a low-phenylalanine diet and/or pharmacotherapy with hydroxocobalamin (vitamin B12) and phenylalanine hydroxylase (PAH) enzyme replacement.

**Why Each Wrong Option is Incorrect:**
Option A (hyperphenylalaninemia) and Option C (seizures) are relevant features of untreated PKU. Option B (ketosis) is incorrect because PKU primarily affects phenylalanine levels, not ketone production. Option D (normal head circumference) is incorrect because untreated PKU patients may have macrocephaly due to brain damage caused by elevated phenylalanine levels, while treated patients have normal head circumference.