This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
A child has tnicrocephaly, blue eyes, Fair skin, and Mental retardation, Ferric chloride test is positive.What is the likely diagnosis - 
Select and explain. 
A. Phenylketonuria (PKU), B. Homocystinuria, C. Tyrosinosis, D. Alkaptonuria
A: Phenylketonuria (PKU)
Answer: A: Phenylketonuria (PKU) 
Explanation: Clinical manifestations of phenylketonuria 

Normal at birth
Symptoms occur after 1 months -


Mental retardation → Not present at birth, develops gradually.
Neurological signs Irritability, tremors, convulsions, hyperkinesis and muscular hypertonia & exaggerated reflex.
Blond hair, blue iris, fair skin.
Musty or mousy body odor.
Vomiting
Microcephaly
Enamel hypoplasia & Growth retardation