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: Biochemistry
An infant presents to OPD with a history of vomiting and poor feeding. Musty odor is present in baby's urine. Guthrie test was done and found to be positive. The most likely diagnosis is? 
Select and explain. 
A. Phenylketonuria, B. Alkaptonuria, C. Tyrosinemia, D. Maple syrup urine disease
A: Phenylketonuria
Answer: A: Phenylketonuria 
Explanation: Clinical Presentation of Phenylketonuria 

The affected infant is normal at birth. 
Profound intellectual disability develops gradually if the infant remains untreated. 
Vomiting, sometimes severe enough to be misdiagnosed as pyloric stenosis. 
Older untreated children become hyperactive with autistic behaviors including purposeless hand movements, rhythmic rocking and athetosis. 
The infants are lighter in their complexion than unaffected (Phenylalanine not converted to Tyrosine, so decreased melanin synthesis).
These children have an unpleasant mousy or musty odor of phenylacetic acid.

Lab Diagnosis of PKU
Guthrie Test (Bacterial Inhibition Assay of Guthrie).

Rapid screening test in the blood sample.
First method used for this purpose.

Reference- Harper’s illustrated biochemistry. 30th edition page -304