A term born 6-month-old, lethargic blonde infant, presented with multiple episodes of vomiting, poor feeding, convulsions and severe psychomotor retardation. O/E: – Microcephaly with prominent maxillae and widely spaced teeth Blue iris Seborrheic or eczematoid rash Spasticity, hyperreflexia, and tremor Musty odour of urine MRI brain All of the following statements are true about the disease except: –

**Core Concept**
The infant's symptoms, including microcephaly, seizures, and psychomotor retardation, are suggestive of a congenital metabolic disorder. This condition affects the body's ability to metabolize certain compounds, leading to a buildup of toxic substances.

**Why the Correct Answer is Right**
The infant's presentation is consistent with Phenylketonuria (PKU), a genetic disorder caused by a deficiency of the enzyme phenylalanine hydroxylase. This enzyme is essential for the breakdown of phenylalanine, an amino acid found in many protein-rich foods. In PKU, phenylalanine accumulates and is converted to phenylpyruvic acid, which is toxic to the brain. The musty odor of the urine is a classic sign of PKU due to the presence of phenylacetate and phenylpyruvate.

**Why Each Wrong Option is Incorrect**
**Option A:** PKU is an autosomal recessive disorder, not X-linked.
**Option B:** The disease is characterized by intellectual disability, not just psychomotor retardation.
**Option C:** The infant's MRI brain would likely show white matter abnormalities, not just a normal brain structure.

**Clinical Pearl / High-Yield Fact**
PKU is a treatable condition if diagnosed early. A newborn screening test can detect high levels of phenylalanine in the blood, allowing for prompt initiation of dietary restrictions and supplements to prevent brain damage.

**Correct Answer:** D.

✓ Correct Answer: C. The complications can't be prevented by restricting the use of the involved amino acid in diet.