A normal born child presents with mental retardation, blond hair and convulsions at 1 year of age. Most probable diagnosis is?
**Core Concept**
The child's symptoms suggest a genetic disorder affecting brain development, hair pigmentation, and seizure susceptibility. This condition is caused by a mutation in a gene responsible for the production of an enzyme involved in the metabolism of a crucial amino acid.
**Why the Correct Answer is Right**
The symptoms described are characteristic of Phenylketonuria (PKU), a genetic disorder caused by a deficiency of the enzyme phenylalanine hydroxylase (PAH). PAH is essential for converting phenylalanine (Phe) to tyrosine, an amino acid necessary for brain development and neurotransmitter synthesis. In PKU, Phe accumulates in the blood and brain, leading to intellectual disability, blond hair, and increased seizure risk. The condition is inherited in an autosomal recessive pattern.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not a recognized genetic disorder causing mental retardation, blond hair, and convulsions.
**Option B:** This option is not related to the symptoms described in the question.
**Option C:** This option is not a genetic disorder affecting brain development and hair pigmentation.
**Clinical Pearl / High-Yield Fact**
PKU is a classic example of a genetic disorder with a well-known environmental trigger: a diet high in phenylalanine-containing foods. Early diagnosis and treatment, including dietary restrictions, can significantly improve outcomes in affected individuals.
**Correct Answer: C. Phenylketonuria (PKU)**